9V NiMh battery charger

[rogerthebodger]

Any one know of a battery charger for charging PP3 9V NiMh batteries with an input voltage of 12-14 Vdc to run direct from the boat 12 V system.

I already have 12v input chargers for AA NiMh 1.2 V batteries and AA rechargeable alkaline 1.5 V batteries.

Ebay would be best due to my location.

 

[David2452]

Any one know of a battery charger for charging PP3 9V NiMh batteries with an input voltage of 12-14 Vdc to run direct from the boat 12 V system.

I already have 12v input chargers for AA NiMh 1.2 V batteries and AA rechargeable alkaline 1.5 V batteries.

Ebay would be best due to my location.

A Maha C490F will do 4 off PP3 at once.

 

[VicMallows]

All you need is a simple resistor in series to give you the charge current you want. Charge the battery at about 1/10s it's rated capacity.....probably around 18mA for 12 hours. Try a resistor of around 200-300 ohms, measure the current, and select to give you the desired charge current. NOTE THAT the current will increase dramatically when the boat battery is on charge from a charger or the alternator so be careful, or select the resistor accordingly. (A very slightly more complicated circuit can avoid this issue).

 

[rogerthebodger]

(A very slightly more complicated circuit can avoid this issue).

Do you know where I may find a "slightly more complicated circuit" may be found.

Could a LM317 be used wired as a constant current source be used?

 

[VicMallows]

Do you know where I may find a "slightly more complicated circuit" may be found.

Could a LM317 be used wired as a constant current source be used?

I would think so, though input/output differential could be getting marginal ? I was thinking of a much simpler zener circuit just to limit the voltage (and hence current).

 

[David2452]

I always understood that 9V NiMh needed close to 15v to charge to full potential, so a simple 12v with resistors would charge them poorly and very slowly, the proper thing will do it fully and much faster.

 

[noelex]

One of the "hobby chargers" (used by the RC crowd) will do what you want. They will charge just about any battery ( just check on your chosen model that the charge current goes low enough)

 

[William_H]

I always understood that 9V NiMh needed close to 15v to charge to full potential, so a simple 12v with resistors would charge them poorly and very slowly, the proper thing will do it fully and much faster.

I don't know where that figure would come from. My 12v NiMH needs about 15 volts to get a decent charge current in but would charge more slowly at a 13volts.
Vic Mallows has correctly indicated that a simple resistor should be fine. As an indication about 150 ohms should give something like 20 milliams charge current from 12v supply. If that supply goes up to 14volts on charge then current into battery would rise to something like 35 milliamps.
As said NiMh should be charged at .1 of MaH rating ie 10 hrs to put back in battery AH rating. This is considered max safe if left on charge.They can be charged faster but do not leave them on charge but remove after the capacity has been filled. Or sooner for safety of battery life.
An LM 317 does make a lovely constant current regulator. however as said you need to drop 1.25 volts in the sensing resistor and about 2.5 volts in the regulator itself so 12v supply would not be high enough for recharging 9v battery.
These batteries however are not all that successful in my experience. They do not like to be discharged too low. If one cell volatge falls to zero then subsequent current out of the battery tends to try to charge that first cell in reverse. This can result in a shorted cell which can not be rechared. With larger batteries or individual cells you can sometimes remove the short by high current flash in charge direction on the single cell. But you cannot dismantle a 9v NiMh easily to get at individual cells.
good luck olewill

 

[David2452]

I don't know where that figure would come from.

Here http://batteryuniversity.com/learn/article/charging_nickel_metal_hydride

 

[rogerthebodger]

One of the "hobby chargers" (used by the RC crowd) will do what you want. They will charge just about any battery ( just check on your chosen model that the charge current goes low enough)

Do you have a link to any "hobby chargers" you refer to like the one in your pic. Thks

 

[noelex]

Do you have a link to any "hobby chargers" you refer to like the one in your pic. Thks

This is an example of one:
http://www.ebay.com/itm/iMAX-B6-Dig...Radio_Controlled_Vehicles&hash=item4856948265

Please note I just plucked this out of ebay I didn't check if this was the best value etc.

These sort of chargers are very useful on a boat. They work directly off 12V will charge almost any battery from 1.2v-18v or so of almost any chemistry. When charging they give details about the total AHrs, current, voltage etc.

They don't come with any battery holders and they they have so many options and settings you have to be a bit "geeky" to use one. Just like me
I have so many rechargeable batteries on board for HH GPS, head torch etc. I use one every couple of days.
This is mine with a battery holder I made ( but you can buy a plastic one if you want from an electronics store)

 

[VicMallows]

Please note I just plucked this out of ebay I didn't check if this was the best value etc.

I'm intrigued that the one you happened to pluck will not ship to UK for some reason. I often use Chinese sellers and it's the first time I have encountered this. Wonder if the seller has been caught out by overzealous customs looking for CE status? ......or people refusing delivery because of the absurd Royal Mail £10 fee to collect perhaps just £1 of VAT .....and then complaining to EBAY.

 

[noelex]

I'm intrigued that the one you happened to pluck will not ship to UK for some reason. I often use Chinese sellers and it's the first time I have encountered this. Wonder if the seller has been caught out by overzealous customs looking for CE status? ......or people refusing delivery because of the absurd Royal Mail £10 fee to collect perhaps just £1 of VAT .....and then complaining to EBAY.

Yes that is surprising. There was nothing special about the one a chose it was just example.as always with ebay you need to look at the sellers rating compare prices (especially with delivery etc)

There are cheap Chinese chargers, better quality brand name units, and great quality top of the line equipment. Schultz makes the best gear, but its way over the top for what you require.

I would be inclined for your purposes to get something cheap and cheerful. If you are using it a lot you can always update to something better if you find it useful.