Running garden tools on 40-60V DC instead of 120VAC?

I dread all those extension cords when using the hedge trimmer and other 
stuff. I found that if I connect the E-bike battery of a friend to it 
the hedge trimmer runs somewhat slower but reliably. It had 53V DC.

Those machines contain brush-type universal motors, probably with a 
compensation winding but not sure. Is is safe to run these with 40-60V 
DC over long periods of time or is there some sort of motor pathology 
that could hit?

If ok I could build a stack of 12-15 Li-Ion 18650 cells which, at 1.5A 
to 2A, should afford me about 45min of runtime. Or maybe build three 
sets of 4S or 5S batteries I could use for other stuff and then connect 
those in series when bushes need to be trimmed 2-3 times per year. With 
reverse-polarity protection diodes, of course, so I won't fry their 
individual BMS'es.

-- 
Regards, Joerg

http://www.analogconsultants.com/

On Monday, May 24, 2021 at 4:02:09 PM UTC-7, Joerg wrote:
> I dread all those extension cosrds when using the hedge trimmer and other 
> stuff. I found that if I connect the E-bike battery of a friend to it 
> the hedge trimmer runs somewhat slower but reliably. It had 53V DC. 
> 
> Those machines contain brush-type universal motors, probably with a 
> compensation winding but not sure. Is is safe to run these with 40-60V 
> DC over long periods of time or is there some sort of motor pathology 
> that could hit? 

If there is permanent magnet inside, then yes for wearing.

> If ok I could build a stack of 12-15 Li-Ion 18650 cells which, at 1.5A 
> to 2A, should afford me about 45min of runtime. Or maybe build three 
> sets of 4S or 5S batteries I could use for other stuff and then connect 
> those in series when bushes need to be trimmed 2-3 times per year. With 
> reverse-polarity protection diodes, of course, so I won't fry their 
> individual BMS'es. 

I would get an AC inverter.   48V DC to 120V AC can charge an EV as well.

tirsdag den 25. maj 2021 kl. 01.02.09 UTC+2 skrev Joerg:
> I dread all those extension cords when using the hedge trimmer and other 
> stuff. I found that if I connect the E-bike battery of a friend to it 
> the hedge trimmer runs somewhat slower but reliably. It had 53V DC. 
> 
> Those machines contain brush-type universal motors, probably with a 
> compensation winding but not sure. Is is safe to run these with 40-60V 
> DC over long periods of time or is there some sort of motor pathology 
> that could hit? 
> 
> If ok I could build a stack of 12-15 Li-Ion 18650 cells which, at 1.5A 
> to 2A, should afford me about 45min of runtime. Or maybe build three 
> sets of 4S or 5S batteries I could use for other stuff and then connect 
> those in series when bushes need to be trimmed 2-3 times per year. With 
> reverse-polarity protection diodes, of course, so I won't fry their 
> individual BMS'es. 

bite the bullet and buy a battery trimmer that runs on the same type of battery as your other tools

or something like this, https://www.amazon.com/Rockpals-250-Watt-Generator-Rechargeable-Emergency/dp/B075SSMR6K/6

In article <ih2pjaF8s8dU1@mid.individual.net>, 
news@analogconsultants.com says...
> 
> I dread all those extension cords when using the hedge trimmer and other 
> stuff. I found that if I connect the E-bike battery of a friend to it 
> the hedge trimmer runs somewhat slower but reliably. It had 53V DC.
> 
> Those machines contain brush-type universal motors, probably with a 
> compensation winding but not sure. Is is safe to run these with 40-60V 
> DC over long periods of time or is there some sort of motor pathology 
> that could hit?
> 
> 

There are 2 problems with that.  The motor needs to spin fast enough so 
the fan in it cools it off.  The other that may or may not be a factor 
is that brushes are selected for a current density.  That is the ammount 
of current determins the size of the brushes and too little is almost as 
bad as too much current as to the wear of the brushes.

On Monday, May 24, 2021 at 5:10:01 PM UTC-7, Ralph Mowery wrote:
> In article <ih2pja...@mid.individual.net>, 
> ne...@analogconsultants.com says...
> > 
> > I dread all those extension cords when using the hedge trimmer and other 
> > stuff. I found that if I connect the E-bike battery of a friend to it 
> > the hedge trimmer runs somewhat slower but reliably. It had 53V DC. 
> > 
> > Those machines contain brush-type universal motors, probably with a 
> > compensation winding but not sure. Is is safe to run these with 40-60V 
> > DC over long periods of time or is there some sort of motor pathology 
> > that could hit? 
> > 
> >
> There are 2 problems with that. The motor needs to spin fast enough so 
> the fan in it cools it off. The other that may or may not be a factor 
> is that brushes are selected for a current density. That is the ammount 
> of current determins the size of the brushes and too little is almost as 
> bad as too much current as to the wear of the brushes.

Also, DC tends to create spark and heat.  That's why Edison beat Tesla (the guy, not the car).

