B25 Mitchell EP

After nearly two years the B25 may just get a maiden shortly. Although intended for two 4 cell 4000 lipo packs each powering their own motor, I am using 5 cells 3300 giving me in total around 1800 watts input power WOT. The extra cell also reduces current draw whilst increasing power available

I have a quandary after recent ground power tests. Identical batteries but one is about 10% down to it's mate, more obvious at high throttle. I am in a mind to parallel these packs, the joiner section will be an XT90 plug/socket therefore giving each motor the same input.

Will the difference make much to worry about and leave as is or go for the idea above? Got less than two days to decide..

Presumably your 'power tests' were with a watt-meter of some sort? Have you swapped motors and esc's to find out if they are different in order to firmly establish that it is the batteries? Have you measured RPM at the props?

If you are getting more power to one side, the model will not fly straight. You would need to adjust the ATV so that both sides give the same RPM at full throttle. And you'll need to adjust the throttle curve so that they both give the same rpm at partial throttle settings too.

Definitely the batteries, swapped them round using the watt meter in all scenarios. ESCs checked for timings, etc. The throttles are on independent channels ch3 and aux 3 so as you say Mike adjust the throttle curve so they generally match over a reasonable range is one option. The motors give out at full chat 800watt and 712 watts.

The reason I considered a patch together was for the better pack to make up for the lesser one. I know that invariably I will have to replace these packs, but they have had little use so maybe with more use they'll liven up.

Your choice on paralleling the batteries. I'm sure you won't over-discharge them in flight, so there is no real concern about the pack being out of balance.

If the batteries are discharging unequally, they could be charging unequally. So If you charge them individually and parallel them after resting, I'm wondering if you might create some initial heavy currents (and sparks when you join them) so suggest you consider charging them in parallel (including the balance ports of course)

I have employed this method for an electric bike pack (2p 10s pack with both 10s pack balance leads paralleled ) for over 3 years now without any problems.

Thanks Guys. I thought it best to parallel the packs then at least they are sharing the load Also, the motor/escs see the same voltage therefore theoretically the rpms should near enough if not equal. I date mark my Lipos and these where purchased early this year for the B25 and other than initial testing on the B25 they have not done much else at all. Possibly still settling in?

You have an iCharger, don't you? Check the internal resistance of the cells in each pack to see if there's a big difference.

I have checked the rpms and they are virtually similar. When I was originally monitoring the power I was only checking current/ wattage, so even though the amps being drawn, varied between motors in fact the efficiency of the ESCs and Motors gave similar actual rpms.

Checked both pack's cell's voltages and statuses. Pack 1 is down on cell volts. Put it on the i-Charger and cycled it from 3.7v to 4.2 a couple of times. Cells now come up to 4.19/4.2v. now shows 99% charge. 20.9 volts. That seems to have livened it up.

Made up a parallel lead anyway. Tried it on the parallel patch lead with no obvious difference. So, only way to find out what is what is to fly it.... :lol:

Far to technical for me,I'm sticking wth diesel

PhilF51 wrote: Checked both pack's cell's voltages and statuses. Pack 1 is down on cell volts. Put it on the i-Charger and cycled it from 3.7v to 4.2 a couple of times. Cells now come up to 4.19/4.2v. now shows 99% charge. 20.9 volts.

It's a lot easier to check the health of a battery by measuring the internal resistance.