Hello all,

I have a micro rs4i it came with 5-cell 1200 mah NiMh batteries and I upgraded them to 6-cell 1300 mah NiMh and installed a Hobbywing EZRUN Brushless kit which comes with 7800kv motor and 25A ESC. But I am coping with multiple issues.

Since the batteries are fresh from the stock, I wanted to form charge them. Appearantly 0.1A or 0.2A Charging Rate (0.075C - 0.15C) misses peak detection (anyways I charged them for ~15 hours). At first charge at 0.075C batteries ended up at 8.25V (where they were meant to be around 8.45) then I discharged them at 0.1A. Although the charger says they are at 5.39V, voltmeter was saying they are at 7.2V (I think this is due to voltage drop during discharge)

Other than these, ESC Low voltage cutoff engages at 7.2V too no matter if I disable it or set it to 5.6V. So I thought there must be an issue with the freshness of the packs (huge drop of voltage under the load). For experiment purposes I tried to discharge the batteries at 1.0A for a while but discharge amperage got stuck on 0.7A. I am using Imax B6AC. Is my batteries faulty or is it my charger?


Thank you

Charge at 4 amps. Discharge at 20.

My charger supports 5.0A charging, 1.0A discharging. Can you explain the cause of your advice please?

Nimh packs like to be charged fairly quickly. By charging at such low amps you are not getting the cells to peak. The Esc is quite obviously still set with a lipo LVC activated if it is still cutting out with the pack at 7.2v. Investigate that further. When running with nicd/nimh the LVC should be switched off completely.

Also your charger has a Wattage limit on charge/discharge and so that's why it only reached 0.7A when discharging because P=IxV.

I am on the third cycle of the batteries now, I used 0.1A - 0.2A - 0.5A for these charges. Only 0.5A triggered peak detection so far. I looked for the voltages while discharges, they gradually go down from 8.4V to 7.2V in nearly an hour and drop to 5.4V in 2 minutes. Is this logical? (and they take up like 1050-1100mah, advertised was 1300)

Discharge power is rated as 5W so 5W/~8V=0.6Amps. Thank you for the explanation. I had not thought that it would be a limit for the situation.

4 amp charge rate? maybe on sub c cells, but not on a little 2/3a pack, thats just gonna cause them to vent. 2/3a cells typically like to be charged at 1 amp, you can push it up a little bit but they arent forgiving like a sub c nimh cell.

a nimh battery discharge curve is nothing like a lipo. when it has a load the voltage is going to drop quite a bit, even on a fresh charged battery. what you saw on the discharge cycle of 5.39v with a load and they went back to 7.2v when resting is normal.

basicly as i see it, you need to get that low voltage detection shut right off. if it still shuts the esc down what may be happening is the motor is pulling far more current than the pack can supply and the voltage is getting pulled far enough down to shut the esc or receiver down. in that case you have a couple options, either try going to a larger capacity nimh pack (like a 1600-1700mah) or bit the bullet and get some lipos.

Same store had 2000 mah cells too but they were double in price nonetheless. Also in fact, I do favor NiMh because it has its weight and adds an inertia to the micro rs4 but I think going LiPo will be my destiny since it has proper current supply by its discharge curve. Thank you for your support.

The discharge curve is not the biggest gain from nimh to lipo. If you are running subc cells (thats what the car is designed to hold so that makes sense to me, please check to see you are running subc size) then you need to up your charging rate, as much as 10 amps on a "bump" charge. Same for discharge. It may take a few cycles but you should see your voltage and mah both climb to where they should be. The major advantages imo of lipo are they are far less sensitive to bad charging habits and way longer runtimes.

I am on a stock chassis and AA batteries barely fit in a flat design. If I can get a pan chassis some day, I may go with subc cells. For now (as the car is going 60+ kmh with 7800kv motor which is ridicilous) i will get a lower kv (maybe ~5000kv) motor and hope for a decrease in current demand.

i think you missed the part were the OP said he was running a micro rs4

Yes, I tried with the lowest pinion gear (9T/58T), gives me 30 minutes runtime with 7800kv 200 size motor

OOOO yea..... never mind

I recently bought 2 GENS ACE 800 mah 2S Lipos (I will need to keep one charged, that bad in fact), they are total awesome compared to NiMhs that I own. Much lighter, much stable under load, much quicker to charge at the same price. Lightness means longer runtime too!