Forums

Car battery matching with alternator

Started by cameo October 28, 2014
On Wed, 29 Oct 2014 02:50:37 -0400, rickman <gnuarm@gmail.com> wrote:

>On 10/28/2014 9:24 PM, Jim Thompson wrote: >> On Tue, 28 Oct 2014 21:00:00 -0400, "Tom Miller" >> <tmiller11147@verizon.net> wrote: >> >>> >>> "Jasen Betts" <jasen@xnet.co.nz> wrote in message >>> news:m2pb7p$m36$1@gonzo.reversiblemaps.ath.cx... >>>> On 2014-10-28, Tim Wescott <seemywebsite@myfooter.really> wrote: >>>>> On Tue, 28 Oct 2014 11:03:27 -0700, cameo wrote: >>>> >>>>> >>>>> The car has a dingus called a "regulator" in it somewhere (these days >>>>> it's >>>>> usually built into the alternator). This holds the voltage from the >>>>> alternator to a reasonable value for battery charging, regardless of the >>>>> speed of the alternator, the condition of the battery, or the electrical >>>>> load. >>>> >>>> Actually the regulator doesn't control the voltage. The altenator is >>>> a current source, the regulator controls the current produced by the >>>> altenator, increasing the current when the battery is low, reducing it >>>> when it is full, the battery keeps the voltage stable. >>>> >>>> -- >>>> umop apisdn >>>> >>> >>> No, it is a constant voltage regulator with current limiting. Lead acid >>> batteries like to be charged with a negative temperature coefficient >>> compensated constant voltage. >>> >> >> The alternator _is_ a current source, _but_ it is a voltage-controlled >> current source, with a temperature compensation... >> >> <http://www.analog-innovations.com/SED/AlternatorRegulatorTC.pdf> > >Would that temperature compensation be the battery temperature? How is >that measured? Is it assumed that the battery temperature is the same >as the air in the engine compartment?
Yep, that is the assumption... a bad one. Back in the '60's, when I was designing alternator regulators for _all_ of the American car companies, I tried to get the sensing portion put at the battery, but the companies were too cheap... takes an extra wire :-( I did come up with an interesting scheme that could do remote sense _without_ an extra wire, but it was also deemed too expensive. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On Wed, 29 Oct 2014 09:03:02 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> Gave us:

>On Wed, 29 Oct 2014 02:50:37 -0400, rickman <gnuarm@gmail.com> wrote: > >>On 10/28/2014 9:24 PM, Jim Thompson wrote: >>> On Tue, 28 Oct 2014 21:00:00 -0400, "Tom Miller" >>> <tmiller11147@verizon.net> wrote: >>> >>>> >>>> "Jasen Betts" <jasen@xnet.co.nz> wrote in message >>>> news:m2pb7p$m36$1@gonzo.reversiblemaps.ath.cx... >>>>> On 2014-10-28, Tim Wescott <seemywebsite@myfooter.really> wrote: >>>>>> On Tue, 28 Oct 2014 11:03:27 -0700, cameo wrote: >>>>> >>>>>> >>>>>> The car has a dingus called a "regulator" in it somewhere (these days >>>>>> it's >>>>>> usually built into the alternator). This holds the voltage from the >>>>>> alternator to a reasonable value for battery charging, regardless of the >>>>>> speed of the alternator, the condition of the battery, or the electrical >>>>>> load. >>>>> >>>>> Actually the regulator doesn't control the voltage. The altenator is >>>>> a current source, the regulator controls the current produced by the >>>>> altenator, increasing the current when the battery is low, reducing it >>>>> when it is full, the battery keeps the voltage stable. >>>>> >>>>> -- >>>>> umop apisdn >>>>> >>>> >>>> No, it is a constant voltage regulator with current limiting. Lead acid >>>> batteries like to be charged with a negative temperature coefficient >>>> compensated constant voltage. >>>> >>> >>> The alternator _is_ a current source, _but_ it is a voltage-controlled >>> current source, with a temperature compensation... >>> >>> <http://www.analog-innovations.com/SED/AlternatorRegulatorTC.pdf> >> >>Would that temperature compensation be the battery temperature? How is >>that measured? Is it assumed that the battery temperature is the same >>as the air in the engine compartment? > >Yep, that is the assumption... a bad one. Back in the '60's, when I >was designing alternator regulators for _all_ of the American car >companies, I tried to get the sensing portion put at the battery, but >the companies were too cheap... takes an extra wire :-( > >I did come up with an interesting scheme that could do remote sense >_without_ an extra wire, but it was also deemed too expensive. > > ...Jim Thompson
Funny how now, they wouldn't hesitate to, and would even give a watertight line and term caps for it.
