May 092020

Recap (part 4)

Got wrong battery for ION, supercharged A979 with a new battery, got worried about it, crashed ION and broke it.

Wltoys A979-A LiPo-thoughts


Advertisement (box) says car has Li-Ion battery. Car came with a LiFe -battery. Ordered replacement is a LiPo -battery, but how does this matter?

LiPo -batteries are known for actually breaking if they’re discharged too much, but what actually is “too much”. After reading some articles it was common that the safe “cut-off” -point is above 3.0V/cell (most common was 3.3V), since <3.0V starts causing damage to the battery. But since the car came with LiFe -battery (and advertised Li-Ion)…

Fortunately there are audible alarms (LiPo Low Voltage Buzzer) that are plugged into the balance cable on a LiPo -battery and they go off when the cell voltage is too low, so I added that to my “these are needed” -list.

Original LiFe-battery runtime

The new charger has a nice feature which shows the current voltage in different cells (on LiFe & LiPo -batteries), and after running that 750mAh LiFe -battery dry, it showed 3.15V + 3.15V = 6.3V – and running LiPo -battery empty it showed the same voltage.

Nominal voltage on the original battery (printed on the side) is 6.4V – but LiFe -batteries are made out of series of 3.3V cells, so nominal voltage should be 6.6V…dunno, maybe they are 3.2V cells. And when LiFe-battery is full it would read 7.2V (3.6V/cell), minimum safe voltage is about 2.6-2.9V/cell, so that would be 5.2-5.8V.

At least this car has safety cut-off that cuts power just below the advertised nominal voltage of the attached LiFe-battery, instead of closer to the minimum safe voltage -area. No wonder the original battery runtime is a bit disappointing since power is cut off quite early, but might be on purpose since LiFe-battery voltage is quite constant until battery is empty.

Li-Ion/LiPo -compatibility

Since we have a cut-off at about 3.15V/cell, safety zone for LiPo is 3.0-3.3V and Li-Ion is 2.9-3.2V. This is quite close enough for LiPo, so Low Voltage Buzzer is unneeded in my opinion – as long as car is switched off and the battery is not drained any longer. And this device really enjoys being powered with LiPo.

ION temporary RWD-conversion

Since the car was not fun to drive as 3WD (steered hard when throttling/braking), I decided to disassemble it a bit and make it temporarily RWD by removing the other dogbone also from the front. Pair of pliers, detached steering link and suspension from their ball studs and removed dogbone. Connected everything back and now I had a “make a donut” -machine.

Part 4 <-> Part 6

Sorry, the comment form is closed at this time.