2nd_apprentice
Well-Known Member
Is there such a thing for size "D" batteries?
Can only find AA and AAA chargers for DC
Can only find AA and AAA chargers for DC
12 Volt Battery Charger
- Thread starter 2nd_apprentice
- Start date
pcatterall
Well-Known Member
There certainly WAS as I had one a few years ago! Maplin?
FrankieJ
Active Member
These guys have them, but they aint cheap. thttp://www.tantronics.co.uk/acatalog/ansmann_powerline_5_mobile.html
albineer
Well-Known Member
Uniross do them. I bought mine in Homebase. I think Amazon list them too.
Edit
I ought to have followed pcatterall's suggestion and checked Maplin first. They are cheaper than Uniross
Edit
I ought to have followed pcatterall's suggestion and checked Maplin first. They are cheaper than Uniross
William_H
Well-Known Member
Assuming you want to charge rechargeable D sized batteries then any charger will do the job if you get from Maplins or similar D sized battery holders. You can simply solder wires to connect the new holder in paralell with the holder for any other sized battery.
Bear in mind that the Amp Hour rating of the D cell will dictate the charge time. So a 4AH D cell will take twice as long to recharge as a 2000maH AA cell.
Now if you want to recharge off 12V you need cell holders and a suitable resistor to limit the current . The charger will not be automatic but is certainly cheap.
The calculation of the resistor value depends on the Amp hour rating of the cell. The usual charge rate is 10% of AH rating. They need 14hours to recharge. This rate is considered safe if the cell is left on charge long term. Any faster can damage the cell if it is not turned off after it is charged.
So a 4 AH battery should be charged at .4amp. How many cells do you want to charge. Each cell drops 1.2 volts. So eg 4 cells drops 4.8 volts.
So we need a resistor which will drop the difference between our 12v supply and our battery to be charged. Now unless you are sure you will not charge with the engine running or battery charger on you should assume 12v is really 14 volts.
Ohms law then gives us the resistance value is equal to the voltage divided by the current. So for 4 cells our voltage is 14 minus 4.8 = 9.2 at a current of .4 amps in our example gives a resistor of about 24 ohms.
One last calculation of current times voltage for the resistor gives the power dissipation of the resistor. In this case 9v times .4 amps = 3.6 watts. That means you need a ressitor that can handle at least 5 watts and it will get hot. So keep it in free air away from plastic etc. A higher powered resistor or 2X 12 ohm in series or 2x 48 ohm in parallel (all 5watt) will reduce temperature and increase power capability.
Unlike light bulbs a higher power rating of a resitsor does not mean it uses more power just that it can do so without getting overheated. It is the resistance the current and voltage that dictate how much power is wasted. Here endeth the lesson. olewill
Bear in mind that the Amp Hour rating of the D cell will dictate the charge time. So a 4AH D cell will take twice as long to recharge as a 2000maH AA cell.
Now if you want to recharge off 12V you need cell holders and a suitable resistor to limit the current . The charger will not be automatic but is certainly cheap.
The calculation of the resistor value depends on the Amp hour rating of the cell. The usual charge rate is 10% of AH rating. They need 14hours to recharge. This rate is considered safe if the cell is left on charge long term. Any faster can damage the cell if it is not turned off after it is charged.
So a 4 AH battery should be charged at .4amp. How many cells do you want to charge. Each cell drops 1.2 volts. So eg 4 cells drops 4.8 volts.
So we need a resistor which will drop the difference between our 12v supply and our battery to be charged. Now unless you are sure you will not charge with the engine running or battery charger on you should assume 12v is really 14 volts.
Ohms law then gives us the resistance value is equal to the voltage divided by the current. So for 4 cells our voltage is 14 minus 4.8 = 9.2 at a current of .4 amps in our example gives a resistor of about 24 ohms.
One last calculation of current times voltage for the resistor gives the power dissipation of the resistor. In this case 9v times .4 amps = 3.6 watts. That means you need a ressitor that can handle at least 5 watts and it will get hot. So keep it in free air away from plastic etc. A higher powered resistor or 2X 12 ohm in series or 2x 48 ohm in parallel (all 5watt) will reduce temperature and increase power capability.
Unlike light bulbs a higher power rating of a resitsor does not mean it uses more power just that it can do so without getting overheated. It is the resistance the current and voltage that dictate how much power is wasted. Here endeth the lesson. olewill
2nd_apprentice
Well-Known Member
Fantastic, found the "super universal charger" at Maplins for 9.99!
