Tow Vehicle Charging Battery - Fiberglass RV


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Old 01-16-2011, 04:27 AM   #1
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Name: Gerry
Trailer: Boler 13 ft / 31 ft Holiday Rambler
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Question Tow Vehicle Charging Battery

I know I have seen this somewhere because I did this over a year ago and assumed it was all working....but...
I just had to put a new 7 prong plug on to same tow vehicle and the
so-called charge wire prong, in plug reads about 13V on my meter. with truck running.
Is this enough to charge my camper battery?
Let me tell you how I wired the TV.
I ran a #10 stranded wire with inline fuse just from pos. post on TV to pos post of Camper.
I remember reading all about the selinoid to insure we don't discharge TV battery but I unhook every time so not an issue.
I also just assumed if alternator was charging the TV battery that it would charge the camper battery.
Any response would be appreciated.
Gerry
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Old 01-16-2011, 07:43 AM   #2
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When you check the voltage at the wire prong then go to the TV battery and see if you have the same voltage.

Bill K


Quote:
Originally Posted by Gerry View Post
I know I have seen this somewhere because I did this over a year ago and assumed it was all working....but...
I just had to put a new 7 prong plug on to same tow vehicle and the
so-called charge wire prong, in plug reads about 13V on my meter. with truck running.
Is this enough to charge my camper battery?
Let me tell you how I wired the TV.
I ran a #10 stranded wire with inline fuse just from pos. post on TV to pos post of Camper.
I remember reading all about the selinoid to insure we don't discharge TV battery but I unhook every time so not an issue.
I also just assumed if alternator was charging the TV battery that it would charge the camper battery.
Any response would be appreciated.
Gerry
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Old 01-16-2011, 08:23 PM   #3
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Quote:
Originally Posted by Gerry View Post
I know I have seen this somewhere because I did this over a year ago and assumed it was all working....but...
I just had to put a new 7 prong plug on to same tow vehicle and the
so-called charge wire prong, in plug reads about 13V on my meter. with truck running.
Is this enough to charge my camper battery?
Let me tell you how I wired the TV.
I ran a #10 stranded wire with inline fuse just from pos. post on TV to pos post of Camper.
I remember reading all about the selinoid to insure we don't discharge TV battery but I unhook every time so not an issue.
I also just assumed if alternator was charging the TV battery that it would charge the camper battery.
Any response would be appreciated.
Gerry
Yes this will charge your battery. I've used a similar setup in the past using a vacuum switch instead of a solenoid to disconnect the TV when the engine is not running. As long as you unplug your TV battery should be OK.

Dave
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Old 01-17-2011, 10:10 AM   #4
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If you are only reading 13 volts, you aren't charging anything. A "normal" healthy battery will require a minimum of 13.6 volts, and up to about 14.5 volts in order to create sufficient electromotive force (voltage) to "push" charging current into a depleted battery. Anything less than 13.6 volts (at the trailer battery terminals) is doing nothing. The 10 ga. wire should be sufficient to carry enough current, but I suspect that you may have some poor connections, or possibly that you may need to adjust your voltage regulator output up a bit. If yours is the non-adjustable type, then you might want to consider replacing what you now have with one that can accommodate the extra demand. Remember, your feeding two batteries now, and most regulators / alternators from the factory are minimally sized and generally are not set up to handle charging more than one battery, plus supply the power demands of the TV's running and operating needs too. Checking the voltage at the TV battery, the wire prong, or anywhere other than at the contacts of the trailer battery terminals will not give you an accurate reading of voltage being seen at the point where it is needed. Other measurements won't tell you if you are getting sufficient power to cause charging when measured anywhere else along the line. Keep in mind that you will also lose a little bit of your power (voltage drop) from various connections, contacts, etc. as well. Also, if you are attempting to measure the voltage with an analog meter (the kind with a half moon graduated indicator dial and a swing needle, you are just wasting your time. Invest in a good digital multimeter. The old analog ones don't provide the degree of accuracy needed to adequately determine voltage / current readings accurately enough. And a good basic one can be purchased pretty inexpensively nowadays.
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Old 01-17-2011, 11:42 AM   #5
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I'll have to get down there and take some more readings with my multi-tester just to find out where or what connection I am loosing. I didn't think that low reading at the TV plug was enough to charge.
Thanks for the info...Gerry
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Old 01-17-2011, 05:16 PM   #6
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Don't be missled by what Casita Greg says about charging at 13 volts

My charger even attempts to charge a battery that reads 0 volts.

