Forums

Li-Ion questions (charger, fast-cycling)

Started by Joerg October 3, 2016
Hi Folks,

Just bought another Li-Ion deal with charger:

https://images-na.ssl-images-amazon.com/images/I/41HL6Xmx1qL._SX466_.jpg

The charger is like this little guy, a switcher that can deliver 1 amp:

https://images-na.ssl-images-amazon.com/images/I/41HL6Xmx1qL._SX466_.jpg

The typical battery is two cell bundles in series so 8.4V max. To my 
surprise the charger has 10.2V open loop voltage. It is not a switched 
deal to overcome wire resistance where it measures the battery voltage 
every once in a while. Just straight DC. It seems that it relies on the 
battery's "electric safety vent" to stop at 8.4V. Anybody seen this done?

It's not a problem to build a proper charger that limits at 8.4V or 
ideally 200mV less. Because of cable resistance it'll be sluggish 
towards the end but I can leave it connected all night. Just puzzled 
that they do this. It's the same 10.2V on the system I already have, I 
just never measured.

Other: I read several times that Li-Ion does not like fast charge 
discharge cycling like you have in a car. Yet one can buy Li-Ion car 
batteries now. Reason I ask is that I am thinking about reducing the 
size of a bicycle Li-Ion battery and using a dynamo to replenish. Given 
the hills around here that will be a see-saw deal where it goes from net 
charging to net discharging dozens of times per ride. Is that ok with 
Li-Ion?

-- 
Regards, Joerg

http://www.analogconsultants.com/
On Mon, 03 Oct 2016 16:27:12 -0700, Joerg wrote:

> Hi Folks, > > Just bought another Li-Ion deal with charger: > > https://images-na.ssl-images-amazon.com/images/I/41HL6Xmx1qL._SX466_.jpg > > The charger is like this little guy, a switcher that can deliver 1 amp: > > https://images-na.ssl-images-amazon.com/images/I/41HL6Xmx1qL._SX466_.jpg > > The typical battery is two cell bundles in series so 8.4V max. To my > surprise the charger has 10.2V open loop voltage. It is not a switched > deal to overcome wire resistance where it measures the battery voltage > every once in a while. Just straight DC. It seems that it relies on the > battery's "electric safety vent" to stop at 8.4V. Anybody seen this > done? > > It's not a problem to build a proper charger that limits at 8.4V or > ideally 200mV less. Because of cable resistance it'll be sluggish > towards the end but I can leave it connected all night. Just puzzled > that they do this. It's the same 10.2V on the system I already have, I > just never measured. > > Other: I read several times that Li-Ion does not like fast charge > discharge cycling like you have in a car. Yet one can buy Li-Ion car > batteries now. Reason I ask is that I am thinking about reducing the > size of a bicycle Li-Ion battery and using a dynamo to replenish. Given > the hills around here that will be a see-saw deal where it goes from net > charging to net discharging dozens of times per ride. Is that ok with > Li-Ion?
Most of what I know comes from playing with model airplanes, so take this all with grains-o-salt: On a charger that goes to 10.2V -- Eeek. Not on a model airplane you don't! Because model airplanes don't come with any of those wussy protection circuits -- people buy ammo boxes and fiberglass bags for battery charging for a REASON, and they post YouTube movies and RC Groups pictures of burning airplanes for roughly the same reason. I suppose that if it's all part of a system designed for it it's OK. Just don't mix and match. Is this some anonymous Chinese company that sells stuff, that you'll never be able to sue if your house burns down, or is it a good old 'merican company with a good old 'merican address to which writs may be sent? If you want "safe" charging and aren't interested in learning how to design LiPo chargers, buy one designed for model airplanes off of Tower Hobbies (expensive but sue-able) or Hobby King (front-men for un-sue-able Chinese). Get a balancing charger. It could be that the battery pack has its own built-in balancing charger, and the 10.2V is just a more-or-less raw supply. As to charge/discharge: I had not heard about LiPo's not liking rapid charge/discharge, but then, you don't do that much with model airplanes. I _do_ know that LiPo's don't like heat, and like any other battery they get hot with high-current use. They don't like to charge as fast as they discharge. What REALLY makes a LiPo pack unhappy is lots of partial charge/discharge cycles without a balancing charger -- LiPo cells are very sensitive both to over charge and under charge, and a pack that's subject to a lot of partial cycles tends to get one cell that drifts toward too much charge and the other to too little. Modern chargers monitor each cell voltage and correct for this. If'n you're going to go there, I suggest using a charger that balances the cells, and something that protects from under- voltage (even if it means having the dynamo come on when you're huffing up a hill). HTH. Oh -- watch the pack for puffing; if it does put it someplace where it won't catch things on fire when it bursts into flame. The proper way to discard a suspicious pack, in order of the distance you live from the authorities, is to (1) toss it it salt water for 24 hours, then toss it in the trash; (2) pound a screwdriver through the center of the pack, let it burn off, then throw the remains away; (3) duct-tape it to a fence post and shoot at it until it burns, then proceed as (2). -- Tim Wescott Wescott Design Services http://www.wescottdesign.com I'm looking for work -- see my website!