On Wed, 29 Oct 2014 09:03:02 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> Gave us:

>On Wed, 29 Oct 2014 02:50:37 -0400, rickman <gnuarm@gmail.com> wrote: > >>On 10/28/2014 9:24 PM, Jim Thompson wrote: >>> On Tue, 28 Oct 2014 21:00:00 -0400, "Tom Miller" >>> <tmiller11147@verizon.net> wrote: >>> >>>> >>>> "Jasen Betts" <jasen@xnet.co.nz> wrote in message >>>> news:m2pb7p$m36$1@gonzo.reversiblemaps.ath.cx... >>>>> On 2014-10-28, Tim Wescott <seemywebsite@myfooter.really> wrote: >>>>>> On Tue, 28 Oct 2014 11:03:27 -0700, cameo wrote: >>>>> >>>>>> >>>>>> The car has a dingus called a "regulator" in it somewhere (these days >>>>>> it's >>>>>> usually built into the alternator). This holds the voltage from the >>>>>> alternator to a reasonable value for battery charging, regardless of the >>>>>> speed of the alternator, the condition of the battery, or the electrical >>>>>> load. >>>>> >>>>> Actually the regulator doesn't control the voltage. The altenator is >>>>> a current source, the regulator controls the current produced by the >>>>> altenator, increasing the current when the battery is low, reducing it >>>>> when it is full, the battery keeps the voltage stable. >>>>> >>>>> -- >>>>> umop apisdn >>>>> >>>> >>>> No, it is a constant voltage regulator with current limiting. Lead acid >>>> batteries like to be charged with a negative temperature coefficient >>>> compensated constant voltage. >>>> >>> >>> The alternator _is_ a current source, _but_ it is a voltage-controlled >>> current source, with a temperature compensation... >>> >>> <http://www.analog-innovations.com/SED/AlternatorRegulatorTC.pdf> >> >>Would that temperature compensation be the battery temperature? How is >>that measured? Is it assumed that the battery temperature is the same >>as the air in the engine compartment? > >Yep, that is the assumption... a bad one. Back in the '60's, when I >was designing alternator regulators for _all_ of the American car >companies, I tried to get the sensing portion put at the battery, but >the companies were too cheap... takes an extra wire :-( > >I did come up with an interesting scheme that could do remote sense >_without_ an extra wire, but it was also deemed too expensive. > > ...Jim Thompson
This is why, as you say, it is a voltage driven current source. It will drive into the load only up to the max driving voltage of 14.8 VDC, OR the alternator's max design driving amperage at that voltage or below, whichever comes first. The added voltage actually places the battery under a charging state, and makes up for small cable drops as well. When all one has is 14.8 at the alternator terminals, minus cable drop, every half volt of that drop matters a bit. Long starter cables pose problems at times for that task too. That is why good, solid terminal connection cinching is one of the most important elements in power circuits and their connection and feed elements.