On Monday, May 24, 2021 at 4:59:37 PM UTC-7, lang...@fonz.dk wrote:
> tirsdag den 25. maj 2021 kl. 01.02.09 UTC+2 skrev Joerg: 
> > I dread all those extension cords when using the hedge trimmer and other 
> > stuff. I found that if I connect the E-bike battery of a friend to it 
> > the hedge trimmer runs somewhat slower but reliably. It had 53V DC. 
> > 
> > Those machines contain brush-type universal motors, probably with a 
> > compensation winding but not sure. Is is safe to run these with 40-60V 
> > DC over long periods of time or is there some sort of motor pathology 
> > that could hit? 
> > 
> > If ok I could build a stack of 12-15 Li-Ion 18650 cells which, at 1.5A 
> > to 2A, should afford me about 45min of runtime. Or maybe build three 
> > sets of 4S or 5S batteries I could use for other stuff and then connect 
> > those in series when bushes need to be trimmed 2-3 times per year. With 
> > reverse-polarity protection diodes, of course, so I won't fry their 
> > individual BMS'es.
> bite the bullet and buy a battery trimmer that runs on the same type of battery as your other tools 
> 
> or something like this, https://www.amazon.com/Rockpals-250-Watt-Generator-Rechargeable-Emergency/dp/B075SSMR6K/6

Well, i need 6 of them running in parallel, and with external electron tanks.  So, it's easier to build from scratch.

Joerg <news@analogconsultants.com> wrote:
> I dread all those extension cords when using the hedge trimmer and other 
> stuff. I found that if I connect the E-bike battery of a friend to it 
> the hedge trimmer runs somewhat slower but reliably. It had 53V DC.
> 
> Those machines contain brush-type universal motors, probably with a 
> compensation winding but not sure. Is is safe to run these with 40-60V 
> DC over long periods of time or is there some sort of motor pathology 
> that could hit?

It probably doesn't matter a damn in the end. If you really want to play 
it safe with what's likely a disposable tool anyways, reverse the polarity 
every battery charge so you get even brush wear. Just don't go too slow, 
or you'll overheat the motor- too much current, not enough cooling from 
whatever tiny fan is in there. Like with any appliance, there's not a 
single part in there that's overdesigned or built to do more than just get 
the job done.

> If ok I could build a stack of 12-15 Li-Ion 18650 cells which, at 1.5A 
> to 2A, should afford me about 45min of runtime. Or maybe build three 
> sets of 4S or 5S batteries I could use for other stuff and then connect 
> those in series when bushes need to be trimmed 2-3 times per year. With 
> reverse-polarity protection diodes, of course, so I won't fry their 
> individual BMS'es.

All that nonsense sound far more complex than a fucking extension cord, 
but hey, have fun. You're in the electrocution danger zone at 40-60 volts 
too. You won't be letting go of a DC tool running off some weird battery 
pack wrapped around your leg and arm.

On 5/24/2021 4:59 PM, Lasse Langwadt Christensen wrote:
> tirsdag den 25. maj 2021 kl. 01.02.09 UTC+2 skrev Joerg:
>> I dread all those extension cords when using the hedge trimmer and other
>> stuff. I found that if I connect the E-bike battery of a friend to it
>> the hedge trimmer runs somewhat slower but reliably. It had 53V DC.
>>
>> Those machines contain brush-type universal motors, probably with a
>> compensation winding but not sure. Is is safe to run these with 40-60V
>> DC over long periods of time or is there some sort of motor pathology
>> that could hit?
>>
>> If ok I could build a stack of 12-15 Li-Ion 18650 cells which, at 1.5A
>> to 2A, should afford me about 45min of runtime. Or maybe build three
>> sets of 4S or 5S batteries I could use for other stuff and then connect
>> those in series when bushes need to be trimmed 2-3 times per year. With
>> reverse-polarity protection diodes, of course, so I won't fry their
>> individual BMS'es.
> 
> bite the bullet and buy a battery trimmer that runs on the same type of battery as your other tools

+1

You're going to spend as much time and money trying to make a battery...
a commodity product that you can buy COTS mated to a specific trimmer.

> or something like this, https://www.amazon.com/Rockpals-250-Watt-Generator-Rechargeable-Emergency/dp/B075SSMR6K/6

Personally, I prefer long cords as they can meet many needs and
eliminate the need for batteries (that fail and might not have
sufficient charge for the work you've set out to do, TODAY!)
as well as keeping fuel on hand (for gas powered devices).

Battery powered power-washer?  Jackhammer?  Air compressor?

On 25/05/2021 01:13, Ed Lee wrote:
> On Monday, May 24, 2021 at 5:10:01 PM UTC-7, Ralph Mowery wrote:
>> In article <ih2pja...@mid.individual.net>,

>>> Those machines contain brush-type universal motors, probably with a
>>> compensation winding but not sure. Is is safe to run these with 40-60V
>>> DC over long periods of time or is there some sort of motor pathology
>>> that could hit?

>> There are 2 problems with that. The motor needs to spin fast enough so
>> the fan in it cools it off. The other that may or may not be a factor
>> is that brushes are selected for a current density. That is the ammount
>> of current determins the size of the brushes and too little is almost as
>> bad as too much current as to the wear of the brushes.
> 
> Also, DC tends to create spark and heat.  That's why Edison beat Tesla (the guy, not the car).

It's the other way round, I think you'll find - Tesla's AC beat Edison's DC.

-- 

Jeff

On 25/05/2021 09:02, Joerg wrote:
> I dread all those extension cords when using the hedge trimmer and other 
> stuff. I found that if I connect the E-bike battery of a friend to it 
> the hedge trimmer runs somewhat slower but reliably. It had 53V DC.
> 
> Those machines contain brush-type universal motors, probably with a 
> compensation winding but not sure. Is is safe to run these with 40-60V 
> DC over long periods of time or is there some sort of motor pathology 
> that could hit?

If you go much higher in voltage using DC on equipment designed for AC, 
then the on/off switch may arc for quite a while each time you turn it 
off, especially with an inductive field coil in series, and even more so 
at higher currents, like if you stall the motor and really want to turn 
it off. Same applies to fuses, if it has any. Perhaps 53V is still ok. 
Otherwise, a device that makes the current go to zero periodically (like 
an inverter) might help to extinguish any arc.