On 2016-10-03 17:02, Tim Wescott wrote:
> On Mon, 03 Oct 2016 16:27:12 -0700, Joerg wrote: > >> Hi Folks, >> >> Just bought another Li-Ion deal with charger: >> >> https://images-na.ssl-images-amazon.com/images/I/41HL6Xmx1qL._SX466_.jpg >> >> The charger is like this little guy, a switcher that can deliver 1 amp: >> >> https://images-na.ssl-images-amazon.com/images/I/41HL6Xmx1qL._SX466_.jpg >> >> The typical battery is two cell bundles in series so 8.4V max. To my >> surprise the charger has 10.2V open loop voltage. It is not a switched >> deal to overcome wire resistance where it measures the battery voltage >> every once in a while. Just straight DC. It seems that it relies on the >> battery's "electric safety vent" to stop at 8.4V. Anybody seen this >> done? >> >> It's not a problem to build a proper charger that limits at 8.4V or >> ideally 200mV less. Because of cable resistance it'll be sluggish >> towards the end but I can leave it connected all night. Just puzzled >> that they do this. It's the same 10.2V on the system I already have, I >> just never measured. >> >> Other: I read several times that Li-Ion does not like fast charge >> discharge cycling like you have in a car. Yet one can buy Li-Ion car >> batteries now. Reason I ask is that I am thinking about reducing the >> size of a bicycle Li-Ion battery and using a dynamo to replenish. Given >> the hills around here that will be a see-saw deal where it goes from net >> charging to net discharging dozens of times per ride. Is that ok with >> Li-Ion? > > Most of what I know comes from playing with model airplanes, so take this > all with grains-o-salt: > > On a charger that goes to 10.2V -- Eeek. Not on a model airplane you > don't! Because model airplanes don't come with any of those wussy > protection circuits -- people buy ammo boxes and fiberglass bags for > battery charging for a REASON, and they post YouTube movies and RC Groups > pictures of burning airplanes for roughly the same reason. > > I suppose that if it's all part of a system designed for it it's OK. > Just don't mix and match. Is this some anonymous Chinese company that > sells stuff, that you'll never be able to sue if your house burns down, > or is it a good old 'merican company with a good old 'merican address to > which writs may be sent? >
It is from a seller in New York, fulfilled by Amazon. All comes from China, of course.
> If you want "safe" charging and aren't interested in learning how to > design LiPo chargers, buy one designed for model airplanes off of Tower > Hobbies (expensive but sue-able) or Hobby King (front-men for un-sue-able > Chinese). Get a balancing charger. >
Balancing would require hacking the battery packs for the middle contact, somthing I'd like to avoid.
> It could be that the battery pack has its own built-in balancing charger, > and the 10.2V is just a more-or-less raw supply. >
If does but at the same time that is also the defense of last resort. One of the batteries inadvertently opened when the rear tire on my mountain bike blew and sent some pieces scattering. There was a circuit board dangling of of the now disrobed battery pack.
> As to charge/discharge: I had not heard about LiPo's not liking rapid > charge/discharge, but then, you don't do that much with model airplanes. > I _do_ know that LiPo's don't like heat, and like any other battery they > get hot with high-current use. They don't like to charge as fast as they > discharge. >
It's not Li-Po like the RC guys use, it's Li-Ion like in laptop batteries. The cells used in manufacturing could sometimes actually be scavenged laptop cells. Nobody really knows but they do work nicely.
> What REALLY makes a LiPo pack unhappy is lots of partial charge/discharge > cycles without a balancing charger -- LiPo cells are very sensitive both > to over charge and under charge, and a pack that's subject to a lot of > partial cycles tends to get one cell that drifts toward too much charge > and the other to too little. Modern chargers monitor each cell voltage > and correct for this. If'n you're going to go there, I suggest using a > charger that balances the cells, and something that protects from under- > voltage (even if it means having the dynamo come on when you're huffing > up a hill). >
I think balancing is done at the pack. But probably by crude shunting as I did not see any inductors. The size would be selected large enough so it'll never deplete during a ride, even one where I have to throttle down for slowpokes. It just puzzled me when I read that Li-Ion doesn't like short-cycling.
