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Old 05-28-2013, 10:31 PM   #11
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Originally Posted by 38FLCamper View Post
I would use a meter and check pin 4 on your TV to make sure your vehicle is putting out 12 volts and charging your batteries when running. Sounds like it is possibly not putting out any charge line.

I will check that out. Thanks
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Old 05-28-2013, 10:35 PM   #12
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Thanks it 110 thinking a second battery. I was wondering it they make a high output alternator.
The problem with alternators is that it can't tell you have a trailer deep cycle battery. It is a single stage charger that works off the average voltage across the truck. Once the truck battery is "full"; it tapers the current off. It is OK for keeping a full battery full (and even some light charging duties), but replacing a 40 amp draw is just not possible. Here is a more technical reason why it won't work even with a "heavy duty alternator."
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Old 05-28-2013, 10:48 PM   #13
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Originally Posted by herk7769 View Post
The problem with alternators is that it can't tell you have a trailer deep cycle battery. It is a single stage charger that works off the average voltage across the truck. Once the truck battery is "full"; it tapers the current off. It is OK for keeping a full battery full (and even some light charging duties), but replacing a 40 amp draw is just not possible. Here is a more technical reason why it won't work even with a "heavy duty alternator."
Herk you make it easy even for dummies like me. THanks for all your help.
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Old 05-28-2013, 11:08 PM   #14
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Herk you make it easy even for dummies like me. THanks for all your help.
There is danger in trying to simplify complex math and/or physics to make the general concepts easier to understand. "Close enough" works for most folks, but there are always purists who will jump in with a "not so fast."

As long as you get the gist of what is going on, I feel it is close enough for government work...

You really don't need to know how to build a clock to tell the time.
(Although if you want to know how, I can show ya!)
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Old 05-28-2013, 11:18 PM   #15
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I agree !! Thanks for making to easy.
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Old 05-28-2013, 11:37 PM   #16
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[QUOTE=38FLCamper;387037]I would use a meter and check pin 4 on your TV to make sure your vehicle is putting out 12 volts and charging your batteries when running. Sounds like it is possibly not putting out any charge line.

This should definitely be checked. In this case "some" is better than "none".

If the truck's charge line is not functioning, a 40 AH draw will kill a fully charged battery in a couple of hours. WITH the charge line you might just get enough extra juice to get you to your destination before the camper's battery is dead.

Here is how to figure it out.

Suppose you have a 100 amp hour battery that is fully charged when you leave (big assumption I know, but you have to start some where).

Now you pull 40 amps out to run the camper and the inverter (500 watt load).

Using the attached graph, you will see that a 100 AH deep discharge battery simply can not serve up that much power without a severe reduction in the ability to continue to serve it up. (trying to think of a good example here - maybe like trying to suck the juice out of an orange. At first there is a lot of juice, but even though there is a lot more juice in there you have to work harder and harder to get the deep juice out and the rate at which you can get the juice drops off. That sucks but it is the best I can do on short notice.)

So anyway, using the graph and a 40 amp draw on a 100 AH battery, you will see that the ACTUAL capacity is reduced to 48 AH and NOT 100 AH (Calculated with a 5 amp load in the example). (Known as the the Peukert Effect - see article)

So at 40 amps, the battery will go from fully charged to fully dead (voltage below 10.5 volts) in 40 amps into 48 amp hours or 1.2 hours.

Now, in your case, I am sure you don't have a 100 AH battery so the time would be much less. However, the 40 amp draw is not all the time; only when the compressor/heater (whatever is in your fridge) is drawing power.

So say it is only on 1/4 of the time; BUT it is at the full 40 amps. Now it gets a bit dicey since the battery can start to recover between hits (some juice can leak out of the deep pulp and be available again).

However for simplicity, lets say the average time will be 2 times longer than the "all the time on" or about 2.5 hours to a dead battery. Add some "add" from the ruck's charge line and you might get 4 -5 hours before dead.

Was that helpful?
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Old 05-28-2013, 11:52 PM   #17
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High Output Alternator

Quote:
Originally Posted by jlgail4309 View Post
Thanks it 110 thinking a second battery. I was wondering it they make a high output alternator.
They are expensive. It puts out 300 Amps

MG Industries Inc.
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Old 05-29-2013, 07:08 AM   #18
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It could be how the inverter is wired too. If it has a fairly long 12v run with undersized wiring, the voltage drop will be such that the inverter will shut down well before the battery is dead as the 12 volts will seem artifically low to the inverter.
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Old 05-29-2013, 08:27 AM   #19
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...
A pair of 100 AH batteries would do the trick.

Trojan Battery Company
You certainly can't come to that conclusion unless you know how long he intends to drive in this configuration.
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Old 05-29-2013, 08:31 AM   #20
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It could be how the inverter is wired too. If it has a fairly long 12v run with undersized wiring, the voltage drop will be such that the inverter will shut down well before the battery is dead as the 12 volts will seem artifically low to the inverter.
Good point, although that would buy him just a bit more time at best.

Another thought. In a different thread just like this, someone suggested that the inverter be installed in the tow vehicle and then run a 120v "extension cord" back to the RV to
power the fridge. With that configuration a larger alternator can definitely power the inverter as long as needed. You'd just need to be careful not to drain the truck batteries when you shut the truck off.
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