# Boost Converters and Transformers for Charging a 360 V Pack



## xrotaryguy (Jul 26, 2007)

I am looking at building my own charger for my EV project. My pack consists of two strings of 30 12V 17ah AGM batteries for 360V and 34ah. I can charge at a a miximum voltage of 420V a max rate of 8.0 amps. 

I have considered a couple of possibilities. One possibility is to use one or more transformers to get the required voltage and amperage. The other is to use boost converters for the same purpose. The trouble is simply that I can't find transformers or converters that can handle that kind of voltage.

Can anyone point me in the direction of a high voltage boost converter or transformer?

Thanks,


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## Tesseract (Sep 27, 2008)

xrotaryguy said:


> ...
> Can anyone point me in the direction of a high voltage boost converter or transformer?
> ...


Any switching power supply that has "active" power factor correction (PFC) will most likely (but not necessarily!) use a boost topology converter in the PFC front end. Frequently the output voltage of the PFC stage is set to 380V, but is sometimes as high as 400V. With a 220-240VAC input it would not be very taxing on the switch/inductor to raise the output to as much as 420V.

On good source for a big bad active PFC front end is in a telecom "rectifier"... aka, rack mounted 48VDC power supplies frequently in the 1-10kW range. I bought a 3kW unit about a year ago just because it was going for $99 (I specifically wanted the PFC front end, too).

Now, as a regulated power supply, a PFC front end is terrible - usually no better than 2%, and often as bad as 5% - and, of course the transient response sucks, too (the loop bandwidth has to be low because it is trying to draw sinusoidal current at the line frequency). Fortunately, a battery charger is not (normally) subject to fast changes in current demand, so this is a non-issue. You'll still have to do some hardware hacking to turn the thing into an automatic charger, but it's not what I'd call too difficult if you have a reasonable grasp of electronics (can read an IC datasheet, etc.).


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## Roy Von Rogers (Mar 21, 2009)

I cant advice you on anything that are switching supplies, I'm not knowledgeable enough on the subject. But when you mentioned transformers the first thing that came to mind was some of the transformers I aquired being in the military.

These transformers are for overseas converting 240 to 120 USA appliances. I have several of those accumulated but dont remember the wattages. But I know we ran a microwave on one. Those things are large and heavy and you may be able to find one locally. Connect 240 to the 120 side and you can get aprox 440, something to consider if you get desperate.

Also you can divide the pack and use isolated chargers to charge, as long as you have enough amps from your mains.

If you divide by 4 thats 90v each section, a bit easier to handle.

Roy


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## Tesseract (Sep 27, 2008)

Roy Von Rogers said:


> ...Connect 240 to the 120 side and you can get aprox 440, something to consider if you get desperate...


That's not such a good idea, Roy, because if you try to apply twice the rated voltage to a transformer it will try to draw twice it's rated current. "Try" is the key word here... the transformer core will either immediately saturate - even without a load - and trip a breaker, or, worse, it will tolerate it long enough to catch on fire.


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## jackbauer (Jan 12, 2008)

You could however turn it into an auto transformer though it will not then provide isolation. Another option may be to use simonrafferty's charger in boost mode:
http://www.diyelectriccar.com/forum...build-your-own-intelligent-charger-36627.html


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## Roy Von Rogers (Mar 21, 2009)

Well considering your the expert here, I stand corrected. My impression was that 1800 watts is 1800 watts, no matter wich way its hooked up, at of course a much lower amperage at 440.

Roy


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## SimonRafferty (Apr 13, 2009)

I've used this topology for boost converters before now - 
http://www.diyelectriccar.com/forums/showpost.php?p=142384&postcount=24

Generally for lower voltage, lower power - but you could swap the buck converter stage in the charger that thread is about with a boost converter pretty easily using the same software.

Si


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## xrotaryguy (Jul 26, 2007)

I was worried about using an under rated transformer as well. There are lots of 120 to 28 V transformers out there and they would certainly give me the voltage I'm looking for. Unfortunately, they are rated for no more than 110V or somewhere there abouts. I'd bu up as high as four times that. I would worry about the insulation being insufficient.

I think I would need to run too much current through it to make it run hot right? In my case, I'd be watching current on the primary (low voltage) side. I'd be able to parallel a few of them if necessary, but I still don't like running that kind of voltage through them.


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## xrotaryguy (Jul 26, 2007)

Tesseract said:


> Any switching power supply that has "active" power factor correction (PFC) will most likely (but not necessarily!) use a boost topology converter in the PFC front end. Frequently the output voltage of the PFC stage is set to 380V, but is sometimes as high as 400V. With a 220-240VAC input it would not be very taxing on the switch/inductor to raise the output to as much as 420V.
> 
> On good source for a big bad active PFC front end is in a telecom "rectifier"... aka, rack mounted 48VDC power supplies frequently in the 1-10kW range. I bought a 3kW unit about a year ago just because it was going for $99 (I specifically wanted the PFC front end, too).
> 
> Now, as a regulated power supply, a PFC front end is terrible - usually no better than 2%, and often as bad as 5% - and, of course the transient response sucks, too (the loop bandwidth has to be low because it is trying to draw sinusoidal current at the line frequency). Fortunately, a battery charger is not (normally) subject to fast changes in current demand, so this is a non-issue. You'll still have to do some hardware hacking to turn the thing into an automatic charger, but it's not what I'd call too difficult if you have a reasonable grasp of electronics (can read an IC datasheet, etc.).


A PFC front end? Are you saying that I could use the switching hardware (and software if there is any) , cap(s) and the inductor? I am assuming that the rest of this hardware in a telecom rectifier is set up to regulate the converter's output voltage back down to 48 VDC?


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## Tesseract (Sep 27, 2008)

xrotaryguy said:


> A PFC front end? Are you saying that I could use the switching hardware (and software if there is any) , cap(s) and the inductor? I am assuming that the rest of this hardware in a telecom rectifier is set up to regulate the converter's output voltage back down to 48 VDC?


You pretty much got it. Granted, it will still take quite a bit of work to go from this to a working 420VDC charger, but that's sorta what you should have expected picking such a weird and high voltage for your battery pack


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## xrotaryguy (Jul 26, 2007)

Tesseract said:


> You pretty much got it. Granted, it will still take quite a bit of work to go from this to a working 420VDC charger, but that's sorta what you should have expected picking such a weird and high voltage for your battery pack


Good news. I walked into work today to find that my boss had dropped three high-current transformers and what appears to be the scary side of a boost converter. 

By the way, for anyone that might doubt that it's very easy to kill yourself with this kind of voltage... I accidentally vaporized one of the leads on my multimeter a couple days ago. I still had it set up for checking current when testing voltage. Swish! Gone!

I have electrician's gloves on order now.


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