> HTH. > > Oh -- watch the pack for puffing; if it does put it someplace where it > won't catch things on fire when it bursts into flame. The proper way to > discard a suspicious pack, in order of the distance you live from the > authorities, is to (1) toss it it salt water for 24 hours, then toss it > in the trash; (2) pound a screwdriver through the center of the pack, let > it burn off, then throw the remains away; (3) duct-tape it to a fence > post and shoot at it until it burns, then proceed as (2). >
:-) -- Regards, Joerg http://www.analogconsultants.com/
On 04.10.2016 01:27, Joerg wrote:
> Hi Folks, > > Just bought another Li-Ion deal with charger: > > https://images-na.ssl-images-amazon.com/images/I/41HL6Xmx1qL._SX466_.jpg > > The charger is like this little guy, a switcher that can deliver 1 > amp: > > https://images-na.ssl-images-amazon.com/images/I/41HL6Xmx1qL._SX466_.jpg > > The typical battery is two cell bundles in series so 8.4V max. To > my surprise the charger has 10.2V open loop voltage. It is not a > switched deal to overcome wire resistance where it measures the > battery voltage every once in a while. Just straight DC. It seems > that it relies on the battery's "electric safety vent" to stop at > 8.4V. Anybody seen this done?
Hi J�rg Not exactly the same, but I've seen a similar configuration in a Chinese MP3-playing toy. The configuration looked like: USB port -> 10 Ohm series resistor -> silicon diode -> LiPo battry. No other relevant components in the direct power path on the main board, but the battery did have a small protection board, apparently with the classic one chip and 2 transistor solution that seems to be common nowadays. The device in question did have an "interesting" quirk: When fully charged, it would fail to operate when the charger was disconnected. Switching it off and on with a (mechanical) switch would reset it. Apparently they indeed relied on the protection circuit to work as a simple ON/OFF charge controller. It would turn off on overvoltage and stay that way, so that when the charger was disconnected, the sharp voltage drop to zero (before the the protection has time to sense that the overload has gone away) would upset the main ASIC, which would get stuck somewhere in the wilderness of an improperly timed reset cycle. As for safety: There's a good reason to have control and protection circuits separate. A single fault condition can't normally kill both together (unless the protection is way inadequate). With only one power interrupting component (one MOSFET per direction of charge / discharge current flow) all it takes is a single fault in a semiconductor part to deadlock this thing into an always on charging condition, with a third party uncontrolled tolerance "nominally 5V" adapter for the power. Dimitrij
On 2016-10-04 16:05, Dimitrij Klingbeil wrote:
> On 04.10.2016 01:27, Joerg wrote: >> Hi Folks, >> >> Just bought another Li-Ion deal with charger: >> >> https://images-na.ssl-images-amazon.com/images/I/41HL6Xmx1qL._SX466_.jpg >> >> The charger is like this little guy, a switcher that can deliver 1 >> amp: >> >> https://images-na.ssl-images-amazon.com/images/I/41HL6Xmx1qL._SX466_.jpg >> >> The typical battery is two cell bundles in series so 8.4V max. To >> my surprise the charger has 10.2V open loop voltage. It is not a >> switched deal to overcome wire resistance where it measures the >> battery voltage every once in a while. Just straight DC. It seems >> that it relies on the battery's "electric safety vent" to stop at >> 8.4V. Anybody seen this done? > > Hi J�rg > > Not exactly the same, but I've seen a similar configuration in a Chinese > MP3-playing toy. The configuration looked like: > > USB port -> 10 Ohm series resistor -> silicon diode -> LiPo battry. > > No other relevant components in the direct power path on the main board, > but the battery did have a small protection board, apparently with the > classic one chip and 2 transistor solution that seems to be common > nowadays. > > The device in question did have an "interesting" quirk: When fully > charged, it would fail to operate when the charger was disconnected. > Switching it off and on with a (mechanical) switch would reset it. >
Probably because the battery's OVP had come and needed to be "unstuck".
> Apparently they indeed relied on the protection circuit to work as a > simple ON/OFF charge controller. It would turn off on overvoltage and > stay that way, so that when the charger was disconnected, the sharp > voltage drop to zero (before the the protection has time to sense that > the overload has gone away) would upset the main ASIC, which would get > stuck somewhere in the wilderness of an improperly timed reset cycle. >
A stuck ASIC would be poor design.
