Schachner thermistor?

[tourtoe]

Hi all - I have a 36V 11Ah DIY battery pack (matched cells) and a Schachner charger. I can read from several posts that the thermistor in the pack should match the charger - does anyone know which thermistor Schachner uses?

It's all supposed to make this monster go.

Cheers,
Torben

 

[flecc]

I don't know that one's value, but you can do as the manufacturers of generic chargers do and use a generic value to suit all types.

Typically a 10 kOhm one with a Beta factor of around 3950 will do the job.

Here's one that will do:

NTC thermistor: Radiospares part number RS 151-237. The characteristics are R = 10k, B = 3914. Mount it in close contact with an inner cell wall near the top of the battery pack.

But first, if there's one there, measure the resistance of the one that's in your battery. If it's between about 8 kOhms and 12 kOhms at room temperature, try using that first.

To check the charging characteristics with any thermistor, the battery should get quite warm at end of charge but not hand burning hot, and the voltage immediately after charging should not be over 45 volts absolute maximum, but not less than 39 volts.

I can't absolutely guarantee a generic value will work, but they do most of the time.
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[tourtoe]

Thanks a lot - I don't have an original pack, so no help there. The problem was this (there's news!) : the charger expected a thermistor/resistance and unconnected it only measured 5v between 2 pins, and 4,2V between 2 others.

Now I have a test going on with a 10Kohm ordinary resistor, and a temperature probe (from the kitchen ) in the battery. And it delivers ~39,3V 1,3A now, so I'm on the right track.

The Schachner charger has a XLR connector and it expects positive on terminal 1, common on terminal 3 and a (probably) 10K thermistor between terminal 2 and 3.

The local electronics shop only had a "no-spec" 10K thermistor (which measures 13Kohm at room temperature) so I'll certainly look into the RS option. I have also emailed schachner, but I don't hope too much for an answer.

Cheers,
Torben

 

[flecc]

In fact many chargers have an upper voltage cut off limit and with those the thermistor can be replaced with a 10k resistor for a while without harm.

That peak voltage you measured would be surprisingly low if measured without a load, but I guess you measured it while connected to the cellpack. It's normally about 50 to 54 volts quiescent on NiMh chargers as headroom is necessary to get a full charge.
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[tourtoe]

Yup, the 39,3V was with the batterypack at ~32V, now it charges at 42V.

Cheers,
Torben

 

[flecc]

That sounds perfect.
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[tourtoe]

I have also emailed schachner, but I don't hope too much for an answer.

I did them wrong - received this :

Dear Torben!

Thank you for your email!
The NTC-termistor has at 20°C approximately 10 kilo ohms.

We hope we could help you with this information. If not please do not hesitate to contact us!


Not too precise, but confirmation is a good thing

The charger changed to maintenence mode when the battery was at ~42.9V - the battery never got too hot, but I charged it in several steps - I didn't want to leave it for too long connected to the charger. But everything seems OK.

Tonight - with some luck - I'll test the ElFocus.

Cheers,
Torben

 

[flecc]

That's fine Torben, you can definitely leave it to charge in one step now. As you've said, they're not too fussy, not even bothering to quote the Beta factor of the thermistor.
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[giguana]

what cells did you use and where did you get hold of them?

 

[tourtoe]

what cells did you use and where did you get hold of them?

I bought the (noname) cells from NewTecs (germany) a year ago. I found them on Ebay.de at 5euro a piece - I paid 1 euro a piece for matching. Can't find them at that price now, though. Mine came in blue shrink with small industrial-like writing on.

They left 2 values handwritten on each cell - maybe that had to do with the matching. I have not confirmed the 11Ah yet.

I organized the pack in 2 * 15 cells - each packed in triangles 3*5 - the packs fit perfectly in 75mm ABS drain tubes available locally (Denmark). Cheap and solid solution, I think. I still need to make nice lids for them and decorate them in a way so I'm not mistaken for a suicidal bomber - they kinda have that look :-(

Cheers,
Torben

 

[HarryB]

I bought the (noname) cells from NewTecs (germany) a year ago. I found them on Ebay.de at 5euro a piece - I paid 1 euro a piece for matching. Can't find them at that price now, though. Mine came in blue shrink with small industrial-like writing on.

They left 2 values handwritten on each cell - maybe that had to do with the matching. I have not confirmed the 11Ah yet.

I organized the pack in 2 * 15 cells - each packed in triangles 3*5 - the packs fit perfectly in 75mm ABS drain tubes available locally (Denmark). Cheap and solid solution, I think. I still need to make nice lids for them and decorate them in a way so I'm not mistaken for a suicidal bomber - they kinda have that look :-(

Cheers,
Torben

Flecc what do you think of those cells sold by newtech to make up a 36V Ezee pack. Works out at £175 plus all the work and bits and pieces so maybe a little bit cheaper than the Ezee pack. The bit I am worried about the size as you have highlighted before - these are 59.3mm but the sentence ca. 1mm kürzer als Monoakkus ohne Lötfahne or approx. 1mm more briefly than Monoakkus without solder point. might be worrying.

 

[flecc]

The size is critical on the eZee case, so i couldn't really predict if they'd fit.

Cell matching is a problem with unknown cells, a mismatch possibly meaning a total failure. The problem is that it's not just a matter of voltage, but of the consistency and compatibility of content. Manufacturers of good NiMh batteries insist on using only cells from one production run in any one case, meaning lots of wastage and increased costs.

Also, powerful motors like eZee's increase the stress on cells and multiply the possibility of a failure. In fact I understand that they are having difficulty in getting consistent supplies of adequate quality, that being the main reason for the current shortage.

The US major supplier, Batteryspace, came unstuck just over a year ago with cell failures and it did their business huge damage due to adverse web publicity, so you can see it's a minefield.

The only defence I can offer is to advise careful initial charging to a bit less than full, then careful use of only three quarters of the content, gradually increasing those with each charge/discharge to run the cells into compatibility.
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[HarryB]

OK I have opened my old Li-ion battery case.

The case is 315mm long, enough for each cell to be 63mm long, so I don't think this is a tight squeeze if they are advertising the cells at 59.3mm (Germanic precision). Also Torban suggests that they do a matching service although this costs £20 more if it is needed. I have a German speaking friend so may fire off a question about batches or matching over the weekend and see where we go.


By the way there was a lot of rust marks within the battery case but I am not sure if this is water getting in and superficially marking the (bottom) cells or the battery leaking and causing the rust. Finally the bms looks different to Flecc's bms. Where Flecc's is a circuit board with heat sink mine is a black box with fins for the heatsink. Looks a bit more professional for what it is worth.

 

[flecc]

I should think that's water getting in Hal. On a couple of mine with "gappy" joins I've put a strip of silver gaffer tape over the front and rear joins, the central area being the least supported.

Your battery must be quite recent or an odd one. I got two July 2006 and one January 2007, and all are like my illustration. Seems there's a case variation too, since one of mine I just checked is 311 mm internal to the upper ridge point.

So you should be ok if the cells are indeed that size.
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[HarryB]

Just popped in 5 normal D type batteries and they slot in fine so I would have thought tagged cells would be OK as they are usually shorter. I'll let you know how I get on.

 

[Tiberius]

Hey that NewTecs site looks pretty good. I may well get some cells from there for an idea I've got. Anyone know of any other good suppliers?

Nick

http://www.newtecs.de/index.php

 

[flecc]

Thanks Hal, that certainly sounds promising.
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