Lidl NiMH batteries

[Grizzly Bear]

Hi everyone
I've noticed that Lidl are selling very cheap NiMH batteries, and I decided to have a bit of an experiment, I wanted to see if they were up to being used as a backup/"get me home" battery pack. The only ones worth considering are the AA cells at 2500mah, as the C and D cells are low capacity, 4000 and 4500mah respectively. I assembled 32 cells, a multiple of 4 cells for £1.99, this equates to under £16 for a 2500amh battery pack. I have just tried them out, and found them to be well up to the job. The tiny battery pack took me up three considerable hills before giving up. For my use these would do as my main battery, as I only have these three hills to climb from my place of work. I think these batteries are well worth considering for anyone handy with the old soldering iron, be warned though, they do get a bit hot when charged with a 2amp charger.

Griz

 

[flecc]

That's what I found with the same capacity AA cells Griz, getting hot under charge, and also getting very hot when used on a high power (576 watt) eZee motor. They'd be better with a lower powered motor like the Powacycle.

With that high power motor the single bank of 32 cells wouldn't perform well, but two banks of 32 in parallel were ok for up to about four miles with two fairly steep hills.

For me it's a reserve "get me home" lightweight battery though.
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[Grizzly Bear]

Hi Flecc
they didn't get too hot under discharge in my use, for £16 for 38.4 volts 2500mah, I think they are a bargain, and as I said they could serve as my main battery. Using them in parallel as you suggest, to make a 10000mah battery, would cost £64, and be very light in weight too, D cells would cost in the region of £200. Durability is the only question, only time of course will tell.

Griz

 

[flecc]

Yes, they're certainly cheap, and for any given capacity, much lighter than D cells too. My full 10 Ah one weighed only the same as a Li-ion, around 20% lighter than D cells.
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[Grizzly Bear]

Following in your footsteps again Flecc. I have sorted my charger problems by the way, thanks for the good advice.

Regards Griz

 

[silversurfer]

Hi Griz, I too bought 32 Lidel cells but I went for the higher capacity 'D' cells. 4500mah does equate to 4.5 ah does it not? which seems to be almost half a small / medium battery pack. I wonder why you choose the smaller cell, is it just to keep weight down? I was concerned that the current draw on these tiny AA's would pull too much out of the batteries but, you test is very heartning.
I will be using them in a 36v li-pol powered torq as a get me home battery, hopefully with another 3 or 4 miles of range. I have done another post on this subject but I have lost my way on the many slightly differently titled forums. I will be building my battery in November as i will be away from 03 to 23 Oct.
Silversurfer.

 

[Grizzly Bear]

Hi Silversurfer
in regards to higher capacity, I meant the power to weight ratio of the cells, I do not want to add too much weight to my relatively light machine. I am not sure of how much heavier the D cells are compared to the AA cells, but at a guess I'd say that D cells are at least three times the weight of AA cells. They are of course much bigger as well, the 32 cell pack I've assembled is approx. 50x50x100mm in a configuration of 4 x 8 cells. As I mentioned, this is an experiment, and my thread was a report on my first use of this battery pack. The pack lasted about one mile of continuous moderate hill climbing, I do not use assistance on level ground unless there is a considerable headwind, so it's hill climbing ability I'm concerned with. I was expecting melt down of the battery pack, but that didn't happen, I am going to use this pack as my main battery to see how it holds up. I am off to Lidl straight after work today to buy up all the AA cells they have left, at £1.99 for four you can't go too far wrong.

All the best Griz

 

[flecc]

I am not sure of how much heavier the D cells are compared to the AA cells, but at a guess I'd say that D cells are at least three times the weight of AA cells.

The standard 9 Ah eZee 30 x D cell 36 volt NiMh battery weighs 5.5 kilos.

My experimental 4 x 32 (128) AA cells battery with 10 Ah weighed just under 4.5 kilos, so almost a kilo lighter. The AA take up a little less volume too.

If only the AA cells could deliver at the same current rate as the best D cells, everything would be perfect, but sadly they can't. It seems no-one manufactures moderate price ones for such a high sustained discharge rate.
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[Grizzly Bear]

Hi Everyone
Just an update on my Lidl battery pack experiment, I now have a 136 AA cell backup battery, 40.8 nominal voltage, yes I've over-volted it even further. This has progressed from 32, 64, and 128 cells, I can report that as yet I have had no dud cells. I have not tried my new 136 cell battery yet, other than running it with the wheel off the ground using the brake to load it, but I found the 128 cells to be more powerful than the main battery. I now have a new problem to be overcome, which is finding an electrical enclosure 250 x 125 x 60mm any advice on sourcing a suitable item would be greatly appreciated.

Griz

 

[Ian]

Glad to hear you're putting the soldering iron to good use Griz. Boxes similar to that size are available from RS components, but they're not cheap at £30+. Electrical wholesalers will sell a wide range range of suitable boxes, but again one that size will be expensive. Maplins have a good range of cheaper boxes but nothing that big, could you split your pack and mount it in 2 boxes.

