A DIY back up battery.

[silversurfer]

Hi folks, I think, well I hope I have come into the correct forum following the sticky thing!
I recently bought an S/H torq to get fit after some heart repairs I had a few years ago. The torq gives me about 20+ miles range on mixed pedal/motor use, however I do not want to get stuck on some of the hills I encounter, (usually on the way back!) so I have been contemplating a back up battery.
Having a fair bit of experience with motor vehicle electrics I reckon I need about 36 volts and a few (probably up to about 10) amps. Ni Hi batteries seem to fit the bill. As luck would have it at the time of my thoughts, the Aldi supermarket was running a promotion on Ni Hi cells, the D cell 3.5 amp variety.
After visiting two stores I managed to get 20 cells at £1.25 per cell. A 2 mt length of 40 mm grey plastic water pipe, cut into 3 pieces approx. 62 cm. accommodate each set of 10 cells quite nicely. Suitable end capping pieces are available to enable contact and pressure to clamp the cells tightly.
I have assembled one such pack; it’s a 'tube' 65 cm long and weighs 1.25 kg.
And now Liddel supermarket are running a promotion on Monday 10 th Sept.for D cells, 4.5 amps at £1.00 each, so I can get the last 10 cells!
(But I am not sure how 3.5 and 4.5 amp cells mix?)
Anyway, I am sure I can fabricate the cables and push on sockets to pick up on the power input pins and clamp the tubes together to fit on the carrier.
However I need some advice.
10 cells give a 12 volt nominal EMF (36volts for the three 'tubes') but, will the motor demand pull the voltage down to below the cut out level in the controller? If this is likely, would adding an extra cell per tube compensate for the voltage drop? Would this higher voltage (40 volts) upset the controller?
Charging; If I can pick up a 36 volt charger ( I'm sure my Li Pol one will not be suitable) will it kick out enough to service a 40 volt pack (if not I will have to do them in 4 cell batches on my little domestic ni cad charger) ?

At Liddel prices it could mean a 30 cell 4.5 amp battery could cost £30.00 plus about £8.00 to £10.00 for the plastic bits.....cheap enough, if it has the grunt to deliver 5 to 10 amps?
As an aside, would these cells be suitable to re-cell an existing battery case? Again, for use as a back up/get you home pack.
Over to you electronic experts !!! Ted

 

[flecc]

Highly dangerous Ted.

One of the problems with NiMh batteries is cell matching, and battery manufacturers insist on cells for their packs all coming from one manufacturing batch to ensure identicality.

Mixing those two batches is highly likely to cause a burnout of one or more cells of one type or the other. This can cause a plastic case to melt due to the very high temperatures generated and even cause a fire.

I've had success in adding three cells of known high quality to an existing used battery by using careful charge matching and gradual running in. However, a similar attempt with one cell of a different type added to another battery resulted in an immediate burnout.

All in all, making up these packs is potentially very risky, and should only be attempted using batches from one production of a known and respected type. That almost never includes bargain prices, the successful ones usually costing around £10 per cell in the UK. It's almost always much cheaper and easier to buy a ready made battery like the eZee 30 cell one at £190.

These cell matching problems are I'm sure the reason why manufacturers are so insistent on adopting Li-ion types, despite customer resistance.
.

 

[Ian]

Hi Silversurfer,

Those cells sound a bargain. 30 is the correct quantity, being the number used in the Ezee NiMh battery, although those are 9Ah capacity.
There is a potential problem in mixing cells of differing capacities as the lowest will become exhausted while the higher capacity cells are still delivering full voltage. When this happens current from the charged cells will flow through the discharged cells in reverse, permanently damaging them. To avoid this it would be necessary to stop as soon as a voltage reduction was noticed.

The Li charger you have would not be ideal as its output voltage is lower than that of a proper NiMh charger, an additional complication is the that proper NiMh chargers monitor the battery temperature with a thermistor embedded in the pack which is specific to the charger. Any 36V NiMh charger could be used if the charging was done on a time only basis, eg 2hrs @ 2A from flat.

While there are difficulties, they are not insurmountable and providing that you fully understand those difficulties I would be inclined to buy the cells and then think about the problems.

PS. Just seen Fleccs post. He is correct to point out the potential dangers which should be fully understood before attempting to make or modify any battery pack.

