# DC/DC converter installation confusion



## Frankencar (Nov 17, 2008)

Hi all. Well after my last post I was definitely convinced that the dc/dc converter along with small 12v aux battery was the right way to go. One question though: I don't know how an alternator is wired, so I'm wondering how the dc/dc wiring works? Should it just be wired right to the posts of the aux battery? Also, looking at some wiring diagrams in my books, I don't see how the power is actually reaching the dc/dc converter to begin with. It looks like an isolated system.


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## madderscience (Jun 28, 2008)

The basic DC/DC should have 4 terminals. 2 of these are the input side, and will go straight across your traction battery. (with a fuse, of course ). The output side goes straight to the terminals of your 12V battery (also with an appropriately sized fuse , of course) 

The DC/DC must be isolated (no direct electrical connection between the high voltage side and the low voltage side). This is because the traction circuit of the car must be isolated from the chassis for safety, and the 12V system of the car uses the chassis for ground)

Any DC/DC you buy from an EV parts retailer should be isolated, but some golf cart and equipment DC/DC converters aren't so be careful if you go that route. make sure and buy a DC/DC that is designed for the right input voltage (they usually work over a range of input voltages) and that the output voltage is correct to charge a 12V battery (usually about 13.6V)

I am using an Intelipower 9160 RV battery charger. It is inexpensive compared to many DC/DC options and it works well, except that it should really have a nominal battery voltage of 144v to 192v or so. Its output sags a bit when my 126V battery is under a lot of load, like when accelerating hard. The only downside to it is that it is not a sealed unit, so it must be mounted someplace dry.


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## dataman19 (Oct 7, 2009)

Madderscience...
4-wire alternator?
What make and model does this apply to?
..
Newer GM Delco Alternators are two-wire.
They have a lead for the common (ground) and a terminal that hooks up to the battery.
..
The newer alternators have a triode (three-diode) assembly inside the alternator that interconnects the "three" field windings into one output.
The Alternators stator winding (the one that is energized to supply the reference electromagnetic field - necessary to generate an electrical field in the field coil( is controlled by an internal regulator. This internal regulator determines the alternators output (ie: the 13.8VDC required to charge and keep the battery charged, and maintains the voltage throughout the rrated curent range of the alternator).
..
The older (pre 70's) alternators use the old 4-wire. This used an external regulator (comprised of a bi-metal contact in older models - like 1940', and an electronic module - used in chryslers throughout the 70's).
..
If you have an alternator with 4-pins - you have an externally excited/regulated alternator. An alternator with one (actually two when you consider the alternator case is ground - the second lead) or two leads/terminals - you have an internally excited/regulated alternator.
..
The older 4-lead alternators were and still are the favoraties for the wind generators. Because they can be modified to generate up to 180 VAC.
..
Just food for thought (no bad intentions - I apologize in advance if offense taken)..
Dave Mason
dataman19


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## madderscience (Jun 28, 2008)

I was not talking about alternators, I was talking about how you select and install a typical DC/DC converter. You do not need an alternator in an EV conversion, the DC/DC replaces it completely.


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## dataman19 (Oct 7, 2009)

But Madderscience,
Frankencar asked the question:
>>"I don't know how an alternator is wired, so I'm wondering how the dc/dc >>wiring works? Should it just be wired right to the posts of the aux >>battery?"
..
Your response did not address the alternator wiring.
If he subs the factory wiring for the alternator to wire in his "DC/DC" Converter he will be confused by all the blowing fuses.
..
My caution is to verify the alternator wiring (be it internal or external regulated) and make sure that all the "alternator circuitry (including external voltage reguklators, like may chrylers) is taken out to eliminate interaction.
..
Just because a person cuts the Red lead from Alternator to battery does not mean they have taken the alternator circuit out.
..
Dave Mason
aka: dataman19


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## dtbaker (Jan 5, 2008)

Frankencar said:


> Hi all. Well after my last post I was definitely convinced that the dc/dc converter along with small 12v aux battery was the right way to go. One question though: I don't know how an alternator is wired, so I'm wondering how the dc/dc wiring works? Should it just be wired right to the posts of the aux battery? Also, looking at some wiring diagrams in my books, I don't see how the power is actually reaching the dc/dc converter to begin with. It looks like an isolated system.


If you have a dc-dc convertor you probably do not need an aux 12v battery at all.... the output from the dc-dc goes to your old 'main' 12v+ lead into the car fuseblock, and 12v- ground to chassis (where the old battery used to go). Input should be fused from your traction pack.

alternator is completely out of the picture.


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