Hi Guys,

I was cleaning my car ready for KORT and i thought i would charge my 2700 AA battery pack to check everything was OK and whilst checking the brakes etc... i happened to notice the PT light getting very dim when i opperated any one of the servos... SAVOX 1256 jobies...
So i put a multimeter on the battery pack and i was astounded at the voltage drop if i opperated the brakes and the steering together.... which is 4 SAVOX 1265's operating.
So i fitted a old 4100 tornado battery pack and there was no appreciable problem.... well no more than 00.75 volt drop.
Has anyone else had this problem or was my 2700 battery pack a duffer...
however i did check each of the cells on the 2700 pack and they seem to be OK and have been properly cycled / charged etc...

Any Ideas.. Comments

John


Moved to the correct section RM.

Hi John, first of all get a helper or grow some more arms .. then operate the servo's and check your cells one at a time, I suspect you have a duff cell ..

Matt

John, i'm sure like Matt's says you've got a juff cell

Seriously, I have been concerned lately with the many drivers switching cell combinations and servos and the "odd" lapped missed.

It's been an issue in electric racing before that when applying a nanosecond of high current through the servo when crossing the loop is sufficient to drop the volts down below the lower limit and bang goes the transponder.

Do recommend drivers reading the various AMB articles on the does and don'ts about placing the transponders on your car.

I'm sure some smart electrical engineer will tell me I'm talking 5hite.

I checked my AA packs and i see next to no drop john
and i run 2 ace servos and 2 hitech for steering
maybe the savox servos pull more

The maximum continuous current draw for an AA pack is around 6-7 amps, so 4 1256's under load will soon start to exceed this & drag the voltage down.

A modern Sub C pack can deliver well over 30 amps without a problem whilst still holding voltage.

I use AA's in both my cars, logic tells me they should not work, but they do

if you need some more , try here john

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Thanks for the help guys,

The savox has a stall current drain of 5000mA each ! so with two of these stalling when the brakes are applied i can see could cause problems especially if you include some power drain for the steering and reciever and PT at the same time
When my little 2700AA pack is freshly charged i have goodish brakes.... after i have operated it for a couple of minutes the brakes dont work as well as they should... now if i pop on my old sub c cell pack there seems to be no problem..... would a LiPo or A123 cell set up sort this problem out.

John

i would say lipo better as its higher voltage although you would need a 6v regulater .the volts should still not drop below 6v as the lipo is 7.4volts so it should have plenty in reserve as its only letting 6v through. hope that makes sense also when i used to race electic touring cars we used to fit a power cap which stored power and when the servos,pt,motor drew a lot of current at same the battery dropped its voltage so the power cap then stepped in and its stored voltage used so all components had enough power

That's exactly why i never use AA batteries in any of my cars (and never have)

You don't need to go to sub c's to fix the problem, there's plenty of other battery sizes more suitable to our racing with suitable current rating/size. I use nimh 4/5 A size cells.

Ian

Where do you get your packs from ian or do you make them your self

this is the sort of thing im on about designed for 1/5 cars

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ian, what's this weeks racer tip? your banner is over a week old.....
is it 'run A size cells to be a winner' if you can afford them...

i'll change it later!!

Ian

Hi Guys;

Found a battery which is not too expensive @ £ 18 for the loose cells.... They are an A123 6.6v LiFe battery which is able to take realy savage and sustained amp draws from the savox servos.
They Recon 40c is OK for these cells and best of all they only take 15 mins to charge fully and apparently they dont go ......POP easily

All i gotta do now is build them up tonight .......... Kerboom ! !

Johnny