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Using car's engine to charge marine battery??

Old 09-30-2011, 02:47 PM
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FlyWheel
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Default Using car's engine to charge marine battery??

This is crazy idea #37

Assuming both the car's battery and the marine battery are the same voltage so the engine's regulator will work properly, here is what I am thinking...

Connect jumper cables to both terminals of marine battery. Connect other end of "hot" (usually positive) cable to hot terminal of car battery. Leave ground cable disconnected and safely away from any metal part of the car. Start car.

Disconnect ground terminal of car battery (effectively disconnecting the car's battery from the engine); engine is now running on alternator alone.

Connect ground cable from marine battery to a metal part of car, completing circuit and let car engine run, charging marine battery. Car regulator will stop charge when battery reaches correct voltage (usually 12 volts).

Comments?
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Old 09-30-2011, 05:01 PM
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Glacier Girl
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On newer vehicles, to do so can often blow out the computer.

And in some cases the alternator will not function if it is not seeing battery voltage, will shut down, and so will the engine.

Also a fully charged battery is well over 12 volts. The alternator is usually putting out 14+ volts. And at low rpms you will not see much of a charge rate.

Newer style auto systems are not like the old ones. They even incorporate temp sensors for the battery. I know for a fact our Wrangler has it. If the sensor reads the temp of the battery is getting too high, it will shut down the alternator until the battery temp drops.

Really to do it like this, you would have to pull the auto battery (engine not running) install the marine version, then take a good long trip.

Or install the marine battery in parallel with the auto battery, use an isolator, and then the alternator will feed the lowest battery, and can switch back and forth as needed.

Or just break down and buy a battery charger. With the price of gas now, those couple of gallons to run the car long enough to charge the battery would pay for a small charger and the electricity to run it.
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Old 09-30-2011, 05:30 PM
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CHELLIE
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Dont Do It You Will Burn out your Alternator and Computer, Like GG Said, buy a 12v battery Charger, you can even get a 12v to 110v converter, that will run your 110v to 12v car battery charger from your car, Never disconnect a ground cable from a vehicle with an Alternator that running, you could do that with the older 12v generator of old cars, but not with an Alternator
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Old 09-30-2011, 09:00 PM
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kyleservicetech
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Originally Posted by FlyWheel View Post
This is crazy idea #37

Assuming both the car's battery and the marine battery are the same voltage so the engine's regulator will work properly, here is what I am thinking...

Connect jumper cables to both terminals of marine battery. Connect other end of "hot" (usually positive) cable to hot terminal of car battery. Leave ground cable disconnected and safely away from any metal part of the car. Start car.

Disconnect ground terminal of car battery (effectively disconnecting the car's battery from the engine); engine is now running on alternator alone.

Connect ground cable from marine battery to a metal part of car, completing circuit and let car engine run, charging marine battery. Car regulator will stop charge when battery reaches correct voltage (usually 12 volts).

Comments?
Nope, don't do it.

I just set up a 3.5 Hp Briggs gas engine with an alternator for a high power DC supply at the field. (http://www.wattflyer.com/forums/showthread.php?t=63918) And during selecting a rebuilt alternator for this project, I found that many of them indicated that their warranty will be void if they are run without a battery connected.

If you want to field charge your marine battery with your car engine, just connect the marine battery in parallel with the auto battery with a very heavy copper cable, not some aluminum set of cheap jumper wires from Wallyworld.

The way this works out is the auto battery will be fully charged, so will take very little of the alternators ampere output. But parallel connecting the auto battery with a discharged marine battery, 95% of the alternator current will travel to the marine battery. This can easily be verified with one of those Sears Craftsman #82369 AC and DC clamp on ammeters.
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Old 10-01-2011, 11:11 AM
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Dennis, maybe I'm wrong, but doing it that way, would not the Marine battery pull down the auto battery first, so they have equal voltage. Then the alternator would be having to split it's feed to both?
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Old 10-02-2011, 02:09 AM
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kyleservicetech
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Originally Posted by Glacier Girl View Post
Dennis, maybe I'm wrong, but doing it that way, would not the Marine battery pull down the auto battery first, so they have equal voltage. Then the alternator would be having to split it's feed to both?
Good question!

