Replacing SLAs with NiMHs

[Andy]

Hi there - I'm new!

I have this Sakura S200:

Andy Wade's 2004 Sakura S200

and I want to replace the 36 / 48v, 13amp SLA with 40 10 or 11 amp NiMH D-cells (and maybe a bank of AAs or another bank of D Cells to supplement that up to over 14 amp if neccesary - my calculations show that I need at least 10 amp though)

Am I right in imagining that this is actually possible? I'm hoping that I can get increased performance and range by losing the weight penalty of the lead-acids, and / or increasing the amps available.

It seems like a pretty simple bit of DIY, but when I talked to the dozy Sakura bloke on the phone he claimed that switching to the Sakura's own Lithium batteries would require a re-wiring job. I can imagine this being the case with Lithiums what with their tendency to blow up and all, but what about NiMHs? Surely if I've got the amps and don't overheat my battery pack I can do it?

BTW, I was going to use AAs but then I read a load of articles linked to on your forums which proved to my satisfaction that they're more trouble than they're worth, what with the internal resistance and overheating and stuff.
Thanks to the guys who did that and put it on the web - you've saved me a packet!

 

[flecc]

It's also very risky with D cells Andy.

Battery manufacturers take great care to use cells from a single manufacturing run, and the better battery manufacturers also match the cells before assembly. Technically cells in series should be charged via their own cell charging circuits or have voltage matching circuits interposed, and Lithiun batteries do have that now, but NiMh have always relied on the cells being close enough to each other to avoid disaster.

It's for these reasons that the best D cells cost around £10 each or more, and using the much cheaper sources that are around can end in expensive failure and a melted battery casing. I've even had the odd failure of the most expensive cells.

The other problem that's common with low price cells is inadequate discharge rate, and for your powerful motor that would mean greatly reduced performance and the battery getting hot. If the conditions aren't right, the battery life is greatly reduced and could be only a few months.

So yes it's possible, but perhaps only a 50% chance of success and full satisfaction on your bike, with reduced power quite likely. The higher capacity F cells might be better at avoiding reduced power and also getting around 13 Ah, but they are half as long again and expensive.
.

 

[Andy]

Oooh, thanks. That sounds bad, considering I'd been trying to improve performance... What do you think of these:

E-Bikes Kit & Batteries - 48V Battery pack

Alternatively: What about using 2.6 amp, 48v AA clusters to augment the main battery? Should give me more range, maybe another 4 miles or so I reckon. I could build a switch and use a plug-in thermometer to turn it off if it gets too hot, and blocking diodes to stop it sucking power out of the main battery. Has anyone tried this?

 

[allotmenteer]

Hello Andy

There have been quite a few quality issues with Batteryspace packs. One of the forum members got a pack from them that was just fine though. However their prices are very high still and you'd also get hit with high postage costs and plus whatever customs decides to add on.

A better bet would be to source them from the UK. You could always try 2 Nimh battery packs from powacycle. They are 24V 8Ah. The packs are £99 and the chargers £40 each. You'd have to charge each pack separately though.

You'd also need to find out whether they would fit in the space vacated by the SLAs.

Paul

 

[flecc]

Paul's solution with the Powacycle packs is a good one if 8 Ah is sufficient, but sadly they've now risen to £129 each.
.

 

[allotmenteer]

Paul's solution with the Powacycle packs is a good one if 8 Ah is sufficient, but sadly they've now risen to £129 each.
.

Crikey! I haven't checked the site for a couple of weeks. Perhaps they have been selling so many of them to be used in other kits / bikes that they've decided to make a bigger profit on them.

 

[Andy]

Hmmm, thanks guys, you've put me off the probably suicidal idea of spending tons of money on NiMHs to replace the SLAs.

But what about range extension? I might start a new thread soon...