Powerstream chargers

[jha07]

I’m considering getting a charger from Powerstream and have been checking out the specs of their 36V and 48V 2A NiMh charger. Both chargers use thermistors to detect peak charge, and does not check for voltage drops in the pack. Both chargers have a peak voltage output of 56V and a max power output of 140W. In fact, the specs on both chargers are identical, expect for the number of cells.
Since the two chargers seem identical, I’m wondering if the 40 cell or the 30 cell charger can be used to charge a 35 cell pack. The fact that the 30 cell charger also has a 56V peak output makes me think it should be fine. And since the charger doesn’t check for voltage drops in the pack for peak detection, I don’t think the number of cells should matter too much.
Does anyone have any experience with these chargers?

 

[jha07]

I decided to give it a try and got the charger.
But I’m a little confused. The battery plug that comes with the charger is different than what I need, so I have to put a different connector on. But I don’t know what the color code on the wires mean. I’m hoping someone here might.
The three wires are Brown, Blue, and Yellow.
Which color is Postive, Negative, and NTC?

 

[Jeremy]

Your best bet would be to check the output with a meter. The cable is mains cable, so the colours don't mean much! I found that on my Chinese charger the blue was the positive, the brown was the negative, which confounded me a little as I was expecting it to be the other way around.

Jeremy

 

[Tiberius]

It may not be as simple as that. The one I had (different make admittedly) wouldn't put the supply on until it had found the thermistor and some battery volts. Can you work it out from any diagrams and the old connector?

Nick

 

[flecc]

The yellow is the thermistor on Powerstream chargers, connected between that and the blue ground connection. Brown positive of course. On most three pin connectors the centre pin is the thermistor connection.

I use the 36 volt version to charge 33 cells/39.6 volts successfully, and you'd almost certainly be successful with 35 cells. The cut off on 33 cells occurs at a voltage of just over 49 volts, so plenty of headroom for your extra two cells.

This is the charger type I'm referring to.
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[Jeremy]

Brown positive of course.

A very bold statement!

I assumed this and then, very luckily decided to just do a quick check before plugging in. Very glad I did, as it turned out that for my charger the brown was the positive!

Personally I wouldn't trust any of the wire colours in any of this kit, they seem to often pick a colour at random, as far as I can tell.

Jeremy

 

[flecc]

It is Jeremy. By extracting that part, you gave it a different context. Following the preceding sentence it's context is very different, brown being the only colour left. I'm also used to Chinese unpredictability with colour codes and have regularly posted as such in here, and on one of my websites more than a year ago.

In this case though, I'm very familiar with these Shenzhen chargers and their output lead, together with it's sole variation in accordance with convention, as you'll see on my site links below:

One

Two

Three
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[jha07]

Thanks. The charger seems to be working now. I don't have any thermistors at the moment, so I had to trick the charger with a 10K resistor.
My only concern is, before finally getting the wiring sorted out, I was messing around with it and hooked up the yellow as the positive. The yellow has 5V on it, while the other lines didn't have anything, so I just assumed it to be positive. Anyhow, I hooked it up to the battery, >+36V, and of course it didn't work. Nothing happened, no smoke or firework. But I'm just worried I might have done some damage to the charger.

When the charger is charging, I can hear a pulse in the battery, like every second. And the fan also changes in speed in synch with the pulse. Is this normal?

 

[flecc]

The fan speed does fluctuate on these chargers, so that might not mean anything. However, there is a strong chance that 36 volts into the 5 volt thermistor circuit has caused damage, though it could well have left the main charging circuit unharmed, so worth continuing to use it and see if the thermistor cut-off operates ok once one is wired in.

There are three cut-offs though, thermistor indicated temperature rise (dT/dt), a peak permitted temperature cut-off at 50 degrees C, and a peak voltage cutoff equivalent to 1.59 volts per cell with the indicated number of cells. As long as you are using the same number or more cells than indicated, the battery will be protected even if the thermistor circuit fails the first two cut-offs.

Suitable thermistor values for this charger in generic charging are R=10k, B=3950, the Beta value not very critical.
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[jha07]

I think I might have lucked out and not damaged anything. I put a POT in place of a thermistor and slowly decrease the resistance til the charger stopped charging. The resistance of the POT when this happens is around 3.1k. That's about 50 degrees for a 10K thermistor.

 

[flecc]

That's good, they're even tougher than I thought. They are certainly more reliable than most, and a bargain price these days.
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