H! I wonder how others with reverse eletric motor esp in BEC cars deal with voltage drop during reverese working?

I have an MNR Vortx in build, now driving, in process of first drives. There is a starter motor functioning as a reverese motor - engages to gear on propshaft and spins it reverese when switched.

Wiring is : battery (+) goes to main current FIA switch, other pole of this swich connetced to two cables - one to car engine etc normal wiring (Honda CBR 1000rr) , second - to this reverse motor .

Battery is 18Ah motorcyle battery.

Now I set engine gear to Neutral, clutch on, press reverese switch , reverese motor engages to gear on propshaft (spend hours to fit it properly and solid changing some MNR mounts) and car goes rear nice, but - car engine cuts off. While reverse on, voltage drops to 6,5 V. So thats propably why engine stops, its not enought for the ECu and ignition etc to work .

How do You deal with that huge rather load and currrent needed for reverse electric motor to drive a car with me inside (approx 500kg , 3,38 diff) . It must cause voltage drop, even with bigger battery?

Was thinking if adding second small battery , not connected to car wiring in other than charging cable switched on demand only manualy. This reverse I need just in case, but if I spent hours to properly mount it and alignt with gear on propshaft, would like to have , even knowns its additional weight, possible unit that can fail etc.

How to separate this eletric motor from main wiring?

Look at reducing the voltage drop (current draw) as one option? I ran a Honda 400 starter motor, geared favourably directly onto the propshaft. This did not drop the voltage enough for the ECU to complain (GSXR1000K2, standard ECU and loom). Look at what you're trying to achieve, for me it was just a reverse to get it through some silly MSA requirement that the car go backwards, but if you're backing up a hill you'll need the starter motor to be substantial, etc., not just a scrutineering pass in the paddock.

Look at a 2nd battery? A dedicated Li-Ion battery need not be that big, and certainly not heavy. Just wire it into a relay and a switch, though modern starter motors have much of that built in.

Look at why you need the reverse in the first place, is it a legal requirement, or something you feel you need to have. That need may not be as real as you believe.

Obviously you've discounted the mechanical gearbox, so you've got some grip on reality.

https://www.youtube.com/watch?v=wU6cBjgW1cY

Thanks! as for reason for reverse it was mainly that I never drove a car without one so wanted to have something to help with parking maneuvers etc or to got on track after spin, such situations. No need for regulations / law as it is not road registered car. So if there need to be reverse will be good it has as much power as possible for such (electric-starter motor) solution.
Yesteraday I tried more with it , on not perfectly flat graver it has enough power (was reversing with engine off ).
Guess will leave it as it is, just must be prepared that reversing takes some more time and plan it.

Give it some rpm's? Greater alternator output should help.

I guess there are two ways to cure this issue....

1) reduce the load: a smaller starter motor and/or a slower reverse speed

2) increase the supply: a larger battery with a higher rating

I think there is significant consensus that keeping the engine running isn't desirable - the voltage change can cause issues for some bike's ECUs, regulator etc. Presumably diodes can protect things but that's something to think about. My IVA inspector had obviously heard about issues and wouldn't reverse with the engine running.

One potential issue is that - assuming you want one - your reversing light will switch off as your starter motor reverse kicks in. I messed about with voltage regulators/capacitors before giving-up and fitting a teeny 12v RC battery specifically for the reversing light so that I could pass IVA.

If you are desperate for the engine to keep running, split charging and a second battery would definitely work - but very weighty for the benefit.

Better gearing = lower current. If it were me I'd go with a brushless DC and a high ratio box rather than hammer it is with a starter motor.

I suspect the voltage drop isn't really the issue (ECU should be compensated down to about 8v) but the inductive spikes from a huge current draw on a motor are likely to be unpleasant, but having the engine off only protects the electronics if they're physically disconnected by relays etc.

Or live without it.

15yrs/30'000+miles without and only miss it very occasionally (probably less the 25 times).

OK, you have to get used to pushing back into parking spaces when you either cant spot a drive through one or one with enough slope to roll back into. You get good at spotting no through road signs and gradients, enough yo roll on or too steep to push.
Only really bad one was going g UP the Stelvio and meeting a bus on a very short downhill section. Most of the issue was I'd pulled in so close to the 20' high wall, to try and make room for him, there wasn't room for me to get out, never mind push.

Having put it on for race regs/IVA, I’d rather not be without.
YouTube short

Decided to not change anything for now.
Will have reverse "just in case" after switch off engine. Try and learn how to live with BEC next season then decide .
Thanks for all opinions and sharing experiences !

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Originally posted by adithorp
Or live without it.

15yrs/30'000+miles without and only miss it very occasionally (probably less the 25 times).

OK, you have to get used to pushing back into parking spaces when you either cant spot a drive through one or one with enough slope to roll back into. You get good at spotting no through road signs and gradients, enough yo roll on or too steep to push.
Only really bad one was going g UP the Stelvio and meeting a bus on a very short downhill section. Most of the issue was I'd pulled in so close to the 20' high wall, to try and make room for him, there wasn't room for me to get out, never mind push.

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Not sure they *can* have a word, legally. Reverse isn't needed by law. Pushing a car is legally allowed and you wouldn't be reversing on a motorway or a place you can't get out safely.