Second Battery?
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500, 472, 425, 368 Discussion, Second Battery? in Cadillac Engine Technical Discussion; Has anyone tried hooking a battery isolator to the stock generator of a 69 472 to charge a second battery ...
  1. #1
    Sasquatch's Avatar
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    Second Battery?

    Has anyone tried hooking a battery isolator to the stock generator of a 69 472 to charge a second battery for lighting and stereo while sitting? Thinking about doing this in the hearse. Can I locate the battery "in" the car under the storage space in the back of the hearse or do I have to worry about ventilation of battery fumes? Thanks.

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  3. #2
    zbgsaa is offline Cadillac Owners Member
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    Re: Second Battery?

    just get a drycell battery so u dont have fumes to worry about

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    Sasquatch's Avatar
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    Re: Second Battery?

    Being that this is a generator/voltage regulator set up will that make a difference? Will the voltage regulator work properply?

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    DaveSmed's Avatar
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    Re: Second Battery?

    The old mechanical regulator? Yech. Might I suggest considering a newer 10 or 12SI alt? MUCH more efficient, easier to replace/find parts for, and you get to eliminate a bunch of wires from under the hood, if you opt to do so.

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    Sasquatch's Avatar
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    Re: Second Battery?

    Yeah everythin there is still stock. Generator with the seperate regulator mounter to the passenger side wheel well. Dave sounds interesting can you elaborate on wire reduction and where to find this alt.? I was thinking even a dual output alt. and just run one output to each battery. Any ideas on where to find one. Either that or a battery isolator. Thanks.

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    DaveSmed's Avatar
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    Re: Second Battery?

    Just about anywhere has the alt in stock. A 10SI 63 amp alternator that would work well on your car has AC-Delco P/N: 321-43 Or, if you go the parts counter route, get one for a '77 Pontiac Grand Prix, 350 VIN R engine, with Air COnditioning, and Heated back light (rear defogger). The alt has three wires, one to the battery, one runs to the old mechanical regulator harness (controls the idiot light) and one is the remote sensing wire. Neat feature, but for simplicity, you can connect it right to the batt lug. The good part about these alternators is availability. almost every aftermarket "street rod" alternator is based off the same design. That means, if so inclined, one can buy one in a pretty chrome case.

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    DaveSmed's Avatar
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    Re: Second Battery?

    As far as the isolator, if I understand correctly, there nothing more than a big diode? Not sure what an isolator would run, but it should be pretty easy to come up with a way to disconnect one of the batteries automatically when the ignition is off. (wonder what the duty cycle of those ford starter solenoids is... could get one of those for next to nothing...)

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    Sasquatch's Avatar
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    Re: Second Battery?

    So then get rid of the regulator all together? Just still plug in the harness for the idiot light? I have not looked at it yet. Is there a connector I'll need in order to plug in the old harness?

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    Colt D is offline Cadillac Owners Member
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    Re: Second Battery?

    Sasquatch, Dave Smed helped me out with a similar issue on my '68. Here's the link with pictures. 68 Cad Wiring Problems

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    Re: Second Battery?

    Take a look @ M.A.D Electrical...there are some awesome pages on old GM alternators (with wiring diagrams). The site also includes a really thorough discussion on how the old voltage regulators work, and the best placement for that voltage sense wire.

    It won't help much with the 2 battery question, but it will make the existing system a lot more easy to understand!

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    DaveSmed's Avatar
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    Re: Second Battery?

    All you need is one wire out of the regulator harness with the new alternator. if you just want to keep the stock plug, you can use a plain male quick connect, like the kind used on the BATT terminal on a GM HEI.

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    DaveSmed's Avatar
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    Re: Second Battery?

    Excellent link! MAD electrical is a great place for information.

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    Sasquatch's Avatar
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    Re: Second Battery?

    Quote Originally Posted by DaveSmed
    A 10SI 63 amp alternator that would work well on your car has AC-Delco P/N: 321-43 Or, if you go the parts counter route, get one for a '77 Pontiac Grand Prix, 350 VIN R engine, with Air COnditioning, and Heated back light (rear defogger).
    Dave, I'm going to go with the Alt. upgrade you suggested along with the MAD Electrical wiring kit. Will the alt. you suggested line up with the exsiting brackets on my 472? What parts distributor would carry the Delco P/N 321-43? Napa or Advanced? I would like to pick it up locally if possible to save on shipping. Also if I can't find it under that part number locally then ask for an alt. for the car you described above and it will work with my stock mounting brackets? Thanks alot and it's Saturday so I'm going to make some calls for availability but thought I would ask.

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    Sasquatch's Avatar
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    Re: Second Battery?

    In reading about the Delco alt.'s on the MAD electrical sight they describe different "clock" locations for the wiring plug on the alt. I'll have to check and see which will work best for me. Also I discovered a battery isolator that will bolt to the Delco alt. I've included pictures and a description. Is the 1/4 inch post for mounting the isolator they describe the one in the picture of the alt. with the red plastic ring around it? Not sure I'm going with this particular isolator or not. Although it seems it would fit the bill nicely as long as there are no clearance issues. Here's the pics and info. Although in reading the info I do not see where it "isolates" the secondary battery during ignition off periods. I think it may be just for charging two batteries. Let me know what you guys think.


    The DC-270 is designed to facilitate the installation of an additional battery on any boat or recreational vehicle to ensure that the engine will start after spending extended periods of time anchoring, trolling or camping.



    The DC-270 will work on any 12 volt DC-negative ground electrical system with alternators of up to 70 Amps output. It is specifically not recommended for use with higher output alternators. The DC-270 will mount directly on the alternator output or 'battery' post on alternators with a 1/4" or smaller diameter post. This mounting system fits Delco, Mando, Motorola, Prestolite and many other marine and automotive alternators. In addition, the DC-270 may be flat mounted for applications where insufficient clearance is available, or for use on systems without alternators, such as outboard motors.

    DC-270


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    The Ape Man's Avatar
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    Re: Second Battery?

    Your Voltage regulator will not work properly with a battery isolator unless the regulator Voltage is taken from tha battery side of the isolator. The reason for this is the Voltage drop found in the diode in the isolator. It will be in the neighborhood of .6 to .7 Volts. This may already work in the Hearse with a generator but if you switch to an alternator with internal regulator then the regulator terminal should not be simply looped back from the B+ alternator post back to the plug. It should now go to the battery. Which battery? The one that starts the car.
    You will be much better off with an alternator than the olde generator if you decide to change.

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