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Old 08-06-2009, 11:43 AM   #1
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Converter vs Inverter

I'm brand new to RVs so I figure I can ask very basic questions:

What is the difference between a Converter and an Inverter and which should I have and why" I have a '95 Coachman Santara with a front and rear air conditioner, Microwave oven, coffeemaker and a 19 inch TV and it currently has a 50 amp converter.

My service tech is telling me that I have to replace my esisting Converter as it is reverse-charging my two coach batteries. ie, my positive terminals are negative and my negative terminals are positive. He showed me the negative 12 volt reading on his circuit tester but I'm not certain that I buy that.

Any thoughts from anyone on either question?


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Old 08-06-2009, 07:22 PM   #2
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I don't really have the slightest idea of what he is talking about, but if I were to measure the polarity I would put the one showing positive voltage on the positive terminal and the negative on the negative terminal. Would that be the solution? Again - I'm not sure on this one what I am talking about - baffled.

Do desulfinators reverse charge?

Hooking up a converter with the incorrect polarity would fry the rectifiers in the circuit as there could be up to 100A across the terminal, but only for an instance. I think.

Isn't reverse charging equal to discharging.

A converter converts AC to DC

An inverter converts DC to AC

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Old 08-07-2009, 08:48 AM   #3
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Hi all,

Batteries can take on a reversed polarity although I do not know the cause or reason why. I doubt that it is the Converter's fault.

If the battery has this condition it can be reversed but requires a specialized load tester/charger used in a battery service shop or automobile service garage.

Good results will depend on the battery's condition but this can be determined by the use of the above mentioned equipment by a competent tech.
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Old 08-07-2009, 08:51 AM   #4
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Hi Guys

I see now that my post was not clear. My technician is telling me that my converter is faulty and that it is charging my batteries incorrectly. That is, that it is reversing the charge so that the negative terminal of the battery is putting out the positive charge and the positive terminal is putting out the negative charge and I'm not buying it. When he attaches his multitester leads (properly) he is getting a -12 volts reading from the battery. When I use mine, I get a +12 volts reading.

By my understanding, a battery CANNOT be reverse charged. Is that correct?

CAN a converter put out a reverse charge?

As it is now, I don't know whether to admire my technician for his perception or fire him for his incompetence (or worse)

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Old 08-07-2009, 08:58 AM   #5
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You may find further answers by clicking HERE then again on the embedded link.

Study the section dealing with charging and see the list of different battery terminal voltages. With the converter disconnected you can measure the teminal voltage and see if the batteries are fully charged or at some other lower level.

I doubt you will see a reverse voltage condition, but the converter could be malfunctioning. Disconnect the converter from the battery and check its output polarity.

You can also ask questions in our Tech forum, look for RV systems.
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Old 08-07-2009, 04:57 PM   #6
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I've never heard of a converter/charger putting out reversed polarity. I hesitate to say "impossible", but it sure seems unlikely. If the tech is convinced that is the case, then it ought to be safe to reverse the output wires and motor on. But I wouldn't bet that is the case.

What make and model of converter/charger is in this 1995 coach? If it is the original, it probably ought to be replaced with a newer one anyway. Most any new one will do a better job of charging and keep your batteries healthier and last longer. It's a worthwhile $200 or so investment. Of course, if you pay the shop labor to make the swap, it quickly becomes $400 or so.
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Old 08-07-2009, 06:04 PM   #7
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I think you should start by 'firing' your tech. JMHO


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Old 08-07-2009, 07:35 PM   #8
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Originally Posted by hamdave View Post
I think you should start by 'firing' your tech. JMHO

I will post a 2nd to that thought. Sounds like a flim-flam man.


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converter, inverter, polarity

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