> As for safety: There's a good reason to have control and protection > circuits separate. A single fault condition can't normally kill both > together (unless the protection is way inadequate). With only one power > interrupting component (one MOSFET per direction of charge / discharge > current flow) all it takes is a single fault in a semiconductor part to > deadlock this thing into an always on charging condition, with a third > party uncontrolled tolerance "nominally 5V" adapter for the power. >
Single-fault safety is why I don't like the scheme where they use a higher external voltage. I can build a supply with exactly 8.2V but I tried that and it has one major disadvantage: As the battery voltage approaches 8.2V the charge current will become very small due to cable resistance. It'll take all day to recharge a battery to a reasonable level. That would present a minor inconvencience if I did a long ride late into the evening and wanted to head out again in the morning. For safety I ride with bright daytime lights. A scheme that would work but I haven't seen it implemented is this: Apply a current limited 10-12V externally and have the control electronics in the supply disconnect it every few seconds. Check open circuit voltage of the connected Li-Ion battery, if less than target voltage apply another burst. If at target voltage stop and signal a green LED for "charge is complete". If I wanted to do this right it'll be another electronics project and my hobby time is already occupied with bicycling and beer brewing. Maybe with a uC but as an analog guys I am not a great programmer. So possibly I'll do it analog. -- Regards, Joerg http://www.analogconsultants.com/
On Thu, 06 Oct 2016 12:54:34 -0700, Joerg wrote:

> On 2016-10-04 16:05, Dimitrij Klingbeil wrote: >> On 04.10.2016 01:27, Joerg wrote: >>> Hi Folks, >>> >>> Just bought another Li-Ion deal with charger: >>> >>> https://images-na.ssl-images-amazon.com/images/
I/41HL6Xmx1qL._SX466_.jpg
>>> >>> The charger is like this little guy, a switcher that can deliver 1 >>> amp: >>> >>> https://images-na.ssl-images-amazon.com/images/
I/41HL6Xmx1qL._SX466_.jpg
>>> >>> The typical battery is two cell bundles in series so 8.4V max. To >>> my surprise the charger has 10.2V open loop voltage. It is not a >>> switched deal to overcome wire resistance where it measures the >>> battery voltage every once in a while. Just straight DC. It seems that >>> it relies on the battery's "electric safety vent" to stop at 8.4V. >>> Anybody seen this done? >> >> Hi Jörg >> >> Not exactly the same, but I've seen a similar configuration in a >> Chinese MP3-playing toy. The configuration looked like: >> >> USB port -> 10 Ohm series resistor -> silicon diode -> LiPo battry. >> >> No other relevant components in the direct power path on the main >> board, >> but the battery did have a small protection board, apparently with the >> classic one chip and 2 transistor solution that seems to be common >> nowadays. >> >> The device in question did have an "interesting" quirk: When fully >> charged, it would fail to operate when the charger was disconnected. >> Switching it off and on with a (mechanical) switch would reset it. >> >> > Probably because the battery's OVP had come and needed to be "unstuck". > > >> Apparently they indeed relied on the protection circuit to work as a >> simple ON/OFF charge controller. It would turn off on overvoltage and >> stay that way, so that when the charger was disconnected, the sharp >> voltage drop to zero (before the the protection has time to sense that >> the overload has gone away) would upset the main ASIC, which would get >> stuck somewhere in the wilderness of an improperly timed reset cycle. >> >> > A stuck ASIC would be poor design. > > >> As for safety: There's a good reason to have control and protection >> circuits separate. A single fault condition can't normally kill both >> together (unless the protection is way inadequate). With only one power >> interrupting component (one MOSFET per direction of charge / discharge >> current flow) all it takes is a single fault in a semiconductor part to >> deadlock this thing into an always on charging condition, with a third >> party uncontrolled tolerance "nominally 5V" adapter for the power. >> >> > Single-fault safety is why I don't like the scheme where they use a > higher external voltage. I can build a supply with exactly 8.2V but I > tried that and it has one major disadvantage: As the battery voltage > approaches 8.2V the charge current will become very small due to cable > resistance. It'll take all day to recharge a battery to a reasonable > level. That would present a minor inconvencience if I did a long ride > late into the evening and wanted to head out again in the morning. For > safety I ride with bright daytime lights. > > A scheme that would work but I haven't seen it implemented is this: > Apply a current limited 10-12V externally and have the control > electronics in the supply disconnect it every few seconds. Check open > circuit voltage of the connected Li-Ion battery, if less than target > voltage apply another burst. If at target voltage stop and signal a > green LED for "charge is complete". > > If I wanted to do this right it'll be another electronics project and my > hobby time is already occupied with bicycling and beer brewing. Maybe > with a uC but as an analog guys I am not a great programmer. So possibly > I'll do it analog.
"proper" charging of a LiPo is 4.2V/cell (or whatever the pack calls for) or some maximum current, whichever is lower. Much like lead-acid, except with more potential for flame. The pack _should_ charge at maximum current until it hits 4.2V/cell, then stay there with the battery determining the current, then finally the charge should terminate when the current drops to some fraction of the cell's maximum current (IIRC 1/10th is the rule of thumb, but don't go designing a charger based on that). -- Tim Wescott Wescott Design Services http://www.wescottdesign.com I'm looking for work -- see my website!
