Can't for the life of me figure out how to get the batteries on my 1976 W900 charged using a 12volt charger. system has 4 6volt batteries and two isolator switches, I know I have successfully charged the batteries using a 12v charger in the past, just don't remember how I did it. people have suggested just going to two 12volt batteries in the past, but I had to get a new 12-24v series parallel switch for it and when I did the guy at the electrical rebuilder shop said I was better off with 6 volt batteries. Bob
Seems like you could open the switches, charge the 6 volt batteries in pairs with a jumper between the two batteries paired by your charger.
Not a lot of experience with 6 volt batteries but IIRC if you isolate 2 of them and connect them in series (positive to negative) and connect the charger across them as a group it should give you 12 volts. On my 1980 W900 I just bought four 12 volt batteries, put them in two pairs and connected them in parallel.
You have two strings of two 6 volt batteries. They connect at the series parallel switch and the switch uses them to "build" 24 volts only when activated by the starter circuit. The switch should be sending 12 V to the electric system all the time, easy to confirm with a $3 multimeter. Hook the charger to the 12 V terminals on the switch and then use the multimeter to check that both strings are getting the same voltage, 13 climbing towards 14V. I don't see any reason to isolate anything? Only if you want to charge a 24 volt system with a 12V charger, and then it's just hooking up to each battery separately NOT AT THE SAME TIME. Another way to look at it, take the multimeter to the alternator, check the voltage from the big terminal to ground, if it's 12V, hook up your positive battery charger clamp there.
You should have two pairs of batteries that are connected to each other permanently by a single cable from the positive of one to the negative of the other and this jumper will be connected to nothing else. Don't connect anything to the jumper. Rather, connect the 12V charger to the *other* positive and negative of each pair in question.
thanks for the replies, I was trying to jump across two batteries but I was doing it with the isolator switch(s) closed. once I opened them it worked like a charm. I'll just have to charge the batteries two at a time. the reason I can't just fire it up and charge them is that the alternator is bad and I don't have the time to deal with it right now. truck is parked at the moment and I just need to move it every now and then. thanks again. Bob
This would be the best way to charge all the batteries equally. My crane truck doesn't get a lot of use, so I have a 5 amp onboard charger to maintain the batteries and it works great for use around the yard when it doesn't get enough run time to fully charge the batteries. It's plugged in all the time and hasn't had new batteries for 12 years.
Charge the two group 31 12v's in my crawler off a pair of 12v chargers even as they are aligned in series for 24v. So long as you are connected JUST across two of the 6v batteries with the first connection on + the jumper connected -/+ and the other charger connection on the other - then all is good.
That might depend on the charger, and whether they ground the negative cable to the chassis of the charger, and whether you have a grounded power strip.
So long is a two lead charger should not make a difference.
If the chargers have the negative cable grounded to the 120v ground then it DOES matter to one of the chargers.
With 24/12 start/charge have to make any charger connection direct to the batteries, nothing to frame grounds.