miss using 18vdc power tool batterys

[nota]

why because I have them, Li power tool batterys

used on a 12v rated El-bike
and a 24v lawnmower
batterys are ryobi 18v 4amp Li

both the bike and the mower run hot on 18v and heat the battery and wires
both came with lead acid 12v batterys [mower used 2 batterys] RATED AT 20 AMPS EACH
original lead/acid battery are DEAD and NEW replacements are HEAVY+cost
new Li batterys are costly at hundreds of $$$ each in the proper volts+amps

so I am trying to make the 18v 4 amp units I have work
would doubling the 18v Li batterys help them run cooler ?
to have 1/2 the current from each at 18v so 1/2 the draw current flow ?
will that affect the ''protection circuits'' in the power tool batterys ?

I have used the mower on 18v and the motor and wires are fine / not hot
but the batterys get hot say 140 deg f by the time they are used up
mower cuts and works ok but sometimes the battery gets so hot the thermal protection circuit cut out and I have to wait while it cools or switch batterys

the El bike I tryed last nite quickly over heated both the battery and melted my too small wires so the ride was short when I tryed the bike last nite but worked ok up to the point the battery quit [too hot]
plan is up size the wires and reduce the draw by using two batterys in parallel
to have 1/2 the current from each battery

btw the bike has a connector with one round 1/8'' post and a triangle slot also about
1/8'' anyone know where to get one to match needs a triangle post and a round hole

[aschen]

if you are asking if wiring the 2 18v batteries in parallel will make there life easier by reducing the current draw in half then the answer is definitely yes.

The batteries you have are probably in the range or 1-2 amp hours so 2-4 amp hours if wired in parallel. I assume you mean that the lead acid batteries are 20 amp hours rated so you would only have a small portion of the original capacity. Li-ion batteries have very low internal resistance and are capable of high burst currents.

I suspect your bigger problem is the 1.5 times nominal voltage. The current draw is going up by at least a similar factor, and power is going up 1.5^2. I think with the much reduced capacity and the increased current draw you probably won't get good results.

[nota]

yes the lead acid 12v battery was rated 20 amp/hours
the 18v Li are rated 4 amp/hours each but very lite so better for a bike

range was claim to 25 miles at 20 amps on the el-bike
so if I can get 8 miles out of 8 amps I will be happy
as the stores are only a mile or two away

over volts is not a big problem as it = more power
and both the mower was free and the El-bike was cheap
so no big deal if they burn up
Li battery's I am a bit more concerned about as they are also tool battery
and I would like to use them for some time
SO will hooking two 18v Li batterys in parallel affect the ''protection circuits'' built into the battery?

is the connector a common motorcycle battery connection ? with round and triangle plugs ?

[aschen]

The battery protection circuits should keep you from outright killing them. They may accelerate their normal natural degradation with continued high draw use. But in general they will not let themselves over discharge or over temp even when hooked in parallel. If you want to be extra careful I guess you could put a very big diode in series with each. I don't think that it is required however, I just wouldent hook a fully charged battery to a fully depleated one.

I think the range will not scale linearly with capacity because of the increased current draw as discussed. Also 4 amp hours is a big Li-on battery. The cells they use are generally less than 2 amp hours so if they are the connected 4 series (~16 Vish nominal) 2 parallel, they will have 8 cells total and probably have significantly less than 4 amp * hours per battery.

The manufactures are optimistic with their marketing of these things sometimes. There are some fascinating you tube channels where they test rated vs actual (see the you tube channel aVe, my favorite internet channel)

[nota]

yes I understand the Li deal with under/over charged cells
and the need for balance in charges

[dad911]

Use Hobby batteries. Cheap, universal charger. 3s = 12v, 6s=24v

https://hobbyking.com/en_us/batteries/lipo-batteries-all-brands.html

I would not put the ryobi batteries in parallel, they will not discharge evenly and may generate large currents internally trying to charge each other.

[aschen]

People run and even charge hobby batteries in parrellel all the time, it is fine. These are the lithium polymer packs as sudgested from hobbyking. The liFe round cells in tools are significantly more tolerant of abuse and in general a bit safer.

[nota]

Originally Posted by dad911

Use Hobby batteries. Cheap, universal charger. 3s = 12v, 6s=24v

https://hobbyking.com/en_us/batteries/lipo-batteries-all-brands.html

I would not put the ryobi batteries in parallel, they will not discharge evenly and may generate large currents internally trying to charge each other.

it was suggested to use large diodes to prevent that
doable as that would be part of the wiring on the unit not the battery
but if both full charged why should cross charging happen
they auto cutoff to prevent low volts [when the cross charging may happen]
worse case a bike or lawnmower it is not a big fire problem

batterys removed when stored or to recharge as they have other uses
and are likely low when use is over in the bike or mower

I like the ideal of multi use/roll batterys
and trying to make these 18 volt battery's I have work

[dad911]

Using 18v battery on 24v mower shouldn't hurt either, will just spin slower.

