Noob alert: discharge/charging rates

[simon170]

Sorry for the noob question, but I havent had a modern charger/discharger unit in well over a decade and need some help...

Discharge:
My discharger has settings from 2 to 25volts and from 0.1 to 2 amps, what should I set these to? Do you just match the volts to the battery? Are there guide lines for what amps to use?

Charge:
I've been charging my packs at the same amps as their capacity (example: 4.2A for 4200mah pack) But one of them will only charge at 1.8A, dead battery?

Thanks for your help

[WIDELOAD]

What battery chemistry (Nicad, NIMH, Lipo etc.) you are using would help work it out.

[simon170]

I'm using NIMH at the moment, but I have Lipo's that I havent used yet.

Is this about to get confusing?

[WIDELOAD]

Not particularly...

Nimh Discharge: You want to discharge no lower than 0.9v/cell, so for a 7.2v 6cell nimh pack that would be 5.4v.
However due to the there not being a way to monitor individual cell voltage in a stick pack i wouldn't personally discharge the pack lower than 1v a cell (so 6v total for a 7.2v pack). This is to stop over-discharging any cells which will damage them, losing run time.
Have a read of this thread, it's got some good info in it: Nimh Discharging - RC Groups

Nimh charging: Charging them at their capacity rating (same as what you are doing) is charging them at 1C, that's perfectly fine. Charging at higher amps rates (eg. 4200 pack @ 5A) will give more performance at the start of the pack, but will give shorter run times. Charging at lower rates (4200 @ 3A) will take longer, have less 'punch' but will some times give longer runs times. Stick to 1C to keep everything simple.
As for the battery that will only charge at a lower rate regardless of what your set the amp rate too, it either means the pack is close to full when your are charging it (the charger will drop the amp rate when the battery is almost 'full'), or the pack is on its last legs or simply has high internal resistance. Therefore not able to take the higher amp rate, the charger has detected this as has dropped the amp rate accordingly.

Lipo charging: Use the lipo charge feature, set amp rate to suit capacity (same as you are doing with NIMH, eg. 2200mah-charge @ 2.2A). Make sure you use a balancer to ensure all the cells are equal in voltage.

Lipo discharging: Don't worry about it....Just run the packs to lipo cut off in your rig then charge them up. Make sure you never take a lipo lower than 3.2v/cell or you can damage the cells and potentially make it dangerous.

[simon170]

That's great, a real help, cheers pal

My voltage cutoff is set at 1v per cell, so that's a great relief.
Gonna stick with 1c, seems the safe option lol
Think the packs just had it from the sounds of it.

So does the fact my discharger lets me choose what amperage to use up the remaining juice not really matter?

[Manning]

Use your car to discharge the pack, don't waste the battery discharging it on the charger. There is exactly zero benefit.

[WIDELOAD]

Simon: Generally you would use the highest amp rate to discharge the pack that you can. My old race dis-charger used to be adjustable from 1-30amps. I only ever used around 10A at the most.

Manning: There is a benefit in discharging your Nicad & NIMH packs correctly. It removes the chance of the cells developing 'memory' (especially for Nicad...NIMHs don't get that much of a memory effect unless you abuse them), keeps the packs performing at their best for longer and can also can extend the life of packs before they are bin worthy. But most people don't care enough about their packs to do it properly and/or find it too hard to bother.

I will admit that for crawler/scaler/bashing use it isn't overly necessary unless you are gunning for the best performance etc. But even then that's what lipos are for.

[simon170]

Sorted, thanks dude

[Manning]

Originally Posted by WIDELOAD

Manning: There is a benefit in discharging your Nicad & NIMH packs correctly. It removes the chance of the cells developing 'memory' (especially for Nicad...NIMHs don't get that much of a memory effect unless you abuse them), keeps the packs performing at their best for longer and can also can extend the life of packs before they are bin worthy. But most people don't care enough about their packs to do it properly and/or find it too hard to bother.

I will admit that for crawler/scaler/bashing use it isn't overly necessary unless you are gunning for the best performance etc. But even then that's what lipos are for.

I disagree. Don't waste battery performance on a discharger. The battery has a finite # of charge/discharge cycles available, why waste it making heat?

The memory effect is the product of excellent marketing on the part of camcorder battery salesmen about 20 years ago, and it's been perpetuated by internet battery experts ever since (do you believe everything you read on the interweb?). According to a GE battery engineering manual that I used as a reference many years ago in my former career as a battery engineer at a military/aerospace facility, NiCds have to be charged and dishcharged EXACTLY the same (down to the second and at the exact same amperage) for many, many cycles to exhibit the effect. Then, one discharge cycle erases the memory. What people are blaming on the "memory effect" is the lackluster performance of craptastic consumer rechargeable batteries. No one can charge and discharge a RC battery in the exacting manner necessary to make the memory effect appear.

Take that for what it's worth.

[WIDELOAD]

I stand corrected in that case.
I was going by my experience and what i was taught & learned when i started in RC when hanging around at the track...Never had the 1:1 experience you've obviously picked up through your work. I just played with toy cars, and it always seemed to make a difference.

Now you said not to believe everything on the Net, but you just said that on the net....So I have to believe you???. j/k