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Old 07-23-2009, 05:44 PM   #141 (permalink)
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Wouldn't a voltage doubler be cheaper than a PFC?

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Old 07-23-2009, 08:41 PM   #142 (permalink)
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Quote:
Originally Posted by NiHaoMike View Post
Wouldn't a voltage doubler be cheaper than a PFC?
I don't know for sure. I've seen 5kw stepup transformers on ebay for 70 bucks or so, and it's a 7" block of iron that weighs like 30 lbs. I've seen the schematics for the capacitor method, but I don't know how well it works at high power or how efficient it is.

this is a pdf for a pfc IC
http://www.irf.com/product-info/data...ata/ir1150.pdf

I haven't really looked into using it, but it seems that the most expensive parts would be the mosfet and inductor and maybe some ripple caps, but otherwise the circuit doesn't look too crazy. let's say it adds up to the price of a stepup transformer, or maybe it's $50 more - you'd get the added benefit of lower weight and active PFC for roughly the same price or a little more. maybe it's worth it? active pfc is a ton more complicated compared to a transformer or cap.

It'd be interesting to measure what the powerfactor currently is - maybe it's not that bad? I don't have the proper tools...
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Old 07-23-2009, 10:21 PM   #143 (permalink)
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A capacitive voltage doubler is more efficient than either PFC or a step up transformer.
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Old 07-24-2009, 07:56 PM   #144 (permalink)
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Quote:
Originally Posted by NiHaoMike View Post
A capacitive voltage doubler is more efficient than either PFC or a step up transformer.
Cool! Are there guidelines for high power designs? In my brief search of the web, I couldn't find any details...
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Old 07-24-2009, 10:50 PM   #145 (permalink)
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Very nice work! This makes me really enthusiastic!

It also makes me a bit concerned about safety. This charger isn't isolated from the grid, right? Doesn't that mean the cars chassis will be connected to the grid when charging? (assuming one of the battery poles are connected to the chassis) That could be dangerous.
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Old 07-24-2009, 11:25 PM   #146 (permalink)
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The batteries should be isolated from the car chassis and the chassis should be grounded.

If isolation is needed, a full bridge design can be used, but it is much more complex and more expensive.
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Old 07-24-2009, 11:40 PM   #147 (permalink)
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That means everything connected to the battery has to be isolated, or the battery has to be disconnected while charging. Well, hm, I guess it would be pretty easy to make something that disconnects the battery while charging.
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Old 07-25-2009, 12:28 AM   #148 (permalink)
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usually there's a contactor that keeps the circuit open. Then you just have a big battery pack just sitting there, isolated. It's not really a hassle. Then you just charge the isolated pack. No problem! The controller, motor, etc. is not a part of the loop because of the contactor.
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Old 07-25-2009, 02:09 AM   #149 (permalink)
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Ah, you are using two contactors?
I had planned to use only one on my build.

The contactors should be able to isolate grid voltage then, which they probably aren't made for, but may do.

Used with a ground fault circuit interrupter the charger should be pretty safe even if something bad happens, like arcs jumping in the contactors.
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Old 07-25-2009, 08:31 PM   #150 (permalink)
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Quote:
Originally Posted by bjn View Post
Ah, you are using two contactors?
I had planned to use only one on my build.

The contactors should be able to isolate grid voltage then, which they probably aren't made for, but may do.

Used with a ground fault circuit interrupter the charger should be pretty safe even if something bad happens, like arcs jumping in the contactors.
The contactors should not arc if they're sized right and switched at zero current. (Which means stop the motor before disconnecting and precharge before connecting.)

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