NiMH question

[Ashlandchris]

I've recently built a team c Jekyll with my son and installed a simple brushed motor and ESC from Absima. When I have test run it with LRP 4400mAh 7.2 stick pack the car is totally dying after a relatively short run. When I plug batteries in the charge they are showing 7.6-7.7 volts and when I charge at 1A they are going to approx 8.5v, but then only powering the car til they drop to 7.6ish. The steering is still working, but just no power for motor.
Is this normal? How long should a Nimh last on a full charge?

Any help gratefully received

[Danny]

Depends on the wind of the motor and what surface you've been running on, but a 4400 should generally last 10 minutes even on grass with a hot motor. When you say its dying does it noticably get slower or just suddenly cut off?

[VintageRacer]

Is it possible that your esc has a lipo cut off?

If so, your cells might be dropping below this on load, even though they are above voltage off load.

4400 mAh cells should last 10-15 minutes maybe more depending on the motor used

[pugs]

Originally Posted by Ashlandchris

I've recently built a team c Jekyll with my son and installed a simple brushed motor and ESC from Absima. When I have test run it with LRP 4400mAh 7.2 stick pack the car is totally dying after a relatively short run. When I plug batteries in the charge they are showing 7.6-7.7 volts and when I charge at 1A they are going to approx 8.5v, but then only powering the car til they drop to 7.6ish. The steering is still working, but just no power for motor.
Is this normal? How long should a Nimh last on a full charge?

Any help gratefully received

1A seams a little low charge rate, from a dead 4400mah battery it would take a long time to charge it about 4.4 hours....the charge rate should be around the same as lipo 1c so for your battery 4.4amps or lower. the way in which they charge is very different to a lipo. most decent chargers use delta peak voltage cut....basically the battery reaches a peak or max voltage under charge we'll say 10.04 volt for argument sake.... now when it reaches this max point the voltage actually starts to drop.....so it will hit 10.04 for example then as you keep charging it will drop to 10.03, 10.02 etc most chargers with delta peak will shut the battery off when it drops by around 0.04v....so in this case when the battery drops to 10.00v the charger will shut off as this is its fully charged point. on a temp charger i would say the battery would be around 38 degrees c....so quite warm really.....hope this helps

[Ashlandchris]

Hmm. Good suggestions.

ESC is an Absima ecu-1 which apparently can take lipos so I will look into whether it has a cut off.

I will also try charging at higher amperage see if it gives a little more punch.

I will time a full run to see length of run before power drops

[Ashlandchris]

Well, I tried again today with full charge batteries and they lasted approx 3mins. I had a spare 3300mah battery so tried that and it gave almost 15 mins so must be a battery issue. Will try discharge/ charge cycle and if that doesn't help it can go back to shop!!

[beale]

Sounds like there is a faulty cell

[neiloliver]

you are charging using a NiMH setting? If you had the charger on a Lithium setting then the voltage would be limited to 8.40V which is not suitable for NiMH which require charging at constant current.