 

[silversurfer]

DIY battery

Thanks for your prompt reply, on the face of it seems like I have an insurmountable, potentially dangerous balancing act. I'm glad I made this post before buying more cells!
The workings of Ni cad/Ni hi are a dark secret to many (inc. me!). Your reply has also now addressed why the Ni cad cell packs used on other kit I have (battery drills, camcorders etc) have failed, when, upon opening the packs there is just one cell down. I have on occasions got things working by swapping similar sized/rated cells but invariably it was short lived, the pack died when another cell went down.
To get back to the thread, it seems I now have a 24 volt '2 tube' pack ' to sell/ break up/or use for some other 24 volt project! I have an old Velo Solex French cycle motor with a sized engine, I have toyed with the idea of driving it with a redundant 24 volt mini bike motor, but that will be another thread, if I ever do it!
Realistically it is not worth buying another 30 cells, (plus I must buy a 36 volt charger) then make the packs, in order to gain another 5 or 6 miles of range! I'll just have to get off and walk up the hills.
Still puzzled about the potential volt drop on load of relatively small amp/hr Ni HI or sealed lead acid cells, (I am much happier with simple, cheap lead acid batteries) will the controller just cut out when the pack voltage gets pulled too far down when the load is applied? I ask because my fall back idea is to use three 12v. 7 a/h SLAs, they weigh 2.2kg each, can be charged with a normal 12v charger and are quite cheap. BUT, if the controller gets upset and cuts out that will be another £40.00 or so lost, and the 'boss' will not be happy (even though I have just bought her a new washing machine)! thanks, look forward to your words of wisdom, Ted

 

[flecc]

When the voltage drops too far, the controller will indeed cut out Ted, but I've never known that happen on an NiMh Torq, since NiMh voltage drop is not normally extreme enough. It does happen on Li-ion batteries when under heavy load though, and the controller cut-out point is 32 volts.

I couldn't guarantee that SLAs wont drop to the equivalent 10.6 volts each under load, and I think an additional standard NiMh battery is the best bet. That's what I use for extra range, though I did experimentally produce an AA based 2.5 kilo half capacity backup battery. The problem with that is that internal resistances mean it only gives a quarter range from it's half capacity, and I think it's long term reliability will be suspect.
.

 

[silversurfer]

Thanks flecc, more or less as I suspected, A 'little' small ah. battery has less grunt to hold up under high loads (did'nt realise it could be 20amps) i can't imagine even D cells holding up for long, let alone AA's. I suppose the gradual creeping up of advertised ah. capacity, (I seem to remember the last Ni cad D's I bought 'trade' from Radio Spares were 1.2 ah.) may be a peak reading under light loads. I am mulling over the economics of another 30 or 33 cells... if I can dispose of the new 20 set of 3.5ah cells to someone with a 24v bike wanting a backup battery.
The problems with keeping a Li iron battery in good condition as a costly (£250.00) back up has forced me to consider doing it myself, or making sure my journey is less than 20 miles. Incidentaly my torq motor sounds like an old tram car when it takes up the load and whines/resonates as I travel, the previous owner reasured me this was typical of torq's so I carry on, but people do know when i am approaching! Oh, it's done 226 miles on the clock.
Ted.

 

[flecc]

The best makes of 8 to 10 Ah D cells are genuinely that under load Ted, and the range on the 9 Ah ones in the eZee bikes compared with that on the 10 Ah Li-ions does bear that out, it's very little different.

The Torq motor is noisy from standstill to about 12 mph, especially if full throttle is used, as this is the "wasteful" consumption band, where the energy used exceeds that required for the power generated, the surplus expended as vibrational and heat producing modes. This happens on all electric motors, just listen to a milk float going uphill at a low speed, but since the Torq motor is so high geared, that band is 50% longer than usual with e-bikes, and the noise generated at the beginning that much louder.

From about 12 mph upwards it should get markedly quieter as the revs rise. However, these do vary in respect of just how much quieter they get.
.

 

[silversurfer]

Thanks flecc, thats exactly how it is, as it gets faster it gets quieter, the spokes seem to add a varying 'harp-onic' sound, a cross beween a stuka and a grumpy cat! I have discoverd some interesting information on a French built electric bike, the 'Cybien'. I will try to scan the brochure or I could post it to you/the forum, quite an interesting bike. Ted

 

[flecc]

I'd be interested in that Ted, I've never heard of it.

I like the graphic sound description, I've never got further than "angry, whining growl".
.

 

[Haku]

Hmmm...

DeWALT DC9360 36 Volt, 2.4 AH, Lithium Ion Battery Pack

 

[Ian]

Hmmm...

DeWALT DC9360 36 Volt, 2.4 AH, Lithium Ion Battery Pack

I've been slightly tempted by these in the past but am concerned by unconfirmed rumors that the actual voltage is closer to 33V, useless on an Ezee bike with a low voltage cut off of 32V. There is also the question of how they'd stand up under sustained high load, the power tools will be designed to tolerate the effects of chemical exhaustion but a bike controller designed for a much larger battery will not have that tolerance, cutting out as soon as the voltage falls to 32V.
By the time a charger has been purchased the total cost begins to approach that of a spare battery which requires no adaptations and carries no uncertainties as to its suitability.

