Yamaha XPC26 battery recell

[Pedunculate]

I have a 2000-vintage Yamaha XPC26 that is probably up for a recell soon. It's been barely used, stored in the garage and until I got it probably done less than 50 miles from new. It's the lead acid version - the battery (24V, think it's 96Wh) is surprisingly good after all that time - I get about 10 miles out of it on a good day. However it's being a bit erratic, deciding to cut power after only a few miles (switching off and on again cures that), or claiming that I'm on low battery about a mile off a fresh charge. I've done 'refresh charge' a few times, but that seems to make it worse. The 10 mile range is a bit annoying as it sometimes isn't enough for a round trip.

Anyway, I've been looking at recell options. I haven't actually got the case apart yet (hidden plastic clips) as I've been using it a lot, but I assume some appropriately-sized SLAs would be easy to obtain. So it looks like my options are a straight SLA swap, or change to NiMH.

I can get 20x 9000mAh D-size NiMHs from a non-eBay retailer for £85, which would make a 216Wh battery (tagless, so I'll have to solder them into a pack). I presume I'll need a new charger (NiMH charging not being rocket science, this shouldn't be too expensive). I'll have to check the NiMHs are rated for high discharge current.

One question: the bike has its onboard charge gauge. This is what's causing some problems with the power cutting out when the bike incorrectly thinks the battery is flat. If I recell with NiMH, will the change in battery discharge curves cause trouble with the charge metering? I imagine it's stored on the microcontroller somewhere, so not easy to change. The bike also comes in a NiCd version, so unless there's a handy SLA/NiCd jumper somewhere?

Any other tips for doing a recell? I have a 150W soldering 'gun', so the plan is to make up packs by direct soldering to NiMH cells (soldering fast with lots of flux).

Cheers!

 

[oigoi]

The change to Nimh cells will mess up the charge metering, as the voltage of the battery when it is fully charged will be different.

They might have used the same charger for the nicd version with some tweaks, you might need to pull it apart and do some investigating. It is equally likely they would us a different circuit board for the nicd version.

I did build a 24v pack once with the type of nimh cells you are talking of, but I split the pack into two 12v packs for charging and charged it with a car battery charger but I had to manually monitor the voltage of the pack when it was charging and switch off the charger manually.
You would be better off buying tagged cells as the cells may not like the heat of a 150w soldering gun being applied to the ends of them.

Hope this helps

 

[flecc]

I'd be inclined to stick to the SLAs since they've served you so well. With D cell NiMh so out of fashion the quality of most of them isn't very good and it's advisable to overbuy a little to get a good matching set.

NiMh charging on e-bikes is actually a bit more sophisticated than lithium charging, the latter cared for by the battery's BMS. For good NiMh cell life it's best to have an NTC thermistor incorporated in the pack matched to the charger's cut-off circuit value, giving thermal cut-off rather than the inaccurate voltage cut-off. Typically the NTC thermistors for most good chargers have values of B: 3500 to 3950 and R: about 10k.

 

[Pedunculate]

Thanks for the advice. I finally got around to cracking the lid on the battery (4 big self-tapping screws plus a single long plastic clip in the middle on each side of the battery: a few old credit cards got me in eventually). And the news is... it contains 20 NiMH D cells!

Which is a right turnup for the books, since Yamaha only sold SLA and NiCd versions of this bike and this one was bought as new as SLA. I didn't think there were NiMH powered e-bikes available in 2000-2 when this was bought as new/old stock from a Yamaha dealer. The battery charger only says 'Yamaha battery charger' on the outside - makes no mention of chemistry, so I suppose it's a NiMH charger after all.

The 9Ah NiMH D cells I was looking at were 'consumer' GP900DHCs from buyabattery.co.uk at £8.50 for 2 (datasheet). The bad news is that these are only rated for C/10 charging at 900mAh, and the max discharge current is 27A. The GP900DH (datasheet) which I confused them with has fast charge of up to 4.5A when using termination control (think there's a thermistor in the pack, though there's also a 2A car spade fuse on the charge connector) and discharge current rated up to 45A.

The cells themselves in the pack are unmarked, so I have no idea what kind of rating they actually are. The charger is 24V 2A. Would I be hugely abusing the consumer cells by charging them at 2A (so 0.22C)? And then what kind of current drain does an e-bike take? Is 27A (so 650W peak, at cell voltage 1.2V, or 540W when flat at 1.0V) sufficient? I've also regeared the bike by putting a smaller chainwheel on the rear hub, which probably increases the load. I suppose I ought to buy one of the R/C battery charge monitor gadgets and put it in series to find out.

Anyone suggest another source of NiMHs at sensible prices?