On 10/28/2014 11:24 AM, David Platt wrote:
>> I wonder what you think about the following problem: >> >> A car's battery needs to be replaced but the exact capacity battery is >> not available, though smaller or larger ones are. >> My feeling is that the battery capacity is matched by the manufacturer >> with the alternator's charging capacity, so the replacement battery >> should also closely match the OEM battery's capacity. >> Is my assumption correct, or it makes not much difference to use >> somewhat larger capacity replacement battery than the original? >> >> I'd appreciate reading your learned opinions. > > The matching of total battery capacity, to instantaneous maximum > charging current available from the alternator, is not as critical as > you seem to feel. > > Basically, the battery capacity is going to give you a measure of how > much starting power you can pull out of the battery (over a prolonged > period of cranking) before the voltage starts to drop. Larger is > (again, to a first approximation) better. > > Once you start the car, the charge control system (alternator and > control logic) is going to supply current to recharge the battery. > Typically, these systems are designed as (fairly crude) "constant > voltage" supplies - the alternator output is allowed to float upwards > to higher voltages, but is limited by the control system to no more > than around 14.4 volts (nominal). If the battery is heavily > discharged, the battery will draw about as much current as the > alternator can supply; the alternator's voltage won't reach 14.4 and > the limiting won't occur. Once the battery is largely recharged, its > terminal voltage will rise and it will draw less current from the > alternator, and the charge-control system will prevent the alternator > voltage from rising above 14.4 volts. > > If you put in a higher-capacity-than-before battery, then (if you > don't deep-discharge it) starting the car will draw out a smaller > proportion of the battery's stored charge. Its terminal voltage won't > drop as much as would be the case in a smaller battery. It'll > probably draw just about the same amount of recharge current as a > smaller battery would, though, and so the alternator won't really > "notice" a difference. > > Under conditions of really deep battery discharge, the higher-capacity > battery might be able to "take" more current than your present > alternator can supply. I don't believe this is harmful, though... the > alternator's output voltage will simply drop (due to e.g. resistive > loss in the alternator windings) and this will automatically reduce > the current into the battery to what the alternator is capable of > supplying. The same thing happens with your current battery, if the > vehicle is idling and the alternator isn't running very quickly... its > output voltage drops, the headlights dim a bit, and everything > balances out. > > Unless there's something really unusual about your car (I believe), > replacing an OEM battery with a new one having even twice the capacity > shouldn't present any sort of problem (other than the physical size of > the battery).
Thanks for that detailed explanation, as well as the less detailed ones from other respondents. My car's battery uses 24F terminals on the top. The old battery was an Interstate MT-24F model that had 600 CCA and 5 yr warranty. Because the same model was not in stock, I had it replaced with Interstate MTP-24F model, which has 800 CCA and has a 6 yr warranty. But is also 5 lbs heavier. BTW, the car is a 20-year old Honda Accord that still runs very well, despite the 320 K miles in it.
On 10/29/2014 12:03 PM, Jim Thompson wrote:
> On Wed, 29 Oct 2014 02:50:37 -0400, rickman <gnuarm@gmail.com> wrote: >> >> Would that temperature compensation be the battery temperature? How is >> that measured? Is it assumed that the battery temperature is the same >> as the air in the engine compartment? > > Yep, that is the assumption... a bad one. Back in the '60's, when I > was designing alternator regulators for _all_ of the American car > companies, I tried to get the sensing portion put at the battery, but > the companies were too cheap... takes an extra wire :-( > > I did come up with an interesting scheme that could do remote sense > _without_ an extra wire, but it was also deemed too expensive.
There is also the rule, "If it ain't broke, don't fix it!" The current method seems to work pretty well. What would the consumer get from a more accurate battery temperature measurement? -- Rick
On Wed, 29 Oct 2014 14:38:36 -0400, rickman <gnuarm@gmail.com> wrote:

>On 10/29/2014 12:03 PM, Jim Thompson wrote: >> On Wed, 29 Oct 2014 02:50:37 -0400, rickman <gnuarm@gmail.com> wrote: >>> >>> Would that temperature compensation be the battery temperature? How is >>> that measured? Is it assumed that the battery temperature is the same >>> as the air in the engine compartment? >> >> Yep, that is the assumption... a bad one. Back in the '60's, when I >> was designing alternator regulators for _all_ of the American car >> companies, I tried to get the sensing portion put at the battery, but >> the companies were too cheap... takes an extra wire :-( >> >> I did come up with an interesting scheme that could do remote sense >> _without_ an extra wire, but it was also deemed too expensive. > >There is also the rule, "If it ain't broke, don't fix it!" The current >method seems to work pretty well. What would the consumer get from a >more accurate battery temperature measurement?
