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Old 11-14-2010, 09:44 AM   #1
Bus Crazy
Join Date: Jan 2008
Location: Upstate NY (Mohawk Valley)
Posts: 1,094
Re: How do I Charge my batteries?

Originally Posted by zenmonkk
So I plan on having a battery bank with 4-6 golf cart batteries run in series to make 12 volts. NOW, What I don't understand is what battery charger do I get? Will a 12 volt battery charger work or do I need to get a six volt. I'm gunning for a three stage 12 volt but I'm not sure. Any suggestions on a decent battery charger that wont break the bank?

I also don't quite understand how to wire everything so when the bus is running the batteries get topped off. I know its on this forum somewhere. I just get overwhelmed by the sheer amount of information I'm required to remember!
A three-stage 12-volt charger will be excellent for your purposes.

But watch how you wire the batteries. Four six-volt batteries truly in series delivers 24 volts, six delivers 36 volts. That is with one battery grounded, and the minuses of all the other batteries connected back to the plus of the one before it.

What you really want is series-parallel connection. Tie the golf cart batteries together in series pairs, one battery's minus to the second one's plus for each 12-volt string. Then connect the minus of all the strings to ground, and the plus 12-volt sides of the strings in parallel to the chargers and the loads. Be sure that you keep the connections clean and solid, or the battery strings with the good connections will do most of the work, and receive most of the charging. When the charger is off, the good strings will try to top off the weaker ones, cutting down your capacity.

Be sure you size your charger properly. Series wiring adds to the voltage, parallel wiring adds to the amperage capacity. If the 6-volt batteries chosen are 150 amp-hours each, then two in series are still only 150 amp-hours but now at 12 volts. Two of these 150 Ah strings in parallel add up to make 300 Ah at 12 volts, and three strings in parallel would add up to 450 Ah. A 15-amp charger would take 30 hours to refill a discharged 450 Ah bank, if there were no losses in the process (which there are, taking even more time). This might work for a bus used on battery for one or two weekend days, and plugged in all week in between to trickle-fill, but not for extended use. Or, the batteries might never get fully filled. Check the proposed charger manufacturer's recommendations on battery capacity.

As far as charging while driving, there are multiple ways to make the connections. The important thing is to separate the vehicle and house batteries when they are not being charged, or the full batteries will run down trying to recharge the empty ones. Also, be sure the alternator is sized large enough if you will be installing a mega-capacity house bank.

The simplest method to wire is to install a heavy-duty battery disconnect switch between the positive of the starting battery and the positive of the house bank. Or, you could use a battery disconnect solenoid controlled by a manual switch at the driver's position to connect them. You have to remember to turn the connection on after starting the bus, and turn it off before shutting down. Forget it once and you may get stranded somewhere.

There are two basic automatic ways of charging. One is to have automatic control of a heavy-duty battery disconnect solenoid joining the two battery banks, instead of a human-controlled switch. The second automatic way of charging is using an isolator.

If using a solenoid, the control wire of the solenoid is connected to the "ignition accessory" feed of the bus. This is the feed for windshield wipers, etc. which is hot only when the key is in "run" but not in "start." Unless you put in heavy enough wires to run the starter, using the "ignition" feed that powers the engine systems and is live in "start" may blow house fuses or burn up wiring. This method of wiring presumes the engine is running whenever the key is in "run," and so it connects the house bank. There are also some more expensive automatic solenoids available which will sense when the higher alternator voltage is present on the vehicle side, and connect the house batteries as long as the voltage stays high.

An isolator electrically consists of two high-current diodes that act as electrical one-way valves. They are molded into metal fins that act as a heat sink to dissipate heat created by the charging current. To install this, you disconnect the alternator's positive output from the bus electrical system, and wire the alternator to the center input post of the isolator. One of the side output posts goes back to charge the normal vehicle electrical system, and the other goes out to the positive of the house bank. When the engine is off, the one-way "valves" keep the batteries isolated. The alternator output "pushes open" the valves and charges the batteries when the engine is running. If one of the battery banks is very weak and loads down the alternator output, the diode on the good bank "slams shut" its own connection, preventing the bank from being run down "helping" the alternator. The current flows to both banks again once the surface voltage on the weak bank comes up to match the good one.
Someone said "Making good decisions comes from experience, experience comes from bad decisions." I say there are three kinds of people: those who learn from their mistakes, those who learn from the mistakes of others, and those who never learn.
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