brushless and A123 questions - Page 3 - RC-Monster Forums

BrianG · 10.17.2007, 03:13 PM

Sounds too risky to me. I think I'll stick to a more controlled CC/CV charge...

zeropointbug · 10.17.2007, 03:37 PM

Yeah, I'm sure they will survive it, but your cycle life would be way down to about that of lipo's, but that's just a guess... maybe it doesn't even effect it? After all, A123 HAS demonstrated a 5 min charge, although they used a pulse type charge, to get more mah into the cell.

highflier · 10.17.2007, 07:12 PM

All,
With the proper length of wire the charge rates are oK. Mine started at about 8 AMPs. There is a on going thred over at RCgroups about this. The tester is up over 100 charges and is yet to see any change in cell performance.

The Problem with using my NMHI charger is that they will never see the end of charge. thus if you do not watch closely the voltage will continue to climb way above 12 volts until the cell pops. Then it is toast. The benifit with the Zip charger is that no mater how long you leave it connected it will never climb above the votage of the deep cycle battery (13 volts or so), Also as it appoaches full charge the rate of charge slows down Mucho. Thus as long as you don't fall asleep it is unlikely that the voltage will get much above spec, and even if it does, it will only be slightly above spec and all reports I have read so far state, no damage done. Most say it would be bad to leave it for extended time but I have not read about any tests of that. keep in mind that the charge rate was down to 3 amps by the time the cell what 95% charged. It probably would have been below 2 before the cells were getting to 4 volts per.

All that said, Yes there is room for improvement. The charger works great, I would only ask for one thing. When the charge voltage reaches 11.5 volts to have it auto terminate.

Highflier

BrianG · 10.17.2007, 07:33 PM

Well, a simple high-current voltage regulator with a series resistor to limit the current would work too. As the battery reaches the voltage or the regulator, the current will drop accordingly. Or, a voltage regulator with a current regulator in series with the output. Set the V reg to the terminating battery voltate + the C reg drop-out voltage.

highflier · 10.19.2007, 12:19 AM

Yes CC CV charger would be the ideal solution. But this took minutes to create and cost next to nothing. Oh and it is so easy to make if you know how to use a wrie cutter and a soildering iron you can make it :)

I figured out my wire lengths.
I settled on 15' of 18 guage wire. A dead pack started at a charge of 12 amps but quickly droped to 8 amps and hovered theere for 15 min or so. at that time the voltage was 11.5 and I called it charged. Thus I can charge packs in 15 min. That is faster then the brushless E-maxx will discharge them. I am happy!!! Now I am looking forward to a new stadium brushless conversion.. It will use just a single 3s pack I Figure I will get about 10-15 of good run time per pack. I will be able to use 1 pack for 1/10 scale and 2 or 4 packs for the 1/8 monster truck.

Highflier

zeropointbug · 10.19.2007, 01:51 AM

Yes, but you also would want a decent charger to keep the lead acid batt topped up. As well, you would need a 12v battery in the first place, if not, you are paying at least $100 for a good deep cycle lead acid, at least I would want a deep cycle batt for that.

It's a fast way to charge at the very least though, and I don't know of a programmable power supply that can deliver 20 amps and charge 3s for under $200.

highflier · 10:59 AM

Ah, maybe I did not make myself clear. I use it with a deep cycle battery at a field. There is no electricity at the field.

My deep cycle came from Walmart. I think it was $80.00 But I use it as a source for my Lipo chargers also.

At home I use a PC converted P/S to powr my A123 compatible charger. It does not matter there if it takes a few hours to get all my cells charged up. When I use that I charge at 5 amps. Even though charger will handle up to 8.

I use a battery tender for the Deep cycle. I just connect it and forget it as it enters a maintaince mode once the deep cycle is fully charged. My deep cycle is going on 3 years now and it is not leting me down.

Highflier