Because of temperature mis-match most charging systems over- or under-charge the battery. Over-charging shortens battery life by overheating and water/electrolyte loss. "The current method" is still what I designed almost 50 years ago ;-) ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On 10/29/2014 2:49 PM, Jim Thompson wrote:
> On Wed, 29 Oct 2014 14:38:36 -0400, rickman <gnuarm@gmail.com> wrote: > >> On 10/29/2014 12:03 PM, Jim Thompson wrote: >>> On Wed, 29 Oct 2014 02:50:37 -0400, rickman <gnuarm@gmail.com> wrote: >>>> >>>> Would that temperature compensation be the battery temperature? How is >>>> that measured? Is it assumed that the battery temperature is the same >>>> as the air in the engine compartment? >>> >>> Yep, that is the assumption... a bad one. Back in the '60's, when I >>> was designing alternator regulators for _all_ of the American car >>> companies, I tried to get the sensing portion put at the battery, but >>> the companies were too cheap... takes an extra wire :-( >>> >>> I did come up with an interesting scheme that could do remote sense >>> _without_ an extra wire, but it was also deemed too expensive. >> >> There is also the rule, "If it ain't broke, don't fix it!" The current >> method seems to work pretty well. What would the consumer get from a >> more accurate battery temperature measurement? > > Because of temperature mis-match most charging systems over- or > under-charge the battery. > > Over-charging shortens battery life by overheating and > water/electrolyte loss. > > "The current method" is still what I designed almost 50 years ago ;-)
I think that is the point. It works plenty well enough so that I can't remember the last time I bought a battery. I just know my 17 year old truck is on its third battery.. well, fourth if you count the one that was replaced under warranty after just 3.5 years. There is no problem to solve, so don't try to fix it. -- Rick
On Wed, 29 Oct 2014 16:27:36 -0400, rickman <gnuarm@gmail.com> wrote:

>On 10/29/2014 2:49 PM, Jim Thompson wrote: >> On Wed, 29 Oct 2014 14:38:36 -0400, rickman <gnuarm@gmail.com> wrote: >> >>> On 10/29/2014 12:03 PM, Jim Thompson wrote: >>>> On Wed, 29 Oct 2014 02:50:37 -0400, rickman <gnuarm@gmail.com> wrote: >>>>> >>>>> Would that temperature compensation be the battery temperature? How is >>>>> that measured? Is it assumed that the battery temperature is the same >>>>> as the air in the engine compartment? >>>> >>>> Yep, that is the assumption... a bad one. Back in the '60's, when I >>>> was designing alternator regulators for _all_ of the American car >>>> companies, I tried to get the sensing portion put at the battery, but >>>> the companies were too cheap... takes an extra wire :-( >>>> >>>> I did come up with an interesting scheme that could do remote sense >>>> _without_ an extra wire, but it was also deemed too expensive. >>> >>> There is also the rule, "If it ain't broke, don't fix it!" The current >>> method seems to work pretty well. What would the consumer get from a >>> more accurate battery temperature measurement? >> >> Because of temperature mis-match most charging systems over- or >> under-charge the battery. >> >> Over-charging shortens battery life by overheating and >> water/electrolyte loss. >> >> "The current method" is still what I designed almost 50 years ago ;-) > >I think that is the point. It works plenty well enough so that I can't >remember the last time I bought a battery. I just know my 17 year old >truck is on its third battery.. well, fourth if you count the one that >was replaced under warranty after just 3.5 years. There is no problem >to solve, so don't try to fix it.
