Topic: 24v conversion issue - circuit overloading?

[Theojw71]

Hi, I have fitted the Porter 10 and Magura pot throttle I purchased from 4qd, to my Sinclair C5 (original 250watt motor).

The Magura's three wires are connected directly into the brown connector of the Porter 10 (in B,C,D as instructed) - I did not fit the optional 1KE resistors. Blue, yellow, red and black power cables purchased from 4qd are also fitted as instructed.

I have a LifePo4 30ah 24v battery which I purchased separately with a BMS fitted on it. On the live wire from the battery there is a blade fuse holder, with a 30amp fuse in it. I've endeavoured to ensure 6mm2 cable throughout the wiring as well.

On driving the C5, everything works fine for about 10-15 seconds, with full range of throttle control from the Magura, but then the 30amp blade fuse blows - clearly shows melted apart in the middle.

Can you advise me - should I just have a higher amp of fuse attached, for example, or would you recommend I don't need a fuse on the live connection? Alternatively, is there something else I have missed? The 4qd instructions looked pretty simple. I don't have many specs for the battery, as I bought it used rather than new.

Forgot to add, I tested the whole setup with the C5 jacked on bricks and no load (i.e. no-one in it) - it ran fine, for an extended period.

[Theojw71]

I'm confused now, because I swapped out the 30amp fuse holder and fitted a 70amp one. This time the C5 ran for longer, but when it cut out his time the 70amp fuse was still in one piece. Uh oh. I think I have blown something more substantial this time then in the Porter controller.

No idea what the cause can be. There's only a few components - motor, controller, Magura throttle and the battery and BMS.

[dansretropod]

Hi Theo,

Are you sure the battery doesn't have a high current cut out circuit? I had a 12v lifepo4 battery a while ago that had a built in cut out at about 80 amps. I sent it back to the battery maker and asked them to remove it.

[Theojw71]

Thanks Dan, that's a new avenue to investigate for me.

[jockywilson11]

Yep I've measured 89 amps on mine as a peak so it may well be that.

[Theojw71]

Dan, you're a genius - having left it a while, I tried again and again it drove, until the load increased a bit (slightly uphill and round a bend). Then it cut out again. That proves for me that (a) the wiring, controller and motor are OK, and (b) the throttle is working correctly too, so it has to be the battery and BMS.

Tried charging the Lifepo for a few hours in case it was at the threshold for capacity or something. Ran again, but again cut out after about 30 seconds driving.

So, the big question is, what do I do about it? Can anyone advise who I can show this Lifepo to, to get it sorted? It is the only component I didn't buy new or have full instructions for. Is there a LifePo expert in my region? (Wigan, North West)

[dansretropod]

That's great yep it does all point to the battery or BMS, glad its not your motor controller.  I don't really know enough about batteries and BMS's to be able to help you but I'm sure someone out there knows these sort of batteries inside out and can help.

Its an important note to anyone considering buying these lifepo batteries to double check they do not have this "safety" feature built in.

PS I finished and posted your 3D printed items today 1st class, let us know if you need and help with them

[jockywilson11]

Daft question - are you pedalling to move off? If it's cutting out that early it might just be you are hitting the limit too soon.

[Theojw71]

"Curiouser and Curiouser".

I just went back to the C5 in the shed, and tried the throttle again. Nothing. Then I pulled the maxi blade 70amp fuse I have on the live wire from the battery, checked it to ensure it was not blown, and stuck it back in. Re-tried the throttle and it came back to life straight away!

Some kind of short circuit maybe?

[Theojw71]

Just read your query, Jocky. Yes, pedalling off and being careful not to throttle too hard as well. Something eerier is at work. It's gutting for me as I'm at the amateur end of the spectrum where electronics are concerned.

I definitely need to buddy up with someone who knows their stuff about this specific battery and controller, to sort this out, I think.

[jockywilson11]

Just check all your connections, sounds like it may be nothing more than a loose wire, always worth a check.

[Theojw71]

Cheers Jocky - I will.

Thanks to Dan - my bits arrived in the post. I now have the 24v fan mounted and wired into the controller to motor wiring, so the fan engages only when I use the throttle, and spins in relation to the amount of power used.

I used a 120mm 24v 124CFM ball-bearing fan, if anyone's interested with IP55 waterproof rating. Great deal off ebay @ £19 including US postage.

http://www.ebay.co.uk/itm/170867285961?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

[Lancealot]

Instead of the lifepo batteries have you tried it with 2 standard lead batteries. They will not last as long but will see if you have other issues than the BMS.
I live north Manchester if that helps and i am an ex controls engineer. I have not got time next week but nay in a few weeks time to look.

ta lance

[Theojw71]

Much appreciated lance - I will take up the offer, as my pride and joy is all but ready to roll, and all I need to do is solve this power riddle.

[Theojw71]

Well, all, I finally found a link to give me the advice I needed about LifePo4 battery management systems. Here it is, hope it's of use to others.

http://goldenmotor.com/SMF/index.php?topic=4460.0