# Alternator vs DC-DC Converter



## Greenflight (Sep 13, 2007)

Well, in my opinion, no. It would more or less eliminate the need for a DC/DC, but you'd also have to use a 12V aux battery. The complexity of coupling the alternator to the motor shaft in many cases outweighs the benefits. Not to mention when the car is sitting still and the motor isn't idling, you're not putting out power.

There are a few people who have done this, and are happy with the results, so you never know.  

If you're looking to save some $$, at least in the short term, you could do like I'm doing and use a marine deep cycle 12v aux battery with a $30 charger hardwired to the main charge plug. The deep cycle battery can handle running the lights etc. on just about any local trip. It works, it just loses some of the "common sense" value of a DC/DC. The downside is that if you ever decide to upgrade to a DC/DC you've wasted your money on a cheap charger and big battery.

Good luck!


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## Xanerrix (Sep 25, 2007)

that's a great idea... never thought of it before.
but I suppose it might be more advantageous to have an extra battery in the bank instead of having a large aux battery.
One question though, does having a DC/DC eliminate the need for an aux battery altogether? Oh and how much does one cost normally?

Thanks
Andre


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## Nick Smith (Oct 26, 2007)

You can get away without a battery if you correctly size your DC/DC for the maximum power draw you require for all 12V loads including lights, radio, horn everything. If the DC/DC is oversized it doesn't matter as it will only provide as much power as required at the time. You will need to pay attention to how you wire it in as there will be no 12v power at all until the DC/DC is actually going and hence you may not be able to activate any contactors, solenoids, or relays.

Most donors will already have a starting battery anyway so i would recommend leaving it in. The battery acts as a reservoir for those intermittent high current draw situations so you can get away with a smaller (and cheaper) DC/DC. You could always swap it out for a smaller, inexpensive, deep cycle battery as the starting requirement is no longer needed. I have not checked my actual requirements but I assumed that 45A would be enough while retaining the battery.

You should *not* take 12v auxilliary power from one of the traction pack batteries. Apart from the obvious risk of grounding the traction pack to the car body, this will also preferentially draw down on the battery and cause early death with regards to the rest of the pack. A separate 12V battery (isolated from the traction pack) is also quite workable. There is a possibility of the aux. battery becoming drained before you get where you need to be - no lights, no wipers...  I think the DC/DC is far less hassle and it means you always have 12V as long as the pack has charge.

As far as cost goes - I did a _really_ quick search on the one I am using and came up with this for only $175: http://www.rvupgradestore.com/index.asp?PageAction=VIEWPROD&ProdID=411

You could probably get it a little cheaper if you shopped around - this was the first retail site I turned up on google.


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## John (Sep 11, 2007)

I have one of those also. I found this site after I'd already bought it. http://store.solar-electric.com/bach1.html I was looking for an IQ4 controller for it. I'm not sure wether or not an IQ4 controller would be beneficial in an EV.


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