Charging 8 volt battery


I use an 8 volt battery with my small bulldozer. I need to recharge the battery but only have a charger with settings for either 6 or 12 volts. Would using the 6 volt setting be the best choice?

When the battery is installed in the dozer, the positive terminal is grounded. Would this change the way I connect the charging leads? I feel I should still connect the negative lead of the battery charger to the negative post. Correct? Thanks.


A battery charger outputs rectified sine waves. Therefore it only produces current at the peaks of the voltages when the voltage exceeds that of the battery. In the 6V position it will act more like a trickle charger. In the 12V position it would draw too much current unless you add some resistance. You could make an adapter cable with two old headlight bulbs in parallel. I always keep my old ones with one element burned out. Just put this lead in series with one of the charger leads to the battery. Always connect positive to positive.


The 6V setting will not charge the battery and the 12V setting is too high. You can drop some of the voltage at the 12V setting as suggested, it will take some experimenting to find the right load amount. There are many alternative solutions. Here is the absolute cheapest approach for the frugal minded DIYer (pay attention to the caveats!)-


Even if you put a current limiting resistor is series with the 12 volt charger, you will have to monitor the voltage of the 8 volt battery to keep the charger from overcharging the battery. Using an accurate DVM stop charging when the voltage across the 8 volt battery reaches 9.3 VDC. Otherwise you risk a lot of outgasing and warpage of the plates.

And as Opera House stated connect negative to negative and positive to positive no matter how the dozer is wired. If charging from another vehicle keep the two from contacting metal to metal or you will get a short circuit on both battery circuits.


ah yes, I once had an MG with a positive ground system. Got a jump start — backwards.

Car actually started and ran, with the electrical system changed to negative ground for a while. The generator (before alternator days) got repolarized. Of course the battery was then the wrong polarity and got discharged very fast with the generator going the wrong way.


That site just proves that you can put anything on the internet no matter how dangerous it is. I must say that I did start a car with a toaster once, but as an engineer in that field I knew what I was doing.


I like it. But I would add a few instructions. First when you build it, connect the bulb to the HOT side of the polarized plug, not the neutral side. Second, to use it, follow the following instructions:

  1. with unit unplugged connect up the leads and the voltmeter. Voltmeter must be battery operated.
  2. Battery must be disconnected from anything else. If you can’t, make sure the golf cart or whatever is not grounded anywhere, or that nobody can touch it.
  3. Plug unit in.
  4. Do not touch any part of the circuit or battery or whatever the battery is in without unplugging the unit first.
  5. Observe voltmeter for proper charge, do not touch it.
  6. do not leave unit unattended. (can be ignored if charge rate is low enough)
  7. When done, unplug


in the toaster field? more details please.

let me guess: you used it to warm up the battery.


I had left my battery charger at my parents to charge their boat battery. Had to come up with something to charge battery or I was stuck. The circuit was similar to the circuit shown on the web site with the toaster in place of the lamp in the hot lead. A full wave bridge rectifier was used in place of the single diode. The toaster provided about 9A charge and breakfast. Kiddies, don’t try this at home.


got it. should have guessed.


Nothing wrong with additional warnings. It is not overtly dangerous if you read and follow the warnings given and use some common sense. It simply illustrates the absolute bare minimum required to accomplish the goal.