On 2016-10-06 13:32, Tim Wescott wrote:
> On Thu, 06 Oct 2016 12:54:34 -0700, Joerg wrote: > >> On 2016-10-04 16:05, Dimitrij Klingbeil wrote: >>> On 04.10.2016 01:27, Joerg wrote: >>>> Hi Folks, >>>> >>>> Just bought another Li-Ion deal with charger: >>>> >>>> https://images-na.ssl-images-amazon.com/images/ > I/41HL6Xmx1qL._SX466_.jpg >>>> >>>> The charger is like this little guy, a switcher that can deliver 1 >>>> amp: >>>> >>>> https://images-na.ssl-images-amazon.com/images/ > I/41HL6Xmx1qL._SX466_.jpg >>>> >>>> The typical battery is two cell bundles in series so 8.4V max. To >>>> my surprise the charger has 10.2V open loop voltage. It is not a >>>> switched deal to overcome wire resistance where it measures the >>>> battery voltage every once in a while. Just straight DC. It seems that >>>> it relies on the battery's "electric safety vent" to stop at 8.4V. >>>> Anybody seen this done? >>> >>> Hi Jörg >>> >>> Not exactly the same, but I've seen a similar configuration in a >>> Chinese MP3-playing toy. The configuration looked like: >>> >>> USB port -> 10 Ohm series resistor -> silicon diode -> LiPo battry. >>> >>> No other relevant components in the direct power path on the main >>> board, >>> but the battery did have a small protection board, apparently with the >>> classic one chip and 2 transistor solution that seems to be common >>> nowadays. >>> >>> The device in question did have an "interesting" quirk: When fully >>> charged, it would fail to operate when the charger was disconnected. >>> Switching it off and on with a (mechanical) switch would reset it. >>> >>> >> Probably because the battery's OVP had come and needed to be "unstuck". >> >> >>> Apparently they indeed relied on the protection circuit to work as a >>> simple ON/OFF charge controller. It would turn off on overvoltage and >>> stay that way, so that when the charger was disconnected, the sharp >>> voltage drop to zero (before the the protection has time to sense that >>> the overload has gone away) would upset the main ASIC, which would get >>> stuck somewhere in the wilderness of an improperly timed reset cycle. >>> >>> >> A stuck ASIC would be poor design. >> >> >>> As for safety: There's a good reason to have control and protection >>> circuits separate. A single fault condition can't normally kill both >>> together (unless the protection is way inadequate). With only one power >>> interrupting component (one MOSFET per direction of charge / discharge >>> current flow) all it takes is a single fault in a semiconductor part to >>> deadlock this thing into an always on charging condition, with a third >>> party uncontrolled tolerance "nominally 5V" adapter for the power. >>> >>> >> Single-fault safety is why I don't like the scheme where they use a >> higher external voltage. I can build a supply with exactly 8.2V but I >> tried that and it has one major disadvantage: As the battery voltage >> approaches 8.2V the charge current will become very small due to cable >> resistance. It'll take all day to recharge a battery to a reasonable >> level. That would present a minor inconvencience if I did a long ride >> late into the evening and wanted to head out again in the morning. For >> safety I ride with bright daytime lights. >> >> A scheme that would work but I haven't seen it implemented is this: >> Apply a current limited 10-12V externally and have the control >> electronics in the supply disconnect it every few seconds. Check open >> circuit voltage of the connected Li-Ion battery, if less than target >> voltage apply another burst. If at target voltage stop and signal a >> green LED for "charge is complete". >> >> If I wanted to do this right it'll be another electronics project and my >> hobby time is already occupied with bicycling and beer brewing. Maybe >> with a uC but as an analog guys I am not a great programmer. So possibly >> I'll do it analog. > > "proper" charging of a LiPo is 4.2V/cell (or whatever the pack calls for) > or some maximum current, whichever is lower. Much like lead-acid, except > with more potential for flame. > > The pack _should_ charge at maximum current until it hits 4.2V/cell, then > stay there with the battery determining the current, then finally the > charge should terminate when the current drops to some fraction of the > cell's maximum current (IIRC 1/10th is the rule of thumb, but don't go > designing a charger based on that). >
Ideally yes but for expedient charging this requires sense lines to the battery pack which, on a bicycle, you don't have. -- Regards, Joerg http://www.analogconsultants.com/
Den torsdag den 6. oktober 2016 kl. 23.28.41 UTC+2 skrev Joerg:
