Parallel Li-ion and Kudos LiFePO using Schottky?

[alban]

OK my latest brain convulsion for the Tonaro after reading around is to parallel a new £208 Kudos 36V 10AH LiFePO4 batt with my Li-ion 10AH with a 30A 60V dual Schottky diode from Maplins 30a-schottky to prevent reverse charging. This would theoretically give me 20Ah in toto and so a 25A draw would not be harmful as presumably each batt would stay below 20A draw. So I get increased range & torgue without over-stressing either batt?
Now the diode would heat up I believe so can I bolt a bit of Alu straight onto the diode using the hole in the body of the diode, as it's epoxy.
Seems cheaper than going 48V, I can use up the stock Li-ion, I buy British (sort of), keep the stock controller (maybe) and there's a warranty with the Kudos batt. Connect either by Kudos batt connector or dismantle and fit some other waterproof connector - what? That may invalidate any warranty tho'.
The only other prob I can foresee is that the Li-ion would drop Voltage quicker and then more current be drawn from the LiFePO4. But if I limit DOD to 80% I should keep it reasonably equal at 10-15A each. Occasionally check performance of Li-ion as it ages too.
Charge each separately.
Who's going to burst my bubble?!

Also - What about some kind of attachable cooling vanes on the motor? Are there such things? I want to be able to crawl up steep, long off road hills at 36V X 25A.

 

[wurly]

I don't see a problem with that. I'm using those diodes to link up to 4 lifepo4 batteries in parallel. Some are older therefore capacities will differ. Just keep an eye on range and don't discharge to lvc and you'll be fine. I would be careful of the connectors you intend using. You are drawing a lot of current the last section of wire/conectors going to the controller and the body of the diode will carry the 36V so beware of isolating the voltage. What size hills are you intending to climb? or are you just concerned with battery life?

 

[alban]

Thanks wurly.
My ambition is to get up some Welsh mountains - to go where the quad biker farmers go! Initially some Chiltern hills.
Do you mean ensuring that nothing shorts out on/around the diode? I was thinking of just soldering both + wires to the pins and covering with heatshrink. Tricky to ensure that the middle pin is connected and insulated as it will loop over the diode body and alu heatsink - was thinking about a ring connector soldered on.... The diode looks a bit flimsy. Have you gone for that sort and how have you done it? I'm not electrically-minded at all.
The small stock 15A controller is taking 20A OK at present but are you thinking it won't take the 25A due to heating up the solder tracks or something?

 

[Blew it]

alban, I appreciate your reasons for wishing to extend your range-per-charge by paralleling two batteries, but how is that narrow 8spd chain going to cope with the additional torque of a controller up-rated to 25A. Or for that matter, the bog standard rear cluster.

This is a fundamental problem with drive-through-the-chain systems. The chain and cog-sets are really only designed to cope with human only power, add motor assistance to that, and the life-span of the drive train components is reduced proportionately. I suppose the redeeming feature of such machines, is how quickly the rear wheel can be popped out to replace the cluster and chain, neither being particularly expensive items.

If you remember, I carried out some throttle-only test runs up a 12% hill in Swindon. After three ascents, the motor was very hot, not paint blistering stuff, but considerably hotter than would be experienced with a hub-motored machine. So yes, some cooling fins on the motor would probably be required.

Not for one moment am I going to insult your intelligence by suggesting you haven't thought about this. In fact, I can't think of a more enjoyable way of finding out just how much abuse these Tonaro machines can take.

I'm sure you will have a whole lot of fun finding out.

Hoping all goes well
Regards
Bob

 

[wurly]

I'll post a photo of how i connected mine up, later on. You'll need some heatsink compound for the diode also. PM me your address and i'll send some to you.

 

[Scottyf]

Arn't most standard cheap chains tested up to about 850kg of weight before they actually snap.
Thats almost the weight of a small car.

Most lightweight parts can take a bollocking before they give out. The motor at 25amp will cope with it fine. I'd be more worried about continuly pushing through 25amp up hills.

The trick to getting the motor and person to work well up hills is to get the motor to spin as fast as it can contunoly dropping the amp limit and increasing effciency and therefore less heat.

The motor will be fine and so will the chain and drive chain. Most bike parts even standard cheap ones will take alot of abuse.

If anything I would expect the Tonaro motor to take double its standard wattage without damaging anything.

Yes cooling will help but picking a low gear, get the motor spinning quickly and it will power up. Just remember the slower the motor turns with full throttle the more heat is generated.

You could always serial the batteries for a system that will spin very quickly. however I think you'd need a new controller for that.

 

[flecc]

It's not chain breaking that's necessarily the problem, its the high rate of sprocket and chain wear, and that is very real. The Bosch crank drive unit, which was rather more powerful than the Panasonic unit when it was introduced, quickly gained a reputation for destroying chains prematurely, worn out at three months being discussed in the German forums.

Those Panasonic and Bosch units are in the 400 to 500 watts gross power region, but here the Tonaro will have 900 watts gross plus any rider contribution, all through a narrow derailleur chain and sprockets. You can expect up to four to six times normal bike chain and sprocket wear rates, and the unit's gearbox bevel drive may object too.

All that aside, as Bob says, have fun!

 

[alban]

OK that's all interesting.
The bevel gear drive would be the really expensive part to fix if it wears out! I will not use it much at those power levels as it's leisure-only riding and only occasionally on such hills. Yes lowest gear and prob a rest now and then going up. Maybe a temperature warning device. Presumably heat is what knackers Halls so maybe I'll invest in a KU60 anyway to run sensorless if that is likely. Or is there worse - like melting summat else?
Anyone know of adjustable, fittable cooling vanes? The motor is a cylinder shape.
Edit: OK found these motor-cooling-fins

 

[Thamosy]

Hello. I'm new to the pedelec community and I'm searching for info on how (safely) to connect a couple of different LifePo4 in parallel so as to attack hills. I'd love it if you could let me have your wiring details.
Thanks

 

[Deleted member 4366]

Using diodes is the best way to do it because it covers some theoretical risks. I connected two different batteries in parallel, just by joining the power leads. It ran like that for about 9 months until the bike was sold. We only charged through one charge socket. The other battery then got charged through its power leads as the first one's voltage rose. Looking back, we should've kept kept both sockets and charged alternatively to keep both batteries' cells balanced. It worked anyway.

 

[Thamosy]

Thanks. I wonder though, would this be "relatively safe" with two very different Lipo4 batteries - different Ah and different age?

 

[Deleted member 4366]

All I can say is that it worked. The two batteries will always be at the same voltage because they're joined. To me, the only real risk is that if you get a short in one, it'll take the other with it, but shorts are pretty rare. If the BMS in one shut's off for any reason, all the current would have to come from the other. I think you'd notice the difference in performance, especially if you had a voltmeter to show the sag. You could then end up with batteries at different voltages, which might be a problem when the switched off BMS switches on again during charging. There'd be a rush while they equalised. I suppose there's a few theoretical things that could happen, but, there again, ours didn't get any of those problems.