Is the 30 amp trailer battery charging circuit isolated? - Ford Powerstroke Diesel Forum
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Old 01-17-2011, 12:35 PM
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Is the 30 amp trailer battery charging circuit isolated?

Many of us use the 7 pin connector to charge the batteries on our trailer as we tow. However, as the batteries in our trucks are very different than the trailer batteries, this can cause serious damage in a short amount of time, by over charging one battery and under charging the others.

Is the 30 amp charging circuit (part of the 7 pin connector) isolated with a diode type of system or directly connected to the alternator/battery set up? If its the later, I HIGHLY recommend incorporating a battery isolator (less than $60) to help prevent killing those ohhhh so pricey batteries under the hood!
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Old 01-17-2011, 06:33 PM
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It's on a relay that is only on when the key is in the run position.
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Old 01-17-2011, 06:39 PM
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That's actually a bad thing then. Need to put a diode isolator on it.
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Old 01-17-2011, 07:04 PM
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Quote:
Originally Posted by audiocontr View Post
That's actually a bad thing then. Need to put a diode isolator on it.
Help me out here,what's the benefit to doing so?

The last 2 times I pulled my camper,the battery was almost dead,wouldn't hold a charge for long,but never affected my truck batt's.,they're over 4 years old and working great
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Old 01-17-2011, 07:07 PM
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Wouldn't recommend it. The only benefits I can see is if you leave the truck in the run position for an extended period of time or the trailer somehow starts generating its own charge at a higher voltage than the truck. On the downside, you will loose about .5v with a diode which will make charging a bit slower.

With the factory setup, the truck and trailer batteries are essentially paralleled when the truck is running. Your electrical loads are supplied by the alternator when the truck is running, not the batteries.
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Old 01-17-2011, 07:16 PM
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That's what I thought,the relay is only on when switch is on,I knew I had enough juice for break-away stopping though ,if trailer came unhooked

After thinking about it -the only difference is the camper battery is a deep cycle,would that make that much of a difference?

Last edited by icysmooth; 01-17-2011 at 07:37 PM.
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Old 01-17-2011, 09:28 PM
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Quote:
Originally Posted by icysmooth View Post
That's what I thought,the relay is only on when switch is on,I knew I had enough juice for break-away stopping though ,if trailer came unhooked

After thinking about it -the only difference is the camper battery is a deep cycle,would that make that much of a difference?
Your break away uses a battery on the trailer, either the house battery or a smaller dedicated one. Supposed to apply full breaking for ~15 min or so.

The deep cycle battery won't matter, just uses thicker plates so it will hold up better to deeper discharges. Where it could potentially make a difference is if the trailer battery was connected to the truck battery for a significant time without the truck running. The relay prevents this.
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Old 01-18-2011, 05:52 AM
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Now i disagree. The issue has to do with over charging and under charging the battery bank. This battery bank is now composed of 3 different types of batteries when the ignition is turned on, and only one current sensing alternator. The alternator has no idea that one of the three batteries is fully charged, it sees the whole circuit as one. This is the same reasoning behind running two of the same batteries under our hoods. We use the same batteries, and replace both at the same time. Now in the case of my set up, the smaller battery will fully charge prior to the huge batteries up front, yet the alternator will still supply amperage as the TOTAL battery bank voltage is yet at max. The large batteries run the risk of not fully charging, leaving you stranded in the cold... but of most interest is what happens when you OVER charge a lead acid battery.

Here is a snippet from Wikipedia:

Any lead-acid battery system when overcharged will produce hydrogen gas. If the rate of overcharge is small, the vents of each cell allow the dissipation of the gas. However, on severe overcharge or if ventilation is inadequate or the battery is faulty, a flammable concentration of hydrogen may remain in the cell or in the battery enclosure. Any spark can cause a hydrogen and oxygen explosion, which will damage the battery and its surroundings and which will disperse acid into the surroundings. Anyone close to the battery may be injured.

Sometimes the ends of a battery will be severely swollen, and when accompanied by the case being too hot to touch, this usually indicates a malfunction in the charging system of the car. Reversing the positive and negative leads will damage the battery and may lead to gassing and explosion. When severely overcharged, a lead-acid battery gases at a high level and the venting system built into the battery cannot handle the high level of gas, so the pressure builds inside the battery, resulting in the swollen ends. An unregulated alternator can put out a high level of charge, and can quickly ruin a battery. A swollen, hot battery is very dangerous, and should not be handled until it has been given sufficient time to cool and any hydrogen gas present to dissipate.

A person handling a car battery should always wear proper protective equipment (goggles, overalls, gloves) and make certain there are no sparks or smoking close by.


I'm more comfortable with 13volts charging my trailer battery and break away than I am with the above.
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Old 01-18-2011, 01:19 PM
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It will not over charge truck batteries. I've done it for years with 2 camper batteries deeply discharged. I have a separate more accurate voltmeter on my truck and the running voltage is no different when hooked to the camper than when it is not.
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Old 01-18-2011, 02:18 PM
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Quote:
Originally Posted by coot1 View Post
It will not over charge truck batteries. I've done it for years with 2 camper batteries deeply discharged. I have a separate more accurate voltmeter on my truck and the running voltage is no different when hooked to the camper than when it is not.
Could this be because of the battery isolation mod in your signature?
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