ETA: I've just discovered that the connector between the battery and the bike comes apart, and contains two car-style spade connectors. One is a single pole with a thin black wire, not sure what it is (voltage sense perhaps?). The other is a dual-pole with thick black and red wires, with a spade fuse mounted in the middle of the connector. It's a 30A spade fuse. So that presumably answers my question about the max discharge current: I think 27A will be sufficient.

ETA2: I've dug out the brochure, which says:
Battery: Yamaha 24V/5Ah NiCad
Battery charger: Automatic quick charge
Battery charge time: 3.5h
Motor: 235W
Range: 25 miles
Range in economy mode: 37 miles

The brochure doesn't necessarily correspond to the bike as-bought, of course. But that suggests a charge rate (allowing 20% extra charge time due to inefficiency) of (5x1.2/3.5)=1.7A. So that would be 0.19C. While this is twice the specced charge current, is it likely to be a problem? I would feel not, but I'm not sure.

And a 235W motor doesn't say what the peak current is - only 2x doesn't leave much of a margin. The fuse isn't going to notice the peak current, which could be higher than it is rated.

I'm feeling like the 'consumer' batteries are worth a go. Anyone have any opinions?

 

[flecc]

The 27 Amp discharge current is plenty, more than most e-bikes need so no problems there. The thin black wire is the thermistor connection to the charger. The other side of the thermistor within the battery goes to common earth, the charger's thermistor resistance circuit being typically loaded with about 5 volts.

Both charging and discharging use the thick red and black wires.

 

[Pedunculate]

This bike is unusual as the battery has separate charge and discharge connectors. The discharging connector is at the bottom of the battery and has (in order) thick red (+ve current), thick black (-ve current) and thin black (?). The charger connector is a different type at the handle end of the battery and has (in order) thinner red, thin 2-core fig8 black and thinner green (thinner=thinner than the discharge wires). Presumably the thermistor is on the 2-core fig 8, and the other two are 2A charging inputs (thinner red has the 2A spade fuse in series). I'm guessing that the single-core black on the discharge connector is a voltage sense line for the handlebar power meter, so it isn't confused by voltage drops in the current-carrying conductors. Though I'd have expected a 4-terminal measurement, not a 3-terminal one (after all, there will be just as much voltage drop in the ground wire as in the positive wire)

I'll see if I can put some pictures up somewhere in case anyone else is interested (I didn't find much info about the XPC26 out there)

On the subject of 'overbuying' cells, how many extra cells would you recommend buying? And how to work out which ones match? I'd need to overbuy anyway to perfect my soldering technique (unless someone can point me in the way of a supplier of tagged cells).

 

[oigoi]

RS sell these:

RS | Batteries | Rechargeable Batteries | D Rechargeable Batteries | NiMH Rechargeable Industrial Tagged Batteries

which is a 10000mah (10ah) tagged d cell

 

[Pedunculate]

Hmm, at 4x the price (£8.50 for 2 against £13.65+VAT=£16.38 for 1). And they don't give any technical data. Think I'll pass

I'm also plotting... I'm wondering whether I can make a little board to fit inside the battery to do charge monitoring. This thread has some ideas. There's a small amount of space available (about half a D-cell's worth) - it'll be tight but the charge monitoring chips are small. Ideally I'd like a USB port on the battery so I can download the performance

 

[flecc]

I think you've got those connections right. Those bikes with separate charge inputs and NiMh batteries just have the charge and load connections common internally. Having both thermistor wires into the charger is quite a rare configuration, but the circuit could still be earth terminated within the charger.

 

[Pedunculate]

I looked into making a spot welder like this one... I have a 68000uF 35V capacitor so I might try it sometime, if I can work out a cheap way to make a 35V power supply (which would get me about 30% of the joules of the above design).

I've also had a play with soldering up some dead alkalines to tin/brass-plated strips cut from the lid of a baked bean tin (no expense spared here!). I've got a good mechanical strength, to the extent that they took several blows with a hammer (denting the battery) before I got them off again. My technique is:

1. Make sure your soldering iron is really hot. I'm not sure my gun is working 100% as it takes some time to come up to temperature (odd, when it has 150W to play with). I kept the trigger down for the whole of this procedure.
2. Dip the end of the metal strip in flux (coat both sides)
3. Put a blob of solder on the end of the gun (about 4-5mm in size)
4. Bring it onto the metal strip, wait for the flux to boil away and a tinned surface to form
5. Repeat to tin the other side of the strip
6. Now dip the end of the battery in flux
7. Put another blob of solder on the end of the gun
8. Bring the gun down onto the end of the battery, wait for the flux to start to boil and the end of the battery to be tinned. Leave the solder blob there. About a second.
9. A fresh blob of solder on the end of the gun (these blobs ensure good thermal contact, which is vital)
10. Bring the soldering gun down on the top side of the metal strip, wait for the topside solder to melt (which indicates the bottomside is melting too), keep the gun there.
11. Bring the gun and tinned strip down on top of the blob of solder on the end of the battery. Wait 1 second. Remove gun
12. Hold steady and wait for it to cool (2-3 seconds)