> On 2016-10-06 13:32, Tim Wescott wrote: > > On Thu, 06 Oct 2016 12:54:34 -0700, Joerg wrote: > > > >> On 2016-10-04 16:05, Dimitrij Klingbeil wrote: > >>> On 04.10.2016 01:27, Joerg wrote: > >>>> Hi Folks, > >>>> > >>>> Just bought another Li-Ion deal with charger: > >>>> > >>>> https://images-na.ssl-images-amazon.com/images/ > > I/41HL6Xmx1qL._SX466_.jpg > >>>> > >>>> The charger is like this little guy, a switcher that can deliver 1 > >>>> amp: > >>>> > >>>> https://images-na.ssl-images-amazon.com/images/ > > I/41HL6Xmx1qL._SX466_.jpg > >>>> > >>>> The typical battery is two cell bundles in series so 8.4V max. To > >>>> my surprise the charger has 10.2V open loop voltage. It is not a > >>>> switched deal to overcome wire resistance where it measures the > >>>> battery voltage every once in a while. Just straight DC. It seems that > >>>> it relies on the battery's "electric safety vent" to stop at 8.4V. > >>>> Anybody seen this done? > >>> > >>> Hi Jörg > >>> > >>> Not exactly the same, but I've seen a similar configuration in a > >>> Chinese MP3-playing toy. The configuration looked like: > >>> > >>> USB port -> 10 Ohm series resistor -> silicon diode -> LiPo battry. > >>> > >>> No other relevant components in the direct power path on the main > >>> board, > >>> but the battery did have a small protection board, apparently with the > >>> classic one chip and 2 transistor solution that seems to be common > >>> nowadays. > >>> > >>> The device in question did have an "interesting" quirk: When fully > >>> charged, it would fail to operate when the charger was disconnected. > >>> Switching it off and on with a (mechanical) switch would reset it. > >>> > >>> > >> Probably because the battery's OVP had come and needed to be "unstuck". > >> > >> > >>> Apparently they indeed relied on the protection circuit to work as a > >>> simple ON/OFF charge controller. It would turn off on overvoltage and > >>> stay that way, so that when the charger was disconnected, the sharp > >>> voltage drop to zero (before the the protection has time to sense that > >>> the overload has gone away) would upset the main ASIC, which would get > >>> stuck somewhere in the wilderness of an improperly timed reset cycle. > >>> > >>> > >> A stuck ASIC would be poor design. > >> > >> > >>> As for safety: There's a good reason to have control and protection > >>> circuits separate. A single fault condition can't normally kill both > >>> together (unless the protection is way inadequate). With only one power > >>> interrupting component (one MOSFET per direction of charge / discharge > >>> current flow) all it takes is a single fault in a semiconductor part to > >>> deadlock this thing into an always on charging condition, with a third > >>> party uncontrolled tolerance "nominally 5V" adapter for the power. > >>> > >>> > >> Single-fault safety is why I don't like the scheme where they use a > >> higher external voltage. I can build a supply with exactly 8.2V but I > >> tried that and it has one major disadvantage: As the battery voltage > >> approaches 8.2V the charge current will become very small due to cable > >> resistance. It'll take all day to recharge a battery to a reasonable > >> level. That would present a minor inconvencience if I did a long ride > >> late into the evening and wanted to head out again in the morning. For > >> safety I ride with bright daytime lights. > >> > >> A scheme that would work but I haven't seen it implemented is this: > >> Apply a current limited 10-12V externally and have the control > >> electronics in the supply disconnect it every few seconds. Check open > >> circuit voltage of the connected Li-Ion battery, if less than target > >> voltage apply another burst. If at target voltage stop and signal a > >> green LED for "charge is complete". > >> > >> If I wanted to do this right it'll be another electronics project and my > >> hobby time is already occupied with bicycling and beer brewing. Maybe > >> with a uC but as an analog guys I am not a great programmer. So possibly > >> I'll do it analog. > > > > "proper" charging of a LiPo is 4.2V/cell (or whatever the pack calls for) > > or some maximum current, whichever is lower. Much like lead-acid, except > > with more potential for flame. > > > > The pack _should_ charge at maximum current until it hits 4.2V/cell, then > > stay there with the battery determining the current, then finally the > > charge should terminate when the current drops to some fraction of the > > cell's maximum current (IIRC 1/10th is the rule of thumb, but don't go > > designing a charger based on that). > > > > Ideally yes but for expedient charging this requires sense lines to the > battery pack which, on a bicycle, you don't have. >
can't just use a four wire cable leaving only the wire from connector to cells (which I'd expect to be very short) unaccounted for? -Lasse
On 2016-10-06 14:49, Lasse Langwadt Christensen wrote:
