ESC to compensate for battery voltage drop

steady_eddie · #1 23-09-2014

Is it possible that some ESC's can compensate for battery voltage drop by reducing power when the battery is in a good state?

i.e. with a 8.5T motor and freshly charged lipo's the car has good power and speed. As the batteries deplete the car runs too slow.

If I put a more powerful motor on the car would run at a good speed when the batteries are low but would be too powerful with fresh batteries.

So can any ESC give me consistent power throughout the battery cycle?

Fresh batteries will be 8.4v but near cutoff will be 6v so that's 30% difference in power as the batteries run down which is very noticeable on the track.

Dombrasky · #2 23-09-2014

sounds like new batteries needed imo,if there lipo`s they shouldn't drop that much,unless your running them right out
I havnt heard of an ESC that would do that tho

vrooom · #3 23-09-2014

You suppose not to run a car when car start to slow down. as this can damage a lipo by running it too low.

JonyNitro · #4 23-09-2014

Like above says it's down to your lipo " what lipo" you using in your sig? I would be looking to see if you can borrow a set just to check, but I'm sure the lipo are at fault 8.5 T s a low Turn so even a 30c lipo what be fine.

I use 3.4 as my LVC

steady_eddie · #5 23-09-2014

My Lipo cut-off is 3v - that's the only option for my ESC I believe. I don't have any reason to think there is anything wrong with the batteries but like all batteries the voltage drops as they become depleted - that's normal.

Even if the cut-off was 3.4v that would be 6.8v for 2s - compared to 8.4v newly charged that's still a 20% drop in power.

Do you not notice the car going faster with freshly charged lipo's?

Doesn't sound like any ESC has this feature anyway...

mattr · #6 23-09-2014

How long are you actually running to get all the way to LVC?
I can get ~20 minutes, give or take, out of my 2wd (8.5T, moderately sized batteries, 4200mAh, IIRC) before the LVC cuts in.

Performance between the race starting and finishing (or a 10 minute practice) is all but unnoticeable. Even running the 6.5 (or 5.5) in a 4wd........

If you are racing, it shouldn't be an issue (not many electric races over 10 minutes are there)
If you aren't racing, why are you bothered?

ANd FWIW, performance isn't just volts, you need a decent discharge rate too. A poorly C rated battery will have a more noticeable drop off in performance as voltage drops. I noticed that with the cheap arse batteries that came with my first RTR, 20/30C was the rating IIRC.

mattr · #7 23-09-2014

And what sort of ESC is it that has only one setting for LVC? A better ESC may mask any issues you are seeing, as it may be much more progressive/smoother at delivering power, and have less losses in the system.

steady_eddie · #8 23-09-2014

It's not (or was) not a cheap one - team Ansmann I think but don't have the model number, when I've looked it up it's still on sale for $130 so it's not cheap but I think it may be old, it came with the car I bought 2nd hand - is sensorless as well.

It's not a case of losses in the ESC - It's losses in battery voltage which is normal.

Doesn't anyone notice their car going faster with freshly charged batteries? Maybe newer ESC all have this feature already?

JonyNitro · #9 23-09-2014

I'm posh!!

I use SMC lipo the "Best" and never notice

3.0 is far to low!!

beale · #10 23-09-2014

You don't answer people's questions, how long are you running for to get your voltage down to 6 volts?
The whole advantage of lipo is a more consistent power output, I do notice a difference in second 5 minute heat from a non topped up pack but it's not as noticeable in lap times just the feel as you pull out of a slow corner.

ESC may not be cheap but technology moves on fast, I too set LVC at 3.4 as I look after my cells and don't like to stress them too much!!

Just for info I use Xerun V2.1 ESC and Turnigy 5300mah 50c packs so cheap really

Chequered Flag Racing · #11 23-09-2014

You may need to adjust your gearing if all is fine when the batteries are fully charged.

During your drive / race tell us if the following is happening

Are the batteries getting hot?
Is the motor getting hot and esc is cool?
Is the esc getting hot and the motor getting hot?

So what gearing are you using and which type of rear tyre?

mattr · #12 23-09-2014

Yes. I do notice the car getting slower, but the discharge curve on good lipos, with a good C rating is so flat that I have to run the car for bloody ages before its noticeable.

mattr · #13 23-09-2014

And no, there are no ESCs that compensate. They'd have to know how far you were going to run your battery down to........

tcboy1983 · #14 24-09-2014

Gm esc kind of have a function for racing after each run u put in how much u use out of the lipo and it try to keep the power the same and tries to keep the amps used the same But it a lot of farting around

even with new batteries u will notice performance drop as motors have kv ratings which is the rpm per volt so more volts more rpm
no matter what u do it will be the same as u use the lipo the voltage drops and rpm follows