3rd Battery

[Hiram]

Ok I am back on track of turning the 1009 into a weekend backwoods exploring truck. As my wife is diabetic we have a nice portable fridge, and I want to add an isolated 3 rd battery to the rear. However I would like to charge the battery from the alternators. I already have switched the 24V run to the rear radio bus to 12v. If my thinking is correct, I should be able to use one of the Wrangler NW 3 way isolator switches, tied in at that location? THat would allow me to charge and flip the switch if I had the battery that supplies the 12v go dead in order to start? Or is the fact that the series connection exists going to cause sparks?

Hiram

 

[still standing still cyco]

I look forward to seeing if this works as planned. I have similar plans for the back of my M1010, although I'll be running 2-3 deepcell batteries, or possibly even 4-6 6volt golfcart batteries.I switched to a 160amp 12v alternator on top and I'm hoping I can just run a cable back directly off of the alt. Since that alt hooks directly to the front battery and nothing else I'm hoping it won't interfere with the starting batts at all. Where in Ohio are you?

 

[tim292stro]

Did I read correctly that you have converted your whole truck to 12volt?

If so, you should be able to use the radio power bus as a charging source. Make sure you use a fuse sized to protect the wire. A relay would be the easiest way to protect the truck electrical from your extra battery, connect the coil of the relay to the ignition wire from the vehicle system (the wire that goes hot when you turn on the ignition). This way when you turn on the ignition switch, it connects the battery to the radio power bus and charges it, and when your turn off the ignition it disconnects the battery from the radio bus.

You will get a spark in the relay if there is a significant difference in the state of charge of the two batteries. You really can't get around this without making hour system more complicated. For example adding current limiting resistor and a second rely to bypass it after a time delay...

As it happens, it would be easier if you still have a 24volt charging system in the front and 24volts at the radio bus. You can use a cheap step down voltage regulator from e-place to drop the 28.8volts from the running engine charging system to 14.4 voltage required for a single 12 volt battery. These cheap voltage regulators (found one for $7, look for "step down CC CV") sometimes feature current limiting which will make it act like a simple two stage charger:

• Bulk (current limited until the voltage matches the set point)
• Float (current tapers off as the voltage regulator maintains the voltage value)

This also prevents a fully discharged battery from appearing as a very high current load to the parallel batteries over the radio bus, and the current limiting keeps from burning up the radio bus wire, thus reducing the cause of arcing. You would still want to relay to the ignition wire so that it only charges your battery when the engine is running. The cheap step downs will only put out between 3-5amps, so to get enough to charge your battery you'd need several in parallel. I hear a good rule of thumb is the load plus 25% of the battery amp hours to get the C/20 rate.

There are also step-up and step-up/step-down CC/CV regulators on e-place, so you can mix an match to various effect. For example, you can use a 13Volt front battery through a radio wire bus that drops another volt (to 12volts) and boost that (step-up) to 14.4V to charge a battery. It's all in how much you want to do it yourself and how much money you have .

 

[Hiram]

Did I read correctly that you have converted your whole truck to 12volt?

If so, you should be able to use the radio power bus as a charging source. Make sure you use a fuse sized to protect the wire. A relay would be the easiest way to protect the truck electrical from your extra battery, connect the coil of the relay to the ignition wire from the vehicle system (the wire that goes hot when you turn on the ignition). This way when you turn on the ignition switch, it connects the battery to the radio power bus and charges it, and when your turn off the ignition it disconnects the battery from the radio bus.

You will get a spark in the relay if there is a significant difference in the state of charge of the two batteries. You really can't get around this without making hour system more complicated. For example adding current limiting resistor and a second rely to bypass it after a time delay...

As it happens, it would be easier if you still have a 24volt charging system in the front and 24volts at the radio bus. You can use a cheap step down voltage regulator from e-place to drop the 28.8volts from the running engine charging system to 14.4 voltage required for a single 12 volt battery. These cheap voltage regulators (found one for $7, look for "step down CC CV") sometimes feature current limiting which will make it act like a simple two stage charger:

• Bulk (current limited until the voltage matches the set point)
• Float (current tapers off as the voltage regulator maintains the voltage value)

This also prevents a fully discharged battery from appearing as a very high current load to the parallel batteries over the radio bus, and the current limiting keeps from burning up the radio bus wire, thus reducing the cause of arcing. You would still want to relay to the ignition wire so that it only charges your battery when the engine is running. The cheap step downs will only put out between 3-5amps, so to get enough to charge your battery you'd need several in parallel. I hear a good rule of thumb is the load plus 25% of the battery amp hours to get the C/20 rate.

There are also step-up and step-up/step-down CC/CV regulators on e-place, so you can mix an match to various effect. For example, you can use a 13Volt front battery through a radio wire bus that drops another volt (to 12volts) and boost that (step-up) to 14.4V to charge a battery. It's all in how much you want to do it yourself and how much money you have .

no I converted the rear bus to 12v I still have 24 going to the starter, my thought was to insert the battery isolator between the two under-hood batteries where it would be at 12v (front battery) parallel with the 3rd battery in the bed.

 

[tim292stro]

*sigh* This is why I moving my whole XM1027 to 24 volts. This 12/24 stuff gets messy quick.

Your 12Volt (low-side) alternator is going to be working much harder since it is running the whole truck (minus the starter and the glow-plugs), plus charging one of the engine batteries - and now you are thinking of adding another battery to that load. Because you have two alternators, you are spared some of the worst possible issues (charging imbalance with a single 24V alternator and 2x 12V batteries), but you still have to size the charging system properly for the load. That power needs to come from somewhere, and I'm guessing that you will have two different size batteries charging on the 12V side (the 110Ah 6TL battery under the hood, and whatever battery you use inside).

Also, you shouldn't mix battery types, for example AGM + Flooded Lead-Acid. These batteries need different charging voltages, AGM generally needs higher voltage and can accept current levels that would boil off a 6TL - killing it and leaving you stranded. You could run the lower of the two voltages and currents, but this would eventually kill your inside battery (and potentially leave your diabetic wife at risk).

You really want to add up your truck's loads (lights, fans, wiper motors, radios, etc...) and then add 25% of the 12Volt battery Amp-Hours (Ah) to get your normal alternator output current. If you are adding a battery, you want to add its 25%Ah value as well - this might mean getting a bigger alternator than stock. If you aren't producing enough power to cover those loads plus the battery charging, you will overheat the alternator (short life), and kill one or both of your batteries (short life).

The mixing of the battery types is one of the reasons I put forth the idea of using those cheap step-up/step-down regulators. You can set your alternator at the correct voltage for the primary battery it is charging, and let the set-point on the voltage regulator take care of the second battery regardless of the settings on the alternator. This doesn't get you around the need for more power though.

I don't mean to possibly come off argumentative, but we are talking about someone's health...