 

[Grizzly Bear]

Hi Ian
I've looked at all the normal sources, but I've found nothing suitable as yet. I can report that my soldering iron is still performing in a mighty fashion, the tip is getting a bit eroded however, and I've filed it to suit soldering batteries.
How far do you think I can push the over-volting before I run into trouble?

Regards Griz

 

[Ian]

How far do you think I can push the over-volting before I run into trouble?

How long is a piece of string

I'd check the price of a new controller before you go much further since that's the most likely thing to suffer.

 

[Baboonking]

How far do you think I can push the over-volting before I run into trouble?

check the ratings of the main components in the controller, it will give you some idea.. Don't exceed the the capacitor ratings by more than a few volts. Run the bike with the controller exposed indoors and check for anything heating up or behaving oddly. For example I've found the powabyke controller to run fine at 48 volts (36 is standard) but it pwm chip does get hot and doesn't completly cut out when I realise the throttle.

Nice work on the battery pack. Bad idea to charge nimh in parallel but discharging is ok and as you've discovered, can give good performance.

 

[allotmenteer]

I'm running my 24V controller with a 36V Nimh battery (41V fully charged). It runs fine though it gets warm so to aid heat dissipation I have just strapped it to the frame so it's not waterproof.

Before over-volting I opened the controller and checked all the writing on the capacitors and mosfets and anything else I could see. The caps were 50V and the mosfets 60V rated so I took a chance and I haven't looked back. I've now got great performance, around 22-24mph on the flat!

Your bike is already running 36V on a tongxin motor isn't it? I don't think the motor will handle much more than this. Check out solarbbq's comments on this thread:

Endless-sphere.com :: View topic - The Tongxin Motor thread

Paul

 

[frank9755]

Hi Grizz,

Very interesting. One question; how are you charging your battery? Do you need to take it to bits and do the cells individually, or can you do it whole? If so, what charger do you use?

Frank

 

[aaannndddyyy]

I have been looking at making a AA battery pack for a while know after reading Flecc post aabattery I recently managed to get 340 AA NiCad rechargeable batteries off eBay for a penny each they come in packs of 5 spot welded together with a thermister fitted as you can see in pic

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They are only 700 milliamps so to make a pack for my Heinzmann 36v 5amp system, I would need 6s 8p setup which = 36v 5.6amp pack, I am not shore how I could charge them the easiest way would be to charge all in parallel keeping an eye on temp and voltage not going over 42v,I have read that charging Batteries packs in parallel is not a good idea but seeing that these packs have thermister in them so cut off would happen before over heating or explosion was possible and they were so cheap to buy I am tempted to try it, battery chemistry is new to me and the thought of blowing something up or causing thermal runaway worries me a little (NiCad are bad for the environment), as long as I make shore that all packs are close to the same voltage and I don’t drop the charge say below 36.1v on discharge maybe that could work, or am I playing with fire?. Otherwise Shottky barrier diodes would need to be used and charge the batteries as 36v 700 milliamps, but charging 8 individual packs would take to long, unless I can find say 4 chargers then I could charge the packs up in a quarter of the time but the price starts to go up.

 

[flecc]

I think it's best to just go the cheap way and charge in parallel Andy, best not to spend too much at the outset. Just rely on monitoring temperature by feel and keeping the charge moderate, since if successful, you could improve things later.
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[aaannndddyyy]

NiCad is slightly different from NiMh. Nickel Metal Hydride (NiMH) batteries offer high capacity (over twice the amount of Nickel Cadmium (NiCd) batteries), quick charging capabilities and great reliability. With a relatively low internal resistance,
NiCd cells work well when fully charged, then fully discharged at full power, then fully charged, and so forth. They work less well if a device is continously recharged in between brief, low-power uses. With a relatively low internal resistance, a NiCd battery can supply high surge currents Nickel Cadmium (NiCd) batteries have a longer cycle life, though shorter run-time than NiMH batteries. They are the most cost effective rechargeable batteries and can last up to 1000 charges. They are hardy and can withstand very low temperatures and rough use. Like all rechargeable batteries, NiCd batteries need to be completely charged before their first use.
I have already striped and pulled apart a few of these packs as they have button ends and have used them in my bike lights and remote controls ect, they have all worked fine so far

 

[flecc]

Thanks Andy, my mistake, I'd missed they were NiCad and not NiMh, so am amending the above post.
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[Grizzly Bear]

Thanks for the advice, I think I will back off on the voltage, it runs fine on 32 cells, and I want to keep reliability. I have found charging in parallel to be ok, my charger cuts out at about 46 volts with a 128 cell pack, it went to 49 volts with the 136 cell pack, it is called a High Power model HP8208N3, it did have a discharge facility, but that burned out last night whilst discharging the 136 cell pack.

I had a bit of an accident with the battery last night, which resulted in many short circuits, two cells are dead as a result, one of them was venting flame. As Flecc has previously reported, the solder acts like a fuse, who said AA cells can't provide sufficient amps? These were supplying many!

I think I've found a supplier of an enclosure, the lack of which caused the accident, wrapping with insulating tape was ok fo 32 and 64 cells, but 136 was just too much.

Griz