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Avigo BMW I8 project. Need help with wiring 6v to 18v bypass circuit board

Posted: Tue Aug 23, 2016 4:11 pm
by SpeedyNYC
Hi Guys,

I'm customizing my son's AVIGO BMW I8 6 Volts. So far I added hand truck wheels, LED lights and another gearbox (added a few pics :D .) I want to convert to 18 Volts, but I'm having problems with the wiring. I have to bypass the circuit board or I will fried it. I saw three wiring diagrams here, but I'm not sure which one is the correct one for my setup . Can you guys give me a hand?

What's the difference between diagram 1 and 2? They look similar.

I bought a 12 volts 18Ah from Gruber, and I have the 6 volts 7ah that came with the car. Not sure if it's a good idea to use these batteries together.



Thanks :)

Re: Avigo BMW I8 project. Need help with wiring 6v to 18v bypass circuit board

Posted: Thu Aug 25, 2016 11:28 am
by SpeedyNYC
0 replies? :(
It's for my kid's safety that I'm asking for help here. I will appreciate if someone can give me a hand :D

Re: Avigo BMW I8 project. Need help with wiring 6v to 18v bypass circuit board

Posted: Thu Aug 25, 2016 2:41 pm
by Rob222
Batteries need to be the same AH to be hooked up in series.
Try viewtopic.php?f=21&t=20235. Cool 18v conversion board.
What's your kid in danger from ?

Re: Avigo BMW I8 project. Need help with wiring 6v to 18v bypass circuit board

Posted: Thu Aug 25, 2016 2:51 pm
by toycrusher
All 3 diagrams are essentially the same, just the artwork is different. As far as mixing AH on the batteries, it's not ideal but it's also not the end of the world. Just charge them separately with a smart charger after each use.

Re: Avigo BMW I8 project. Need help with wiring 6v to 18v bypass circuit board

Posted: Fri Aug 26, 2016 6:36 am
by Rob222
It is bad practice to connect batteries in series when they don't have the same capacity. The battery with the smaller capacity will be empty before the larger one, resulting in a lower voltage for the smaller battery. At that point things will start to get interesting as the larger battery will start to charge the smaller one through the connected circuit and with reversed voltage. The cell is not designed for being reversed and charged (while under a load) and bad things may happen : leaking acid, battery damage (and extreme case exploding). Neither of these situations are desirable. This is also the reason why most manuals of battery operated devices urge to replace all batteries at the same time.

Re: Avigo BMW I8 project. Need help with wiring 6v to 18v bypass circuit board

Posted: Fri Aug 26, 2016 8:49 am
by toycrusher
Rob222 wrote:It is bad practice to connect batteries in series when they don't have the same capacity. The battery with the smaller capacity will be empty before the larger one, resulting in a lower voltage for the smaller battery. At that point things will start to get interesting as the larger battery will start to charge the smaller one through the connected circuit and with reversed voltage. The cell is not designed for being reversed and charged (while under a load) and bad things may happen : leaking acid, battery damage (and extreme case exploding). Neither of these situations are desirable. This is also the reason why most manuals of battery operated devices urge to replace all batteries at the same time.
Rob is more correct. I have a pile of batteries I cycle through, all of varying ages and conditions and I don't keep track of which is which. I occasionally mismatch AH but it's never worse than a 7 and a 10. I haven't had anything bad happen but that doesn't mean it's not killing the smaller batteries and I just don't keep track to know.

Re: Avigo BMW I8 project. Need help with wiring 6v to 18v bypass circuit board

Posted: Fri Aug 26, 2016 8:57 am
by MR_Pat
I haven't had any issue running the smaller AH 6V in the 18 V set up but I also dont tend to leave the cars 18 v for more thn maybe an hour or so.. once i see the car slowing down i pul the 6v and my kids run the cars as the standard 12v they were .

Re: Avigo BMW I8 project. Need help with wiring 6v to 18v bypass circuit board

Posted: Fri Aug 26, 2016 11:10 am
by SpeedyNYC
Thank you so much guys for the input

I will try to exchange the 12v 18ah I bought from Gruber for a 12v 12ah.

I have a few more questions if you don't mind.

What's the normal temperature for a relay using this diagram? The two relays I installed get hot. Also, is this diagram the correct one to bypass the circuit board? I was told this unit can't handle more than 6volts.

Thank you again for your help,

Re: Avigo BMW I8 project. Need help with wiring 6v to 18v bypass circuit board

Posted: Fri Aug 26, 2016 12:53 pm
by MR_Pat
I dunno what to say about temperature i never really checked the relays after the kids were driving t hem at 18v. And i'm not familiar with your car . But i wired up my oldest ones safety first vette to avoid a board as well but i wired through the hi/lo/rv switch pedal and all to the motors. and i'm using CJB's Turbo timer . This is what I used . he still has the lights and sound controlled by the board as i left the power going to the board and all the wiring running to the lights . I just removed the boards control of the motors. Image

Re: Avigo BMW I8 project. Need help with wiring 6v to 18v bypass circuit board

Posted: Fri Aug 26, 2016 1:33 pm
by SpeedyNYC
The switches in the Avigo BMW I8 are all low current (6V). Not sure if by putting 18v directly hi/rv switch pedal could burn them.

Re: Avigo BMW I8 project. Need help with wiring 6v to 18v bypass circuit board

Posted: Fri Aug 26, 2016 4:02 pm
by toycrusher
Yes the 3 diagrams are the same except in this one you need to swap the 6v and 12v battery positions. The board only sees 6v, the motors see 18v when power is applied

Re: Avigo BMW I8 project. Need help with wiring 6v to 18v bypass circuit board

Posted: Sat Aug 27, 2016 1:28 am
by MR_Pat
keep the bigger 12v and just pick up a bigger ah 6v ... it will make for more run time.

Re: Avigo BMW I8 project. Need help with wiring 6v to 18v bypass circuit board

Posted: Mon Aug 29, 2016 6:37 am
by SpeedyNYC
Thanks for the replies :D

I returned the 12v 18ah to Gruber and bought a 12v 12ah and 6v 12ah. I will take some pics once I'm done putting everything together :D

Re: Avigo BMW I8 project. Need help with wiring 6v to 18v bypass circuit board

Posted: Wed May 02, 2018 1:21 pm
by Gmillere
SpeedyNYC could you share where you purchased those tires from? I want to buy a set to upgrade my Son's BMW I8