> Den torsdag den 6. oktober 2016 kl. 23.28.41 UTC+2 skrev Joerg: >> On 2016-10-06 13:32, Tim Wescott wrote: >>> On Thu, 06 Oct 2016 12:54:34 -0700, Joerg wrote: >>> >>>> On 2016-10-04 16:05, Dimitrij Klingbeil wrote: >>>>> On 04.10.2016 01:27, Joerg wrote: >>>>>> Hi Folks, >>>>>> >>>>>> Just bought another Li-Ion deal with charger: >>>>>> >>>>>> https://images-na.ssl-images-amazon.com/images/ >>> I/41HL6Xmx1qL._SX466_.jpg >>>>>> >>>>>> The charger is like this little guy, a switcher that can deliver 1 >>>>>> amp: >>>>>> >>>>>> https://images-na.ssl-images-amazon.com/images/ >>> I/41HL6Xmx1qL._SX466_.jpg >>>>>> >>>>>> The typical battery is two cell bundles in series so 8.4V max. To >>>>>> my surprise the charger has 10.2V open loop voltage. It is not a >>>>>> switched deal to overcome wire resistance where it measures the >>>>>> battery voltage every once in a while. Just straight DC. It seems that >>>>>> it relies on the battery's "electric safety vent" to stop at 8.4V. >>>>>> Anybody seen this done? >>>>> >>>>> Hi Jörg >>>>> >>>>> Not exactly the same, but I've seen a similar configuration in a >>>>> Chinese MP3-playing toy. The configuration looked like: >>>>> >>>>> USB port -> 10 Ohm series resistor -> silicon diode -> LiPo battry. >>>>> >>>>> No other relevant components in the direct power path on the main >>>>> board, >>>>> but the battery did have a small protection board, apparently with the >>>>> classic one chip and 2 transistor solution that seems to be common >>>>> nowadays. >>>>> >>>>> The device in question did have an "interesting" quirk: When fully >>>>> charged, it would fail to operate when the charger was disconnected. >>>>> Switching it off and on with a (mechanical) switch would reset it. >>>>> >>>>> >>>> Probably because the battery's OVP had come and needed to be "unstuck". >>>> >>>> >>>>> Apparently they indeed relied on the protection circuit to work as a >>>>> simple ON/OFF charge controller. It would turn off on overvoltage and >>>>> stay that way, so that when the charger was disconnected, the sharp >>>>> voltage drop to zero (before the the protection has time to sense that >>>>> the overload has gone away) would upset the main ASIC, which would get >>>>> stuck somewhere in the wilderness of an improperly timed reset cycle. >>>>> >>>>> >>>> A stuck ASIC would be poor design. >>>> >>>> >>>>> As for safety: There's a good reason to have control and protection >>>>> circuits separate. A single fault condition can't normally kill both >>>>> together (unless the protection is way inadequate). With only one power >>>>> interrupting component (one MOSFET per direction of charge / discharge >>>>> current flow) all it takes is a single fault in a semiconductor part to >>>>> deadlock this thing into an always on charging condition, with a third >>>>> party uncontrolled tolerance "nominally 5V" adapter for the power. >>>>> >>>>> >>>> Single-fault safety is why I don't like the scheme where they use a >>>> higher external voltage. I can build a supply with exactly 8.2V but I >>>> tried that and it has one major disadvantage: As the battery voltage >>>> approaches 8.2V the charge current will become very small due to cable >>>> resistance. It'll take all day to recharge a battery to a reasonable >>>> level. That would present a minor inconvencience if I did a long ride >>>> late into the evening and wanted to head out again in the morning. For >>>> safety I ride with bright daytime lights. >>>> >>>> A scheme that would work but I haven't seen it implemented is this: >>>> Apply a current limited 10-12V externally and have the control >>>> electronics in the supply disconnect it every few seconds. Check open >>>> circuit voltage of the connected Li-Ion battery, if less than target >>>> voltage apply another burst. If at target voltage stop and signal a >>>> green LED for "charge is complete". >>>> >>>> If I wanted to do this right it'll be another electronics project and my >>>> hobby time is already occupied with bicycling and beer brewing. Maybe >>>> with a uC but as an analog guys I am not a great programmer. So possibly >>>> I'll do it analog. >>> >>> "proper" charging of a LiPo is 4.2V/cell (or whatever the pack calls for) >>> or some maximum current, whichever is lower. Much like lead-acid, except >>> with more potential for flame. >>> >>> The pack _should_ charge at maximum current until it hits 4.2V/cell, then >>> stay there with the battery determining the current, then finally the >>> charge should terminate when the current drops to some fraction of the >>> cell's maximum current (IIRC 1/10th is the rule of thumb, but don't go >>> designing a charger based on that). >>> >> >> Ideally yes but for expedient charging this requires sense lines to the >> battery pack which, on a bicycle, you don't have. >> > > can't just use a four wire cable leaving only the wire from connector > to cells (which I'd expect to be very short) unaccounted for? >
It voids any warranty and liability protection if you cut open the enclosure of the battery pack. There are no screws, it has to be cut and pried away. -- Regards, Joerg http://www.analogconsultants.com/
Den fredag den 7. oktober 2016 kl. 00.17.59 UTC+2 skrev Joerg:
> On 2016-10-06 14:49, Lasse Langwadt Christensen wrote: > > Den torsdag den 6. oktober 2016 kl. 23.28.41 UTC+2 skrev Joerg: > >> On 2016-10-06 13:32, Tim Wescott wrote: > >>> On Thu, 06 Oct 2016 12:54:34 -0700, Joerg wrote: > >>> > >>>> On 2016-10-04 16:05, Dimitrij Klingbeil wrote: > >>>>> On 04.10.2016 01:27, Joerg wrote: > >>>>>> Hi Folks, > >>>>>> > >>>>>> Just bought another Li-Ion deal with charger: > >>>>>> > >>>>>> https://images-na.ssl-images-amazon.com/images/ > >>> I/41HL6Xmx1qL._SX466_.jpg > >>>>>> > >>>>>> The charger is like this little guy, a switcher that can deliver 1 > >>>>>> amp: > >>>>>> > >>>>>> https://images-na.ssl-images-amazon.com/images/ > >>> I/41HL6Xmx1qL._SX466_.jpg > >>>>>> > >>>>>> The typical battery is two cell bundles in series so 8.4V max. To > >>>>>> my surprise the charger has 10.2V open loop voltage. It is not a > >>>>>> switched deal to overcome wire resistance where it measures the > >>>>>> battery voltage every once in a while. Just straight DC. It seems that > >>>>>> it relies on the battery's "electric safety vent" to stop at 8.4V. > >>>>>> Anybody seen this done? > >>>>> > >>>>> Hi Jörg > >>>>> > >>>>> Not exactly the same, but I've seen a similar configuration in a > >>>>> Chinese MP3-playing toy. The configuration looked like: > >>>>> > >>>>> USB port -> 10 Ohm series resistor -> silicon diode -> LiPo battry. > >>>>> > >>>>> No other relevant components in the direct power path on the main > >>>>> board, > >>>>> but the battery did have a small protection board, apparently with the > >>>>> classic one chip and 2 transistor solution that seems to be common > >>>>> nowadays. > >>>>> > >>>>> The device in question did have an "interesting" quirk: When fully > >>>>> charged, it would fail to operate when the charger was disconnected. > >>>>> Switching it off and on with a (mechanical) switch would reset it. > >>>>> > >>>>> > >>>> Probably because the battery's OVP had come and needed to be "unstuck". > >>>> > >>>> > >>>>> Apparently they indeed relied on the protection circuit to work as a > >>>>> simple ON/OFF charge controller. It would turn off on overvoltage and > >>>>> stay that way, so that when the charger was disconnected, the sharp > >>>>> voltage drop to zero (before the the protection has time to sense that > >>>>> the overload has gone away) would upset the main ASIC, which would get > >>>>> stuck somewhere in the wilderness of an improperly timed reset cycle. > >>>>> > >>>>> > >>>> A stuck ASIC would be poor design. > >>>> > >>>> > >>>>> As for safety: There's a good reason to have control and protection > >>>>> circuits separate. A single fault condition can't normally kill both > >>>>> together (unless the protection is way inadequate). With only one power > >>>>> interrupting component (one MOSFET per direction of charge / discharge > >>>>> current flow) all it takes is a single fault in a semiconductor part to > >>>>> deadlock this thing into an always on charging condition, with a third > >>>>> party uncontrolled tolerance "nominally 5V" adapter for the power. > >>>>> > >>>>> > >>>> Single-fault safety is why I don't like the scheme where they use a > >>>> higher external voltage. I can build a supply with exactly 8.2V but I > >>>> tried that and it has one major disadvantage: As the battery voltage > >>>> approaches 8.2V the charge current will become very small due to cable > >>>> resistance. It'll take all day to recharge a battery to a reasonable > >>>> level. That would present a minor inconvencience if I did a long ride > >>>> late into the evening and wanted to head out again in the morning. For > >>>> safety I ride with bright daytime lights. > >>>> > >>>> A scheme that would work but I haven't seen it implemented is this: > >>>> Apply a current limited 10-12V externally and have the control > >>>> electronics in the supply disconnect it every few seconds. Check open > >>>> circuit voltage of the connected Li-Ion battery, if less than target > >>>> voltage apply another burst. If at target voltage stop and signal a > >>>> green LED for "charge is complete". > >>>> > >>>> If I wanted to do this right it'll be another electronics project and my > >>>> hobby time is already occupied with bicycling and beer brewing. Maybe > >>>> with a uC but as an analog guys I am not a great programmer. So possibly > >>>> I'll do it analog. > >>> > >>> "proper" charging of a LiPo is 4.2V/cell (or whatever the pack calls for) > >>> or some maximum current, whichever is lower. Much like lead-acid, except > >>> with more potential for flame. > >>> > >>> The pack _should_ charge at maximum current until it hits 4.2V/cell, then > >>> stay there with the battery determining the current, then finally the > >>> charge should terminate when the current drops to some fraction of the > >>> cell's maximum current (IIRC 1/10th is the rule of thumb, but don't go > >>> designing a charger based on that). > >>> > >> > >> Ideally yes but for expedient charging this requires sense lines to the > >> battery pack which, on a bicycle, you don't have. > >> > > > > can't just use a four wire cable leaving only the wire from connector > > to cells (which I'd expect to be very short) unaccounted for? > > > > It voids any warranty and liability protection if you cut open the > enclosure of the battery pack. There are no screws, it has to be cut and > pried away.
but won't the wiring from whatever connector is on the battery pack to the cells inside the pack be very limited? -Lasse