modifying 240v charger to 12v?

[sam_uk]

I am looking for a way to do a fast charge on 4 X 2.6Ah NimH batteries from a 12v source.

Ihave found that Bosch do a charger that they claim will charge in 20mins http://www.sbtooling.co.uk/chargedata.html

£50 20 min charger http://www.powertoolsuk.co.uk/webcat/de ... FC&ID=3429

However the charger is a 240v Ac input... Would it be possible to modify it to take a 12v input?

What do you generally find inside these chargers?

Thanks

Sam

PS. This is the project I am reseaching for http://visforvoltage.org/forum/6008-2stroke-hybrid

 

[bearing]

Is the voltage source the alternator?

It looks like a car alternator. A car alternator will have an open loop voltage of 100V or similar. A regulator regulates the field windings to make the voltage and current appropriate for a 12V lead acid battery. It looks like the alternator you bought don't come with a regulator.

Someone familiar with this kind of electronics can probably make a regulator suitable for a 12V, 24V or 48 V NiMH battery. (I'm not sure which voltage your pack will have since it's impossible to make a 24V 10.4Ah pack out of four 12V 2.6Ah batteries).


The Bosch charger probably contains a switch mode power supply and some sort of intelligent circuit which detects when the battery is charged. But don't try to go that route, it would be like crossing the sea to get a bucket of water. All you need to do is to put the alternator current into the battery, and stop before the battery is fully charged.

There are automotive and marine Ah-meters which counts Ah entering and leaving. One of those can be used to know when to turn on or turn of the alternator.

 

[sam_uk]

"

Is the voltage source the alternator?"

Yes

"

It looks like a car alternator. A car alternator will have an open loop voltage of 100V or similar. A regulator regulates the field windings to make the voltage and current appropriate for a 12V lead acid battery. It looks like the alternator you bought don't come with a regulator. "

Well I have not got it yet, I will make sure to get one with a regulator.

"

Someone familiar with this kind of electronics can probably make a regulator suitable for a 12V, 24V or 48 V NiMH battery. (I'm not sure which voltage your pack will have since it's impossible to make a 24V 10.4Ah pack out of four 12V 2.6Ah batteries)."

Sorry I was unlclear. If I went with the Bosch I would get 2.6 Ah 24v batteries.

http://cgi.ebay.co.uk/New-Genuine-Bosch ... 240%3A1318


Perhaps I should start from the begining and state what I want to achieve;

I want to source a 10ah battery, (and charger) that I can recharge as quickly as possible, from a 20amp 12v source, (or a 10amp 24v source) What is the best way to do this?

 

[bearing]

I think the most efficient way would be to use a 24V regulator with the alternator. Every time voltage is transformed some energy is lost.

Also, if you use a commercial charger which converts the 12V to 24V, the charger would have to supply all the current to the motor as well as the batteries. That won't be a cheap charger.

 

[sam_uk]

http://www.powerstream.com/NiMH.htm
I thought from reading this that Nimh needed a fairly sophisticated charger.

"Also, if you use a commercial charger which converts the 12V to 24V, the charger would have to supply all the current to the motor as well as the batteries. That won't be a cheap charger"

De Walt do a 12v DV in, 24v dc out Nimh charger which is available for £50. It would take about an hour and a quarter to do a 2.6 Ah battery. I was hoping to find a faster charger than this, hence the thread..

I notice that the Bosch in car charger would also take 80mins to charge a 24v 2.6Ah battery. Perhaps this is as fast as I can hope for.
http://www.power-tools-pro.co.uk/bosch-al60dc2422-72v24v-nicd-nimh-in-car-bosch-charger-p-3821.html
http://www.sbtooling.co.uk/chargedata.html

 

[bearing]

I got the impression you wanted to drive at the same time as charging. If the battery is charged at 2.6A and at the same time discharge by the motor at 15A, the battery won't charge, it will discharge but at a lower rate (15A - 2.6A = 12.4A). The charger would have to supply 17.6 A to charge the battery with 2.6A at the same time as the motor consumes 15A.

The sophisticated charger will not be able to do it's sophisticated stuff if the motor is driven at the same time it is charge.

Hybrid vehihicle batteries are held between something like 30% - 80% state of charge all the time. That is partly to avoid doing some of the sophisticated stuff which is needed only at end of charge. Another reason is to prolong battery life.

 

[sam_uk]

I got the impression you wanted to drive at the same time as charging

That was the original intention. However on closer inspection of the 1hp motor output seems insufficient to do this..

 

[bearing]

Oh I see.

But why not? 1 hp is 746W. Split that in half and you have about 360W to power the motor and 360W to charge the battery.

There is of course not 100% efficiency in the system, but that small 2-stroke can probably easely be tuned to make 2 hp if necessary.