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Old 03-09-2011, 08:34 AM   #1
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Location: Washington State
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Battery isolator or separator?

I recently acquired a 78 Dodge chassis TransVan that has some electrical issues. What I discovered first was that the vehicle battery wasn't charging. I removed the alternator and it passed a bench test. When I was re-installing the alternator I noticed that it appeared that the battery isolator had released it's internal smoke (pretty burnt looking) so here is my probable plan and some questions. Since this vehicle was born with an ammeter with full alternator current travelling through bulkhead connectors as well as the ammeter (which may have influenced the isolator meltdown) I plan to do this modification, Catalog and while I am at it I will install a later model 120 amp alternator and fresh heavier gauge conductors. Now here is where I could use some advice. I need to replace the deceased isolator and reading about separators (such as Sure Power 1315-200 Battery Separator) I like the features such as charging the vehicle battery first then the coach battery, being able to use the coach battery to assist starting if necessary, and if I read it correctly some models will charge the vehicle battery as well as the coach battery through the inverter when connected to shore power. Any opinions or suggestions? Thanks!

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Old 03-09-2011, 11:40 AM   #2
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For the Class A chassis, Dodge converted to a wire shunt Ampmeter in 74 (new style dash). That is actually a millivolt meter that measures the voltage drop across a section of wiring (proper name shunt). Full amperage does not go through the gauge. They only use 18 guage wires to the stock ampmeter for this style. The old full amperage gauge (pre 74 dash) has 10 gauge wires going to it. You might want to verify that they still used full amperage to the gauge on the Class C van Chassis in 78. If it is a full amperage gauge then yes, that would be a good alteration. If shunt style, then just add a voltmeter gauge and use both.

The write up says that the Sure Power 1315-200 (bidirectional) relay monitors both sides (Start & Aux battery banks). If the voltage on either side reaches the set point (13.2 volts) then the relay will close connecting both banks together. That means it does not matter which side of the relay the charging voltage is coming from. Could be the engine alternator, a converter/charger, a inverter/charger, or Solar setup. When the relay closes, both sides essentially become one battery bank. If they have a version that also allows you to manually connect the banks together (plus the automatic capability) then the manual portion would be used with a DUAL/NORM/MOM switch.
The converter in many 70's era rigs could only produce 6 amps for battery charging. This typically required several days to charge a battery. Modern Converter/Chargers and the latest rave Inverter/Chargers, typically are 3 stage models that allow much higher amp rate charging (rate controlled by 3 stage program). Example: battery has been drawn down to 50% capacity. A modern 45 amp converter/charger could intially supply 45 - house load amps to the battery (or banks if the above relay was installed) for charging. Lets say daytime house currently only needs 5 amps (you are off fishing). The converter/charger (or Inverter/Charger) can supply up to 40 amps to recharge the battery bank. The actual amperage amount is controlled by the charging program based on the battery condition. Once the banks are recharged, the converter/charger output drops to float voltage. The relay may or may not open depending on the float voltage. The relay would open when you disconnect shore (generator) power. It would close again if you started the engine or reconnected to shore power (generator).


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Old 03-09-2011, 08:58 PM   #3
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Thanks for the response Dave! I will pop out the instrument cluster and check for sure on the wire gauge at the ammeter. What I have read it appeared that it was around 80 that the class C van based units phased out the old style ammeter but that way I will know for sure and I can see if there is anything else that looks like it use some attention while I'm in there. I did a little reading on the converter/chargers and it looks like that would also be a desirable upgrade for the old girl. Mechanically the thing is sound (showing 79k for miles, and I want to think it is actual) and if I bring the electronic's into the current millennium I should be content with it. Thanks again, Abe
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Old 03-17-2011, 04:34 PM   #4
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I upgraded the convertor in my '88 Itasca last year. This was after the generator died and sent a spike to the new LCD tv and fried it. The old convertor had a large electro-mechanical coil in it.
If you want to you can install a constant duty solenoid controlled by a dash switch or a source powered up when the ignition is in the run position to charge the coach batteries off the vehicle alternator. This way you can leave the chassis system intact and it will be less likely to leave you stranded.

My Itasca has a solenoid and a dash switch for chassis, both chassis and coach, or momentary to connect chassis and coach to assist starting. This system works well and is low tech and easy to diagnosis and repair, as well as inexpensive.
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