Battery Boost

[mart.hart]

I have a City Thunder which I guess is the same as a Wisper (Same wiring diagram)
Bike works great but when I tow the trailer it can run out of battery at about 10 miles.

Problem is the dog is fat and lame but we hate to leave him in kennels.
But peddling an electric bike with that lot in tow nearly saw me off when the battery died.

Is there a way of piggy backing another battery for when I tow the trailer, I guess a spare battery may be an idea but funds are a bit limited at the moment.

Thanks

Mart

 

[flecc]

Some have created an additional battery from small and cheaper rechargeable NiMh cells like AA or C size ones, coupling it in parallel via Schottky diodes to prevent cross transfer and destruction, but these don't extend the range very much, and under high loadings as in trailer pulling the additional battery might prove not really up to delivering enough power.

There's also the problem of organising charging for the 36 volt NiMh pack, this demanding the correct type of charger and a matching thermistor incorporated in the NiMh cell pack. By the time you'd made up and cased the battery and bought the new charger you could be half way to a new bike battery price but without a satisfactory result.

Alternatively 3 SLA (lead-acid) batteries with Schottky diodes would be simpler and not too expensive, but it would be a very heavy solution and the range extension wouldn't be great. Again you'd need a charger to suit.

It's a bitter pill to swallow with present battery prices, but a new one is really the best way to get a decent extension to your range.
.

 

[Fecn]

Some have created an additional battery from small and cheaper rechargeable NiMh cells like AA or C size ones, coupling it in parallel via Schottky diodes to prevent cross transfer and destruction, but these don't extend the range very much, and under high loadings as in trailer pulling the additional battery might prove not really up to delivering enough power.

When connected through schottky diodes though (old computer power supplies are an excellent source of high-current rated schottky diodes), both batteries will work in parallel, so the extra battery doesn't need to be capable of delivering as much current anyway. I would counter Flecc's claim that home-made extra batteries do not add much range, as my personal experiences have been good. My 12Ah home-made pack certianly outlasts my 10Ah original pack. I reckon it's all down to battery choice - If you want some absolute top-quality NiMH cells, get Duracell ones - They have massive current delivery and fast recharge times.... If you want cheap cells (like me) then buy yourself some Aldi 4Ah C-Cells. I made my 12Ah pack for less than £70 all-in.

 

[mart.hart]

When connected through schottky diodes though (old computer power supplies are an excellent source of high-current rated schottky diodes), both batteries will work in parallel, so the extra battery doesn't need to be capable of delivering as much current anyway. I would counter Flecc's claim that home-made extra batteries do not add much range, as my personal experiences have been good. My 12Ah home-made pack certianly outlasts my 10Ah original pack. I reckon it's all down to battery choice - If you want some absolute top-quality NiMH cells, get Duracell ones - They have massive current delivery and fast recharge times.... If you want cheap cells (like me) then buy yourself some Aldi 4Ah C-Cells. I made my 12Ah pack for less than £70 all-in.

That sounds great but I am a bit limited in the technical department.
I did a google but it brought me back here…..lol
Any links-dummies guides ?

Thanks

Mart

 

[torrent99]

That sounds great but I am a bit limited in the technical department.
I did a google but it brought me back here…..lol
Any links-dummies guides ?

Thanks

Mart

Not really...it's not a dummies thing! ( no offence intended)

There are basically 2 main problems you'll have to solve:
1) Joining the batteries together. Soldering them takes some skill as excess heat can easily damage them. Ideally you TIG (?) weld them with small strips of metal.
2) Then there's charging. It's not as easy as connect them to 36V (well 42V) and wait, you need to put thermistors in the right place to sense the sharp rise in temperature when the batteries are charged. And of course you need to source the NiMH charger cheaply...

So non-trivial I'm afraid.

The other avenue you might look at is one of the LiFePO4 batteries off ebay (Ping has a good reputation here), again linked via schottkies. This might be a better long term investment as theoretically at least the LiFePO4s should last much longer (in terms of years of use rather than range) than the NiMHs.

Look up an old thread by Tiberius called something like "modified torq has no problem with hills" or something like that, for more info on putting batteries in parallel.

Cheers

Steve

 

[mart.hart]

Give you some idea of the battery power I need !!

 

[flecc]

I would counter Flecc's claim that home-made extra batteries do not add much range, as my personal experiences have been good. My 12Ah home-made pack certianly outlasts my 10Ah original pack.

Quote from my post:

from small and cheaper rechargeable NiMh cells like AA or C size ones, coupling it in parallel via Schottky diodes to prevent cross transfer and destruction, but these don't extend the range very much

Somewhat different.
.

 

[flecc]

Much depends on how much a new battery is for your bike Mart, and since it's substantially cheaper than the Wisper, the battery is probably a lot cheaper too.

When assessing whether a large additional battery is worth making up, there's the cost of the 30 NiMh cells depending on the quality, small amounts for the diodes and thermistor, casing etc, and the major item of a 36 volt NiMh charger. Cheapest at the moment is probably the Powerstream one from the USA at £65 using a low cost postal service.
.

 

[mart.hart]

OK thanks.

The battery charger does take it up a bit and there is also a time issue as we go away in a couple of weeks.

A new battery is £300 so thats out.
The lipo4 on ebay are cheaper than that.

Thought of maybe getting one of them and then when my battery pack give up can maybe put them in the original battery case.

anyone know if there is import duty and VAT on them.

Mart

 

[flecc]

LiFePO4 cells are a bit heavier and larger than the usual Li-ion cells for a given capacity, so it may not be possible to us the existing case.

