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Old 06-08-2009, 17:30   #1
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AC-DC Converter

My battery charger is hooked up to my ac-dc converter.
If I want to run my lights from shore power, my charger needs to be on or my lights won't work.
I've tried to unplug the charger(newmar) and turn on the lights and they won't work.
I made the mistake of leaving my converter on for a weekend and fried my batteries.
Is this the correct way to have your charger hooked up?
I bought my boat from the original owner,but unfortunately he had a severe stroke and is unable to help.
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Old 06-08-2009, 17:48   #2
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I'm not really sure what you are doing so I will make a guess at it.

You really need for a battery charger to have an actual battery in the circuit. You could buy a smaller car battery in the mean time until you replace the larger batteries that burned up. This is provided you do not need to run any large loads off the small battery when the charger is not on.

An alternative would be for you to purchase a 12VDC power supply with sufficient current to power whatever it is you need powered.

How did your "converter" (inverter or charger?) destroy your batteries? You need to find the problem before installing replacement batteries.

I would just go ahead and find the problem, fix it and then replace the original batteries that burned up. This way you are not reliant on shore power 100% of the time.

There are lots of good books on boat electrical systems that would be of help.

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Old 07-08-2009, 12:49   #3
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My battery charger didn't shut off when the batteries were fully charged.
My fridge also runs off the batteries.So if I want cold drinks without using ice I need to figure out a way to run my system from the converter.

I have purchased 2 new batteries and shut off the battery charger which lets me run my lights and fridge when needed, and protects my batteries from being overcharged.

My question is why can this not be done using my ac-dc converter switch?

Is it common to have a battery charger on this line?
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Old 07-08-2009, 13:58   #4

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"My battery charger didn't shut off when the batteries were fully charged."
It sounds like you are using an automotive charger for your batteries--and that's not suitable for a boat.
A proper three stage marine charger doesn't ever actually "shut off", instead it charges at different rates depending on the state of the battery. When the battery is fully charged, it goes to a "float" rate which pretty much can go on for months without doing any harm.
You'll also hear claims for 4-stage and 5-stage chargers, but in reality that's just a numbers game.

So part of the question is how big is the boat, how much batterry capacity do you carry, and what kind of charger are you using?

The dock AC power should be feeding a battery charger, which feeds your batteries, which in turn feed a DC-to-AC inverter to provide AC onboard (when away from the dock) as well as the 12-volt systems like the boat's lights. The inverter may or may not be permanently wired up, there are options depending on price and purpose there too.

But if you've got a cheap auto-style battery jump-start charger...that's just the wrong equipment for a boat.
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Old 08-08-2009, 10:29   #5
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Well, there is a lot to your question. I agree a good book on DC systems will help you.

First, the battery charger (I believe this is what you were referring to as an "AC to DC converter") should be permanently wired to charge the batteries. This means that when the charger is plugged into AC power, it is supplying current to all of the DC loads on your boat. This includes the lights, refrigerator, radio, etc.

(To head off some other postings on this, a purist may say the current comes from the batteries, and the charger recharges the batteries. Until we can trace the paths of individual electrons, this is not worth arguing about.)

The type of battery charger you have will depend on how you use your boat. I had a boat once with a Newmar charger, and it did not fry my batteries when left on. If yours did fry your batteries, you have a problem that needs repair.

Second, I understand you want cold drinks in the fridge, but a refrigerator will quickly drain you two new batteries unless you have something to keep them charged. While at the dock, this will be your battery charger.

So, trying to directly answer your question about the "AC to DC Converter switch" - you should not have to operate any switches on your battery charger to run your refrigerator or your lights. The battery charger you have should be able to handle variations in load (for example, as the fridge cycles on and off) without you turning it on or off. You should be able to leave the charger on without fear of damaging your batteries. If you can't do this, you probably have a problem with the charger.
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Old 26-08-2009, 18:34   #6
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Thanks for your help.
I have a Newmar ABC 12-15 2 bank charger that is more than likely not working properly.
I ordered a Newmar PT-25 as a replacement that will be arriving tomorrow.
This hopefully will solve my problem and allow me the option of adding an extra battery if need be.
I'm not sure of the age of the original charger and didn't want to take a chance on having it fixed.
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