18v battery on 12v bike could hurt bike (50% overvoltage)

Do you know how much current bike draws under full load? If it is under 5 amp, something like this would work: https://smile.amazon.com/DROK-Waterproof-Synchronous-Converter-Adjustable/dp/B00CGSHR2S/ref=sr_1_1?ie=UTF8&qid=1506392433&sr=8-1&keywords=18v%2Bto%2B24%2Bv&th=1

[aschen]

Bike is likely in the 200 to 500 W peak motor range, so maybe as high as 50 amps at startup

[nota]

320w for two 160w motors at 12v dc one on each end of the shaft

any body know where to get the plug with a round 1/8'' and a triangle 1/8'' pins ?
one male one female on each side
similar plug with 2 round pins is called an SAE connector used on trailers
but of course my unit has a triangle pin+a round pin like a banana pin

[nota]

Originally Posted by aschen

Bike is likely in the 200 to 500 W peak motor range, so maybe as high as 50 amps at startup

will pedal starting reduced that load ?
how much do I need to wire for 10 gauge enuff ?

[nota]

Originally Posted by dad911

Using 18v battery on 24v mower shouldn't hurt either, will just spin slower.

18v battery on 12v bike could hurt bike (50% overvoltage)

Do you know how much current bike draws under full load? If it is under 5 amp, something like this would work: https://smile.amazon.com/DROK-Waterproof-Synchronous-Converter-Adjustable/dp/B00CGSHR2S/ref=sr_1_1?ie=UTF8&qid=1506392433&sr=8-1&keywords=18v%2Bto%2B24%2Bv&th=1

on line reports say the bike will live at 24v and go faster
so 18v Li [really 20v full charged to about 15v cutoff] should be fine

should be 320 watts at 12v =26+amps , but at 18v = under 20 amps

[aschen]

10 gauge should be fine, pedal assist will reduce the current draw in any case. Current is proportional to torque for a motor

If you increase the voltage to the motor, it will not decrease the current. It will go up by approximately in proportion. The power rating is a nominal type rating. IF it is producing 320W at 12v (12x26 amps) it will produce around 720w (18X40amps) at 18 volts. THis is for the full throttle condition as Im sure there is some sort of throttle voltage control. 720W is of course over the power rating of the motor which is why it could release its magic smoke if ran at full load continuously

It is common to reduce current by increasing voltage but this requires a different motor or a lower gear to reduce torque load.

[nota]

only if the motor runs twice as fast producing double the power

at 12v X 26+a = 320w
then the standard same work holds 320w divided by 18v = 16+ amps
by the way I learned el-tricks
I think/guess it will draw a bit more and run a bit faster but no where near 40a
maybe near 20 amps

[aschen]

The current is proportional to the torque and the speed is proportional to the voltage. So how the motor reacts depends on how it is loaded. The current of the motor isnt from the rpm its from the torque, but the increased voltage allows for increased current to flow (ohms law more or less). All this is going through a throttle control, depending on the motor and controller type (likely brushed dc), so if you have 18v going to the controller (which may fry it btw) at part throttle you can have substantially less at the motor.

However under full throttle full load if you double the voltage to the motor you will double the current and ~quadruple the power. You are also accelerating at 2x baseline by conservation of energy. Nominally at least, in reality it is worse because the motor is outside of spec and loses efficiency and basically turns into a heater.

320 watt rating is a completely nominal rating for the motor based on the company's confidence in it to produce power without blowing up. IF you put 100vdc into it and run it into a stall it will dissipate a few kilowatts as heat for a few seconds before it burns out.

Not trying to be argumentative on this, but backing out current from the power rating is the result of a fundamental missunderstanding of how motors work.

[nota]

this unit is pure on off
control is a micro switch to a relay in the battery box
so full speed or nothing
a golf cart type pulse speed control may be needed will see
the Li tool battery do fit snug in the battery box

I do appreciate you advice as most of my DC knowledge is 60's el shop
and racing slot cars I built motors for [from kit parts] still wild with silver wire and trick bits
cost was about the same as a real car junker but running back then

I have been reading a bit on the Li battery
lots of fear and BS on them on the net
but the boat and golfcart guy's like them

[aschen]

No worries. Since you just have a relay for simple control, things will be pretty easy on this side. This is one of those things where you may have to test how it works without worrying to much about the theory. You can try a couple brief "ons" to see if anything gets too hot. People are justified being a bit afraid of unprotected LI-polymer batteries, however tool batteries with their protections circuits intact are substantially smaller risk.

Here is how I would probably aproach: Start by wiring the motors is series and the batteries in parallel. I assume that the motors are typically in parallel for the 12v lead acid implementation. In series they will effectivly only see 9v each, so the performance will be much reduced. However lithium batteries have much lower internal resistance so it may not be as bad as you think. Drive around the neighborhood a bit like that and if you get ok performance, and milage, switch the motors back to parrellel and test again. I suspect this will work ok performance should be good, but things may get hot (some risk of letting the magic electronic smoke out of the motors or the relay), range might be a bit poor as well. Or everything may work just dandy, stop periodically to check for eccesive heat or burning smell.

[red-beard]

Why not use replacement LiFePo4 batteries? There are drop in replacements for most SLA batteries.

[nota]

Originally Posted by red-beard

Why not use replacement LiFePo4 batteries? There are drop in replacements for most SLA batteries.

COST

the mower was free
the bike very cheap
I had the power tool batterys and charger

a 20 amp Li battery is $230 I need 3 + a special charger

so spend almost a grand on batterys and a charger vs use what I have

plus I like messing with stuff
and the idea of reuse of stuff I have
without just buying more stuff