# 160v to 72v conversion



## Roy Von Rogers (Mar 21, 2009)

Hi all.

I need some ideas on how to convert from about 160v to 72-84v.

Here is the low down...

I have an EV thats running on 7 - 12v AGM batteries. I'm planning on converting to 48 lithium using Soliton Jr, which means somewhere at 160 volts, the EV is setup to run on 72-84 volts with ignition and relays controlling forward reverse and other items.

I dont want to convert to 12v control for obvious reasons (too many things to change)

I need a way to convert the 160v to the lower 72v so I can use the original control system. Not sure of how much amperage, but it needs to handle the dc-dc converter wich runs a small aux battery, the main and directional relays, and the lighting system.

Any good ideas are welcome, I do have some electronic experience, was thinking about using an igbt with a driver, but lack knowledge and experience with igbt's, but could build it if given a schematic.

Have been looking for ready made converter, but not having any luck finding it.


Roy


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## frodus (Apr 12, 2008)

I'd use a DC-DC converter, but most I know of convert to buss voltages like 48V and below.

Maybe Vicor, meanwell, etc could do something custom.


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## Roy Von Rogers (Mar 21, 2009)

Yea I know, thats why I asked here to see if anyone has an idea.

I looked at Vicor and they do have some with output of 72, but seem low on wattage, not enough for my needs.

Unless I missed something in Vicor's items.


Roy


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## bjfreeman (Dec 7, 2011)

your basically doing a step down which is simpler than a step up.
if you want to do something your self you can do a simple zener diode, if the power is with in limit of the zener. The problem with zener is it is a constant power draw.
you can do a Pwm and mosfet with voltage sensing.


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## Weisheimer (May 11, 2009)

Roy Von Rogers said:


> Yea I know, thats why I asked here to see if anyone has an idea.
> 
> I looked at Vicor and they do have some with output of 72, but seem low on wattage, not enough for my needs.
> 
> ...


I'm not sure what your 72v is used for other than to power the present DC-DC converter that you have now.

Do you actually use it to run a control system with 72v relays and such?

If you are REALLY needing to keep the 72vdc system for that, then possibly one of the Vicor MegaPac units would suite you.
It is a modular unit that has plug in cards that provide the needed output voltage and current.
The common surplus units can supply quite a load, but you might have to get several of them to get all of the modules that you need.

As an example, here is a unit that can hold 8 modules.
It comes with a 70 vdc 2.8 amp module and other modules including a 5vdc 40 amp module.
If you got three of these power supplies, you could mix and match modules using 3 of the 70 vdc 2.8 amp modules wired them in parallel for 8.4 amps at 72vdc.
You could also put 3 of the 5vdc 40 amp modules in and wire them in series for 15vdc at 40 amps to replace your present DC-DC converter.
Each of these modules can have the voltage adjusted up or down a bit, so you can make the 15vdc be 13.8vdc or 14.1 vdc if you use AGM for your aux battery.

Here is an example:

http://www.ebay.com/itm/Vicor-MegaP...854?pt=LH_DefaultDomain_0&hash=item2c615ddec6

Here is Vicor's page on the MegaPac series, along with information about adjusting the voltage output of modules.

http://www.vicorpower.com/cms/home/products/brick/PFCMegaPAC

Tesseract suggested using a toroid inductor on the DC INPUT of the MegaPacs:

http://search.digikey.com/us/en/products/CTX100-10-52LPR/513-1720-ND/1144855


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## frodus (Apr 12, 2008)

Well, what are your requirements? It's a bit hard to go on voltage alone. How many watts? Size? sealed?



Roy Von Rogers said:


> Yea I know, thats why I asked here to see if anyone has an idea.
> 
> I looked at Vicor and they do have some with output of 72, but seem low on wattage, not enough for my needs.
> 
> ...


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## DJBecker (Nov 3, 2010)

Roy Von Rogers said:


> I have an EV thats running on 7 - 12v AGM batteries. I'm planning on converting to 48 lithium using Soliton Jr, which means somewhere at 160 volts


You might be a little under with the voltage requirement.

48 freshly charged cells may well surpass 200V. They'll drop down to 150V-160V pretty quickly once under load, but that's not what you have to design for.

You'll not find much in the way of commercial products with a 72V output. How much current do you really need to support at that voltage?


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## ishiwgao (May 5, 2011)

umm, not to act smart or anything, but is there something I'm missing? if your system runs at 72-84V, and you have 48 Li cells that make 160V, why don't u just run them in 24S2P rather than 48S1P?

The soliton jr is able to take all the way down to 8V, so it doesn't matter right? What am i missing?


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## DJBecker (Nov 3, 2010)

Presumably one reason for the upgrade was to get higher speed with good efficiency, possible only with higher voltage.


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## bjfreeman (Dec 7, 2011)

Weisheimer said:


> http://www.ebay.com/itm/Vicor-MegaP...854?pt=LH_DefaultDomain_0&hash=item2c615ddec6
> 
> http://www.vicorpower.com/cms/home/products/brick/PFCMegaPAC
> 
> ...


both of these have 115/230 VAC 15A 47-500Hz input not sure how you would hook 160 DC into it.


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## major (Apr 4, 2008)

bjfreeman said:


> both of these have 115/230 VAC 15A 47-500Hz input not sure how you would hook DC into it.


The MegaPAC spec reads: 




> Universal Input:
> 
> 85-264 Vac
> 47-500 Hz
> 100-380 Vdc


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