 

[Haku]

You're certainly right about the price thing, especially if you're going to buy more than one pack to hack apart, you've then got the added problems of charging and putting them into a case of some sort.

I posted it because I thought it interesting that at least one major company is now selling these types of lithium packs, which will probably mean others following suit and subsequent competition where prices will go down.

Originally found it from Hack a Day where they link how to strip down a DeWALT DC9360 pack and the KillaCycle which uses 990 of those A123 cells to achieve drag racing speeds up to 155mph in 8 seconds (0-60 in 1.04 seconds!) - you gotta see the YouTube video clips on that site.

 

[Ian]

The temping thing is that an ultra light low capacity get-you-home battery is just what I need. Perhaps I should buy a macho 36v DeWalt drill to justify it. Or a drag bike.

 

[ITSPETEINIT]

Suitability and Sustainability

I've been slightly tempted by these in the past but am concerned by unconfirmed rumors that the actual voltage is closer to 33V, useless on an Ezee bike with a low voltage cut off of 32V. There is also the question of how they'd stand up under sustained high load, the power tools will be designed to tolerate the effects of chemical exhaustion but a bike controller designed for a much larger battery will not have that tolerance, cutting out as soon as the voltage falls to 32V.
By the time a charger has been purchased the total cost begins to approach that of a spare battery which requires no adaptations and carries no uncertainties as to its suitability.

From where I am viewing this discussion, and my standpoint is certainly as complete novice (oops! nearly said 'idiot') on the technicalities referred to, it seems the discussion is 'turning in' on itself'.
These 'alternative' lower capacity, cheaper and DIY variants do not have the suitability of those purpose-made for the particular electric bicycle.
The answer to 'the standby battery' is a spare battery of the same size and type - Lithium or NiMH, depending on one's chosen type and its charger.
One must accept the inevitable degradation: more slowly if it is less discharged or even more slowly than that if it is seldom used.
Where the degradation is slower, then there comes a time when it is appropriate to switch them around, or one may take the view that (in the case of Lithium) that using them much less close to deep discharge (swap them over half way) will maintain their useful life that much longer. Given that the particular journey is regular (like commuting) the end result will be the same: both batteries will degrade at the same rate.

Which is what I do with THREE Lithiums - run them at 10 miles each on my touring sorties, or further if needs be. They are already, on my typical 'hilly' route, down to a maximum <20 miles to 'the Yellow LED is on permanently when riding on the level'. Two of them were purchased 'New' (one in May '07 and the other in June '07). A really new one gave 27 miles on it's first deep discharge and 24.5 miles on its second. Same journey exactly, on a Sprint 7 (no modifications). Perhaps the weather conditions were adverse on the second run, or I was in need of more 'rest'.
I must prepare a profile of that 21 mile route one day, so that I have ALL the statistical components for comment: Total weight of bike, luggage and rider, profile of route and weather conditions. Out and back should provide a reasonable average for comparative purposes.
Peter
PS. All this discussion arises (well, most of it anyway) because one's chosen model had a certain 'range' that fitted in with one's intended use/journeys, (say 20/25 miles), only to discover/learn that was the mileage to deep discharge which is to be avoided. The practical discharge level is probably 75% of that if severe long term damage to capacity is to be avoided and as little as 50% if the battery is to maintain its optimum longest life.

 

[Ian]

Your reasons for using multiple batteries Peter are rather different to mine. All my current batteries are NiMh so discharge to cut off does them no harm. I do on occasions carry a spare battery but the only times I've needed it were with only 3 or 4 miles left to do and a lightweight battery would be a lot easier to carry around "just in case" it's needed. I don't mind if it's not fully up to the job but it does need to work without constant low voltage cut outs so I'll let someone else do the testing.

 

[flecc]

Ian's is exactly the same as my circumstance, using NiMh but occasionally wanting 3 miles or so of spare capacity "just in case". The AA cell based battery half filling an eZee case and weighing 2.5 kilos does that for me now, but it performs at a lower level than the normal battery, and charging is more fiddly, since I have to cut it at an appropriate point.

A "C" cell based battery would be much better, but all the suitable cells are almost as expensive as full size D cells, and dearer than buying a new battery from 50cycles.
.

 

[silversurfer]

diy battery

Thanks guys for your valued comments,I am still mulling over the advice, I cannot really justify a second £250.00 battery that probably will not get enough use to justify its purchace,I am an irregular user, not a commuter or an energetic tourer like Pete! The Lidel offer starts tomorrow and the D cells were the first to go at the recent Aldi promotion, so i must decide 'to go or not to go' I will re-read the tips and flecc's AA battery article, SS

 

[flecc]

An email re: these on the way to you SilverSurfer.
.