You clearly don't live in Arizona. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On 10/29/2014 1:27 PM, rickman wrote:
> On 10/29/2014 2:49 PM, Jim Thompson wrote: >> On Wed, 29 Oct 2014 14:38:36 -0400, rickman <gnuarm@gmail.com> wrote: >> >>> On 10/29/2014 12:03 PM, Jim Thompson wrote: >>>> On Wed, 29 Oct 2014 02:50:37 -0400, rickman <gnuarm@gmail.com> wrote: >>>>> >>>>> Would that temperature compensation be the battery temperature? >>>>> How is >>>>> that measured? Is it assumed that the battery temperature is the same >>>>> as the air in the engine compartment? >>>> >>>> Yep, that is the assumption... a bad one. Back in the '60's, when I >>>> was designing alternator regulators for _all_ of the American car >>>> companies, I tried to get the sensing portion put at the battery, but >>>> the companies were too cheap... takes an extra wire :-( >>>> >>>> I did come up with an interesting scheme that could do remote sense >>>> _without_ an extra wire, but it was also deemed too expensive. >>> >>> There is also the rule, "If it ain't broke, don't fix it!" The current >>> method seems to work pretty well. What would the consumer get from a >>> more accurate battery temperature measurement? >> >> Because of temperature mis-match most charging systems over- or >> under-charge the battery. >> >> Over-charging shortens battery life by overheating and >> water/electrolyte loss. >> >> "The current method" is still what I designed almost 50 years ago ;-) > > I think that is the point. It works plenty well enough so that I can't > remember the last time I bought a battery. I just know my 17 year old > truck is on its third battery.. well, fourth if you count the one that > was replaced under warranty after just 3.5 years. There is no problem > to solve, so don't try to fix it. >
What's wrong with incremental improvements over time? That's what the whole car industry has been doing ever since Henry Ford.
On 10/30/2014 2:13 PM, cameo wrote:
> On 10/29/2014 1:27 PM, rickman wrote: >> On 10/29/2014 2:49 PM, Jim Thompson wrote: >>> On Wed, 29 Oct 2014 14:38:36 -0400, rickman <gnuarm@gmail.com> wrote: >>> >>>> On 10/29/2014 12:03 PM, Jim Thompson wrote: >>>>> On Wed, 29 Oct 2014 02:50:37 -0400, rickman <gnuarm@gmail.com> wrote: >>>>>> >>>>>> Would that temperature compensation be the battery temperature? >>>>>> How is >>>>>> that measured? Is it assumed that the battery temperature is the >>>>>> same >>>>>> as the air in the engine compartment? >>>>> >>>>> Yep, that is the assumption... a bad one. Back in the '60's, when I >>>>> was designing alternator regulators for _all_ of the American car >>>>> companies, I tried to get the sensing portion put at the battery, but >>>>> the companies were too cheap... takes an extra wire :-( >>>>> >>>>> I did come up with an interesting scheme that could do remote sense >>>>> _without_ an extra wire, but it was also deemed too expensive. >>>> >>>> There is also the rule, "If it ain't broke, don't fix it!" The >>>> current >>>> method seems to work pretty well. What would the consumer get from a >>>> more accurate battery temperature measurement? >>> >>> Because of temperature mis-match most charging systems over- or >>> under-charge the battery. >>> >>> Over-charging shortens battery life by overheating and >>> water/electrolyte loss. >>> >>> "The current method" is still what I designed almost 50 years ago ;-) >> >> I think that is the point. It works plenty well enough so that I can't >> remember the last time I bought a battery. I just know my 17 year old >> truck is on its third battery.. well, fourth if you count the one that >> was replaced under warranty after just 3.5 years. There is no problem >> to solve, so don't try to fix it. >> > What's wrong with incremental improvements over time? That's what the > whole car industry has been doing ever since Henry Ford.
Nothing is wrong with incremental improvements. But what improvement is needed? Will this make the batter last longer? I've yet to read anything saying that. -- Rick