Charging 9.6v Ni-MH battery with 12v charger?

[amando96]

Hi, i got a 9.6v 1300 mAh Ni-HM battery pack, it has 8 cells, i don't have a 9.6v charger, but i do have a 12v and 250mA charger, can i charge it with that? it was originally made for a 10 cell 12v pack, but is it possible to charge with that? or get a 7809, and a diode, and do it from there? thanks.

 

[Dragon Tamer]

Ni-MH batterys are extremly robust and can easily handle the over voltage. In any case you want to have the voltage of the charger slightly higher than the battery's maximum voltage. If anything I would be concerned that your charger's voltage is actually too low.

 

[amando96]

Cool, thanks for the quick reply, so how long should i charge it for?

 

[antknee]

You can't really over charge batteries, they will simply stop storing the energy. How quickly that will happen is just a guess, leave them overnight and don't worry about it.

 

[amando96]

What if something bad happens, can they start a fire?

So i'm expecting it to take over 10 hours for sure? i'd rather do it in the day time, tomorrow.

 

[antknee]

I've never heard of a battery charger causing a fire. That doesn't mean its impossible it just means its very unlikely. If you're a little concerned charge it while you are around so you can keep an eye on it. A standard charge for my 9V PP3 batteries is 16 hours. Its hard to say how long yours will take, but from flat 8 - 16 hours.

 

[MikeMl]

You can't really over charge batteries, they will simply stop storing the energy. How quickly that will happen is just a guess, leave them overnight and don't worry about it.

This advice is just plain wrong! Depending on battery chemistry, overcharging can cause an explosion, start a fire, damage the battery by causing it to vent, etc.

 

[antknee]

This advice is just plain wrong! Depending on battery chemistry, overcharging can cause an explosion, start a fire, damage the battery by causing it to vent, etc.

The poster stated they are Ni-Mh with a 12V supply. Ni-Mh batteries aren't inherently dangerous. If they were they wouldn't be so ubiquitous.

As a kid I used to charge up non rechargeable batteries and heat them up on the fire to get some more life out of them! Worst that ever happened was a leak

 

[MikeMl]

The poster stated they are Ni-Mh with a 12V supply...

But you didn't. Your statement sounds like it applies to all types of batteries. That is what I'm objecting to.

 

[antknee]

I was talking in context. I don't have time to check my exact words for a wider audience...

 

[Dragon Tamer]

Only Lithium batteries tend to catch fire, in fact I prefeer not to use lithium batterys all together. For the OP charger circuit, I would supply the batteries with about 5% more voltage than the maximum of the cells. I would also add something like a 10k to 1k bleader resistor to create a trickle charge so the batteries are not constantly over welmed with voltage even after they charge.

An even better solution is to just buy a battery charger IC which will charge the batteries properly. The MAX712 is a pretty popular one (also the one that I am quite farmilliar with)

 

[edeca]

The poster stated they are Ni-Mh with a 12V supply. Ni-Mh batteries aren't inherently dangerous. If they were they wouldn't be so ubiquitous.

It is quite possible to shorten the life of NiMH batteries with a bad charger (i.e one that does not stop after charge completion or when the cell temperature is too high).

Please see my post in a different topic today for links to more information about NiMH: https://www.electro-tech-online.com/threads/nimh-battery-cells-query.107657/#post881758

 

[antknee]

I have 2 Uniross chargers, one which stops when the batteries are fully charged and the other older one which doesn't. I tend to use them in tandem so I can see when both are more or less charged. I did have a fairly new 9V rechargeable battery pop its top while in use recently. I think that is more down to the price I paid £2 ($3) than the charger.

 

[edeca]

I have 2 Uniross chargers, one which stops when the batteries are fully charged and the other older one which doesn't. I tend to use them in tandem so I can see when both are more or less charged.

Unless you can be sure that both use the same charging mechanism, how do you know this is accurate?

It is probably a good guess, just playing devil's advocate.

 

[antknee]

Lol. I just checked and they have the same output rating. I left my soldering iron on all night a while back, i'm more concerned about that starting a fire than batteries. It'd be interestng to know statistically which piece of electronic equipment/kit is most likely to cause trouble of this nature.

 

[edeca]

In a normal home? You're probably more likely to encounter trouble with faulty mains devices such as a dodgy dishwasher or wonky washing machine.

However, that doesn't mean that all chargers are created equal and it certainly doesn't mean that all charge in an optimal way. However, that strays from the original question in this topic.

 

[amando96]

Charged it for 6 hours, the battery basically didn't heat up to the touch, only the charger, already tested it out, seems like it could use more charging next time, gonna finish it off now, to not screw it up with charging without it being dead.

 

[swallow_159]

hi
when u want charge nimh battery if use low current which is less than I/4 (I = the nominal I of battery your is 1300 mah) its not dangerous coz its slow charging and dont need any cut off circut

 

[vlad777]

You should check what is the fast charging current for your battery pack.
Anything bellow that is OK.
You should have info like these slow charge time/current and fast charge time/current.
Just use linear calculation for needed time + few percent.
When batteries are charging they are fairly cold and when they are full(and still charging) they get kind of hotter...

 

[swallow_159]

when you want charge this kind of battery before preaper fast charger you need some cut off circuit for guard your battery from over charging that cause damage the battery sell or maybe burst that . NiMH batteries are damaged from overcharging. It is therefore
important to do accurate measurements to terminate the charging at exactly the right time (i.e., fully charge the battery without overcharging).