I understand that some importing the Li Ping batteries have paid duties etc bringing the price up substantially, so you could still get rather close to that £300 which is on the low side for a 36 volt 10Ah Li-ion at present. Current eZee price £395 for 10 Ah, Wisper price £514 for 14 Ah.

Hopefully someone who has gone the LiFePO4 route will post their costs.
.

 

[Beeping-Sleauty]

Li Ping LiFePo4 batts

LiFePO4 cells are a bit heavier and larger than the usual Li-ion cells for a given capacity, so it may not be possible to us the existing case.

I understand that some importing the Li Ping batteries have paid duties etc bringing the price up substantially, so you could still get rather close to that £300 which is on the low side for a 36 volt 10Ah Li-ion at present. Current eZee price £395 for 10 Ah, Wisper price £514 for 14 Ah.

Hopefully someone who has gone the LiFePO4 route will post their costs.
.

Thank-you Mr Flecc, one of Li Pings' 36v 10ah LIFePo4 including BMS & charger delivered to my door for £160 via EMS just over a year ago, the package did not attract any duty/import tax, and yes, i'm still delighted with it, we discussed these awhile ago:

http://www.pedelecs.co.uk/forum/electric-bicycles/1741-dilemma-replacing-my-sla-batteries.html

the prices have changed, due to the cheaper pound and are around £230, at the moment postage is free:

36V 10AH LiFePO4 Electric Scooter E Bike !Ping Battery! on eBay, also Parts Accessories, Scooters, Outdoor Sports, Sporting Goods (end time 10-May-09 11:47:46 BST)


... of course you cannot assume that Duty will not be charged and should factor this into the total (around £42)

 

[flecc]

Yes, this uncertainty on duties is a problem. Some have been caught with later charges, but I understand Jeremy was also lucky in escaping them, his pack for his recumbent coming to about £160.

As you say though Beeps, it's £230 now and could be £272 if caught by duty, both almost the same as the £300 cost of the new battery for Mart's bike. He has mailed me since to say that LiFePO4 is not an option because of the price.
.

 

[mart.hart]

Thanks everyone for your help.
Obviously no easy or cheap options here especially for occasional use.
If I towed everyday I guess £300 would be money well spent.

My biggest fear is a flat battery with the trailer on. It has 3 warning lights on the twist grip but they are totally useless

 

[flecc]

These charge level indicator light are never reliable Mart. They work by measuring the battery voltage and recording it's fall as it discharges.

Firstly that isn't an accurate method, and secondly, when the throttle is opened, the drain into the motor also shows as a drop in level. The only time the reading has any reliability is when the throttle is completely closed and the motor is not operating.

Fundamentally there is no way the charge content of these batteries can be instantaneously measured, simply because they are chemical devices, not electrical, the charge stored as a chemical state which cannot be accurately measured electrically.
.

 

[Alex728]

Thanks everyone for your help.
Obviously no easy or cheap options here especially for occasional use.

Thinking laterally, is there no way (after speaking to the vet of course) of putting the dog on a diet?

This assumes that by "fat" the animal is considerably overweight and it would make a difference in doing so - I expect if its just slightly overweight for its breed that may not do as well.

otherwise I suppose the only other option is to limit your journey, maybe vary the route instead so you and the dog see different scenery each time...

 

[Patrick]

How about changing your gearing with something like this

Shimano 11-34 Mega-Range 7 Speed Freewheel • Shop • Alpine Bikes

so that you've got an extra low gear to get you back if the battery does run out?

 

[flecc]

Another possible chance now for you Mart. Beeping-Sleauty who posted above has an old NiMh cellpack which hasn't been charged for a year but may be recoverable by repeatedly conditioning it. I've got a suitable charger and can try that conditioning, so he's kindly forwarding it to me in the hope that it will be ok for you. I'll let you know the outcome once I've received it.

Say thanks to Beeps.
.

 

[mart.hart]

Dog on a diet !!!
He’s big boned. Poor thing doesn’t get much exercise these days and can only manage about 100 yards.
So he’s not that bad just a big dog at 37kg
I could also lose a stone or three.

So there is a dog at 37kg me at 14 stone and a trailer so we really are pushing the boundaries of electric power here.

Rout planning is also a problem as last time we did an old rail track and went from Scalby (Scarborough) to Ravenscar and coming back the battery made it to Cloughton.
Also I didn’t do a whole lot of peddling as I had to keep waiting for the wife just going steadily so all in the bike did an amazing job and would cope wonderfully with normal use.

I must get a mile counter though, can you still get those little mechanical ones. I hate the digital speedo things that also tell you the time in 12 different zones.

Thanks again.

Mart

 

[Beeping-Sleauty]

.....I must get a mile counter though, can you still get those little mechanical ones. I hate the digital speedo things that also tell you the time in 12 different zones.

Thanks again.

Mart

.... Hi Mart, you may be in luck again today, i have one of those mechanical meters, about half the size of a matchbox, it is boxed & complete, almost as good as new, only 340 kms , ...but there's the rub, it is a kilometer counter as opposed to a mileometer, but it's free & yours if you want it...?

best regards,
beeps

 

[Alex728]

Dog on a diet !!!
He’s big boned. Poor thing doesn’t get much exercise these days and can only manage about 100 yards.
So he’s not that bad just a big dog at 37kg

Yep just within weight for a labradoodle / golden retriever cross or similar size breed...

hopefully you can get the extra battery for a few more miles. I use Memory Map for route planning but you may prefer a proper OS map to go with the mechanical mileage counter (where on earth did Beeping-Sleauty get one of these in 2009? I vaguely remember them when I first learned to ride bikes as a small boy in the 1970s...)