What really happens when two batteries are connected is that they will exchange coulombs (the better charged battery sends and the lesser charged battery receives until the voltage stabilizes at some point below the initial voltage on the better and above the initial voltage on the lesser battery. When you add a charging mechanisim the battery with the shortest wiring to the charging mechanism will charged to a voltage above the battery with the longest wiring between the two batteries.

If there is no load on either battery they will again stabilize at some at some voltage. This voltage can be, in some circumstances, equal to the charging mechanisms output voltage.

If the load attached to one battery requires more, or less, coulombs than the load on the other battery the determintion of the coulomb distribution between them begins to be complex.

IMHO
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Old 01-17-2011, 06:01 PM   #7
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I've checked this several times with two different tow vehicles and have come to the same conclusion every time. The tow vehicle does a lousy job of charging the trailer battery. It just doesn't put out the amp hours to replace what I've consumed. At best it just keeps pace with the load on the trailer battery while underway. (I run the reefer on 12v while traveling.)

I installed an amp hour meter in my Casita that tracks amp hours consumed and also amp hours returned during charging. As CD mentions, the tow's alternator sees some sort of kluged together joint voltage between the two batteries.
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Old 01-18-2011, 09:42 AM   #8
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Hey CD, have you checked your meds today? What you are talking about has absolutely nothing to do with the questions that were asked. Everyone knows that a charger will still try to charge a dead battery, but that don't mean it can do it. If the electrical load (demand) is greater than the output capacity of the alternator or charger, guess what? It can't keep up a sufficient rate of charge to replenish the battery!

Yeah, two batteries hooked up together will tend to equalize their charges between them, but that has nothing to do with the capacity to provide adequate charging voltage or current. Please think first about what the question is asking before calling somebody else full of s#!t.
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Old 01-18-2011, 11:12 AM   #9
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I don't have to think about what was asked, I just have to think about how your statement was misleading. That's all.
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Old 01-18-2011, 11:48 AM   #10
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Gerry, I am under the impression that an alternator will only deliver the amount of electricity required and not its maximum output. Your tester does not create much of a demand so you are probably OK if all your connections are clean and tight.
If my assumption is wrong I'm sure someone will correct me.
John
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Old 01-18-2011, 12:49 PM   #11
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Just what exactly is it you find in error with my statements CD? Show me the error of my ways, I'm curious (and keep the irrelevant coulombs out of it,) I await your enlightenment...

Oh, and Perry, your mostly right in that it usually isn't the alternator that's at fault, although there have been occaisions where I have seen the alternator overtaxed beyond it's capacity. It's generally with the voltage regulator setting. That is what determines the amount of charging current that is released from the alternator to the battery/load. An unregulated alternator would fry a battery in short order without proper voltage regulation. Sometimes the factory regulator setting needs to be tweaked upwards a bit to handle additional loads that the factory didn't anticipate (such as adding a second battery to the charging circuit.)

This is the only point I was trying to make, a concept which CD apparently doesn't seem to be able to wrap his mind around. Just like in a water plumbing system, if you add more appliances (load) you may need to either increase the size of the pipes (larger conductors) or increase the pressure (up the voltage) to overcome the additional resistance to flow (voltage drop). Water and direct current systems aren't all that different in theory, but perhaps a bit much for some to grasp...
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Old 01-18-2011, 06:59 PM   #12
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Thread closed

I've closed this thread and referred it to the site administrators to determine if it will be reopened. Disagreements in fact are permitted but it's disappointing to see flaming this morning on FiberglassRv.com

Feel free to debate the points, but ad hominem attacks are not permitted on this forum.

I've broken out the most recent question in a new thread:
Battery Charging: what limits the amperage to the house bank?

Regards,

Matt
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