Charger compatibility

[francoishay]

Will a charger with 7.5V and 2000mA output work for a 7.2V 4000mAh battery?

 

[Centurio]

Hi,

It depends. You need to provide more information. If its a li-ion pack, so it might be a 2s (two cells in series). The nominal voltage might be 3.6V -> 2x 3.6V = 7.2V. But fully charged = 2x 4.2V -> 8.4V.

If you look closely at the output of your charger, you might find the output voltage printed somewhere. If you can, you are better off with measuring the output voltage of your charger. If it is really 7.2V only, you will charge your battery only a little.

Hope you can understand what I mean.

 

[francoishay]

I haven't bought the battery yet but according to the ad is is "High Capacity Security 7.2V 4000mAh Rechargeable Low Self Discharge NiMH Battery Pack". The charger I have, used to be for something else and I measured it to have an output of 8.3V but on the charger it says it has an output of 7.5V and 2000mA.
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[francoishay]

Would it be fine?

 

[john61ct]

7.2Vnominal implies LI and 2S

so charging voltage is 8.4V max

Anything below 8.1V won't get anywhere near full

3.75Vpc is like a storage charge, might be around 50% full.

 

[999zip999]

Never never believe the printed words on the side of the charger get a voltage meter and check it they're all over the place some 5 volts will 8 volts to some 5 volts go 7 volts some 5. Or always check ? Always.. get a cheap little rc charger. Go charge it outside at first as it hard to set there and monitor.

 

[francoishay]

How important is the 2000mA output compared to the 4000mAh battery? And what voltage would be recommended for a battery like the one above?

 

[john61ct]

I gave you the voltage range above.

Higher end gives a bit more range but not optimum for longevity.

Your amps rate is 0.5C if accurate and that is fine, from near empty 90min to 2 hours charge time

 

[serious_sam]

7.2Vnominal implies LI and 2S

It's NiMH, not lithium...

High Capacity Security 7.2V 4000mAh Rechargeable Low Self Discharge NiMH Battery Pack

For NiMH, you really should use a NiMH charger that uses a specific charge algorithm.

Alternatively, you can relatively safely "float charge" at about 0.1C and 1.4V per series cell for approx 15 hours (in your case 400mA and 8.4V (6x1.4)). Try to ensure that the pack is drained at the start, or you start to do small damage for keeping it on float for too long.

Will a charger with 7.5V and 2000mA output work for a 7.2V 4000mAh battery?

No, IMO your charger is not suitable.

Anyway, unless you have a specific reason for NiMH, lithium is usually a better option these days.

 

[tmho]

I haven't bought the battery yet but according to the ad is is "High Capacity Security 7.2V 4000mAh Rechargeable Low Self Discharge NiMH Battery Pack". The charger I have, used to be for something else and I measured it to have an output of 8.3V but on the charger it says it has an output of 7.5V and 2000mA.
[/img]battery.PNG[/img]

You mentioned the measured output of the charger is 8.3V. If that is true, then it is suitable to charge the battery.

 

[amberwolf]

If you have a NiMH battery (or NiCd), you need to use a charger specific to that chemistry and that number of cells, that can read the temperature sensor in the pack, and so it can detect the voltage drop that happens when the cells reach full.

If you don't, you risk a fire from the pack continuously overcharging.

The NiMH pack will drop in voltage when it reaches full, unlike lithium, lead-acid, etc. When it does so, the energy difference between the voltage it was charged to and the voltage it drops to will turn into heat inside the cells.

A charger that doesn't know this is going to happen, will keep trying to charge the pack, and keep making hotter and hotter, which even if it doesn't melt or burn anything will still damage the cells. But if it kept charging it and it did keep rising in temperature, could eventually explode the cells and they could start a fire, if the charging current is high enough.

Based on the voltage reading and marking you have on your presetn "charger", it is probably not actually a charger, but just a power supply (wallwart), and has no internal regulation, and could damage *any* battery you hook it up to (or the battery load could damage *it*, even potentially overheating it and starting a fire inside it).


A proper NiMH charger will detect both the voltage drop and the temperature change (delta-V / delta-T) and stop charging if either one happens.