I have some cheap'n'nasty new zinc chloride Ds and 800mAh AA NiMHs to test later and check I'm not damaging anything. I also tried abusing alkaline batteries: I didn't get anywhere with overheating them, but after a fair bit of hammering I managed to piece one and at the same time short it, causing it to get warm and acid to leak. So I think it's hard to overcook alkalines.

Now, another question: is there somewhere to get the metal strips to link cells? I asked at my local metal supply place and the best they could do is 0.6mm copper sheet, which is a bit thick. I see some Hong Kong suppliers have precut tabs on eBay, but they're either too short or too narrow for me. Is nickel the best metal for this? I don't really want to eat that many beans ;-)

 

[flecc]

I've used strips cut from old tin cans in the past and they've worked ok. I've never had a cell failure after soldering and I usually pre-tin and then use as high a heat as possible for the shortest possible time to join.

 

[Pedunculate]

I suppose I could take tin cans and hammer them flat... time to get eating those beans!

(I do enjoy wandering around supermarkets looking for items for the packaging not the contents... currently the cheapest glass bottle in Sainsbury's is 22p... anyone want a dozen litres of Economy Brown Sauce? Actually, I could probably use it as bathroom limescale remover...)

 

[banbury frank]

Hi
Found these on Ebay


This company supply tagged battery's not cheap £9 each but made for the job can make pack for you They offer a refurbish service

CPS Batteries items - Get great deals on Custom Orders items on eBay.co.uk Shops!

Yuasa 1.2 V 9000 mAh D Ni-MH Industrial Flat Top Cell | eBay UK



Frank

 

[Pike Rob]

Hi
I have been lucky enough to pick up 2 2002 MBK Ax-ion citys French badged Yamaha XP26 , they are excellent for what I wanted as the hills here are very steep and the MBK deals with them at ease , and are fun to ride but as usual one battery is dead and the other dying , although I have used the bike using two fully charged but they aint taking me far because they are losing charge rapidly , I`ve seen threads here about putting in non standard cells , here in France it is possible to buy of the peg Ni-CD new replacements for €185 including TVA and free postage and there is a battery specialist that claim to refurbish them . Any advice welcome
Regards Rob

 

[flecc]

The off-the-peg replacements seem to be by far the best option Rob, since that price is very competitive for an e-bike battery these days. The standard of most replacement NiMh large capacity D cells these days is very poor, there being no manufacturing demand for them to ensure the quality we always used to get.

 

[neptune]

I am surprised that you can still buy NiCad battery packs off the peg. I was under the impression that the manufacture of these had now been banned. I have noticed that there are still plenty of NiCad power tool batteries for sale on Ebay, but I wonder if these are old stock?

 

[flecc]

I am surprised that you can still buy NiCad battery packs off the peg. I was under the impression that the manufacture of these had now been banned. I have noticed that there are still plenty of NiCad power tool batteries for sale on Ebay, but I wonder if these are old stock?

Under the so-called "batteries directive" (2006/66/EC), the sale of consumer Ni–Cd batteries has been banned within the European Union except for medical use; alarm systems; emergency lighting; and portable power tools. I think that probably leaves a loophole for others to obtain cells to make up packs for other uses, especially as there is no ban for industrial use.
.

 

[smudger1956]

I am surprised that you can still buy NiCad battery packs off the peg. I was under the impression that the manufacture of these had now been banned. I have noticed that there are still plenty of NiCad power tool batteries for sale on Ebay, but I wonder if these are old stock?

Yes, so was I, I was informed that NiCad production world wide had ceased, I also did hear that NiCads were still being produced in Mexico.
Shame NiCads are made from such environmentally unfriendly materials, and did not have a higher AH rating.
I particularly fond of Sanyo SCR cells, especially matched packs for my RC models.

 

[neptune]

That being the case then ,how feasible is it to make bike batteries from power tool batteries. Unless I am wrong, the big advantage would be long life . Is there still acase for NiCads?

 

[flecc]

I like NiCads for the way they can freely give up their content, not impeding motor power in any way. On the downside is that they don't like part usage and charging, suffering memory effect that loses substantial capacity. On an e-bike that ideally means riding with two packs, using one completely first and then swapping over.