Unfortunately I don't have a decent pair of lead acid batteries to verify this, since both of my deep cycle batteries have quit.

But, here is what I think will happen. With the engine off, the Auto battery will be fully charged, and its voltage will be about 12.5 Volts or so. The extra battery will be somewhat discharged, so its voltage will be less than 12.5, perhaps 12.2 Volts DC.

Now, when you connect the two batteries in parallel, the auto battery will discharge into the extra battery. But that changes when the auto engine is started, and the auto alternator boosts the voltage of both the auto engine and the extra battery to perhaps 13 to 13.5 Volts DC, depending on how big the alternator is, temperature and so on.

Since that auto battery is fully charged, boosting its voltage above the 12.5 Volts full charged value it won't take much current. But the extra battery will. That is if you've got #8 or #6 cable between the auto battery and the extra battery.

It would be interesting to check this out with a Sears Craftsman #82369 digital AC and DC clamp on ammeter.
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Old 10-03-2011, 02:58 PM
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Here is a solution that is safe and will work. Go to an RV dealer, or a dealer that sells large boats. Ask them for a battery isolator. This item is used in RV's (and boats for that matter) to allow 2 batteries to be used. Both batteries are charged from the alternator when the engine is operating, but the engine does not discharge from the second battery (used for cabin power in RV's and boats) and the second battery does not discharge the main car batery.

This is a low dollar item, about $35 last time I looked, and very easy to install.

It will protect your computer and car system.

Cliff
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Old 10-03-2011, 03:20 PM
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good post here Cliffn< I use those on my boat,,4 of them for the 5 house (cabin & running lite's) and one "starter batt " for the motor,,,Didn't thing about them as a RC accessory!! good call, your bubsteve
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Old 10-03-2011, 04:26 PM
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Default Here's another way to isolate

My 97, PS Diesel, F-250 Ford truck is factory wired for a trailer. I thought I could plug into the trailer connector for my RC charger, like I have on other vehicles. I found there is a continuous duty relay, wired so the power to the RV battery is cut off if the engine is not running, if it is running then the relay pulls in and you have power.

I have added this to a couple of our older trailer pullers, but didn't expect to find it factory wired. These relays were less than $10 at a parts store.

Wired in this way, you don't lose the voltage drop across the diode, like you do with a battery isolator. So the batteries receive a full charge. Maybe the new isolators are better than the first generation, but I didn't like losing 0.6 Volts off the charge. I think that may put a lead/acid battery down to 80% or around there. You also do not get the back surge current of the RV battery trying to start the engine, like you do if the RV battery is hard wired to the main units. (isolators stop this also)

In my humble opinion, if you want to isolate batteries, a relay is a better choice. It is more wiring than the isolator, but I want a full charge.

My truck is my aircraft carrier, so I installed a 6 gauge wire with a 40 amp fuse, direct from the dual huge batteries, to the left rear corner of the bed, I have a rack of 3 chargers mounted on a board, and can charge 5 Lipo's at once, and there is still room to plug in a friends charger. My Astro 109 reads battery input voltage, if it is not in use, so I know if I have pulled down the truck batteries. I have been at the fields all day, charging many Lipo's, and the diesel has never hesitated in any way to start.
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Old 10-03-2011, 05:14 PM
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kyleservicetech
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Originally Posted by Wildflyer View Post
Wired in this way, you don't lose the voltage drop across the diode, like you do with a battery isolator. So the batteries receive a full charge. Maybe the new isolators are better than the first generation, but I didn't like losing 0.6 Volts off the charge.
I wondered about those battery isolators, the one in my old deceased motorhome used a diode isolator. The house battery never really got fully charged.

As for diodes, high powered units are available. Check this one out

http://www.newark.com/vishay-formerl...0ac/dp/07B3131

(That is 3800 Amps, they exist up to near 10,000 Amps! So much for little electronic parts)
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