# Vicor Maxi DC-DC Converter with Backup Battery



## iruraz (Sep 4, 2012)

Hi All,

I purchased Vicor 's Maxi converter module which output 's maximum value can be 13.2Vdc :

http://www.digikey.com/product-detail/en/V375A12C600BL/1102-1361-ND/2850986

I intend to use it with 12Vdc lead-acid backup battery. If DC-DC converter 's output would be about 13.8-14.2Vdc , there is no problem about the design.

Now , I am confused about connection. How should I connect Vicor 's output with 12Vdc backup battery and load? As far as I know, DC-DC should hold battery voltage on charged value, it can be 12.8Vdc in this case.

Regards.


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## iruraz (Sep 4, 2012)

What do you think about this solution? 

There is a zener diode which is 12.8V and 5W.

Maximum current which is flow over Rs resistor:

Max. Cur = 5W/12.8V = 0.39A --> ~400mA

Minimum value for Rs:

Min. Rs = (13.2V - 12.8V) / 0.4A = 1 ohm

power dissipation for Rs:

P = (0.4A) x (0.4V) = 0,16W

In this case auxiliary (backup) battery behaves like a load until it charges. It charges between 0-400mA at 12.8V. I know it is very slow charging but time is not important for me in this application. 

I would like to know your advices.

Regards.


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## bwjunkie (Jul 31, 2013)

They do sell a "evaluation only" PCB which I purchased to get an idea for the externals needed. Here is a random link to the documentation for the Vicor product #24644 in case it helps (I haven't yet powered mine up)

http://www1.futureelectronics.com/doc/VICOR CORPORATION/24644R.pdf

-josh


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## iruraz (Sep 4, 2012)

bwjunkie said:


> They do sell a "evaluation only" PCB which I purchased to get an idea for the externals needed. Here is a random link to the documentation for the Vicor product #24644 in case it helps (I haven't yet powered mine up)
> 
> http://www1.futureelectronics.com/doc/VICOR CORPORATION/24644R.pdf
> 
> -josh


Hi,

I built my evaluation board for my converter according to Vicor 's reference document which 's link above.

My main problem is about its output. Its maximum value is 13.2Vdc and it is not enough for flow voltage.

Regards


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## Tesseract (Sep 27, 2008)

iruraz said:


> I built my evaluation board for my converter according to Vicor 's reference document which 's link above.
> 
> My main problem is about its output. Its maximum value is 13.2Vdc and it is not enough for flow voltage.


No, your main problem is that you didn't read the datasheet before you bought the module, wherein it states that the output range for this series is adjustable from 10% to 110% of nominal (e.g. - 1.2V to 13.2V for 12V nominal, or 1.5V to 16.5V for 15V nominal, etc.).

So you should have bought the 15V version instead and adjusted it down to the usual 13.8V float voltage.

I sure hope you bought that module used/surplus otherwise this was a pricey mistake.


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## bwjunkie (Jul 31, 2013)

Tesseract said:


> I sure hope you bought that module used/surplus otherwise this was a pricey mistake.


Pricey for you maybe, not for some of us. 

I too was confused by the decision of which model to buy, someone told me the 15v would work with trimming, but I think I lost the unit in a box in my storage unit... still looking 

-josh


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## madderscience (Jun 28, 2008)

I'm using the  (Vicor V375A15C600BL) or the 15V, 600w nominal version as my main DC/DC and the 300W version as a secondary one that powers always-on loads like my onboard computer directly from the traction pack. I do have mine tuned for 13.8V output nominally but If I ever need to take the DC/DC apart I am going to bump it up to 14v as it doesn't quite fully charge my (18ah AGM) battery if all the load in the car are turned on. Nothing has gone dead, but the battery is usually sitting at 12.6 or 12.7 when the car is parked, that is a little low.

My website has more details of my DC/DC build at http://amphibike.org/blog/scion-xb-ev/scion-xb-ev-construction/scion-xb-ev-dcdc-converter/

These modules work well but are a bit fragile and expensive, a touchy combination for DIYers. I fried my first one during testing, $$$ please. Once behind appropriate protective circuitry they seem reliable enough. Make sure to include an input surge limiter like the CL-60 and filter capacitors, polarity protection on the input side and I also used one of the modular EMI filters from a computer power supply on the input side to help keep noise from the inverter out of it.

Ebay frequently has the more common ones available for good prices, but the high voltage/high amp ones are a little harder to come by.


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## iruraz (Sep 4, 2012)

@Tesseract,

You are right about datasheet. I should have read datasheet before buying.



> I think I lost the unit in a box in my storage unit... still looking


@bwjunkie,

Your problem is bigger than me 



> These modules work well but are a bit fragile and expensive, a touchy combination for DIYers. I fried my first one during testing, $$$ please. Once behind appropriate protective circuitry they seem reliable enough. Make sure to include an input surge limiter like the CL-60 and filter capacitors, polarity protection on the input side and I also used one of the modular EMI filters from a computer power supply on the input side to help keep noise from the inverter out of it.


@madderscience,

Thanks for your advices. I have fuse input of the module but I should add surge cuurent limiter and EMI filter as you mentioned. I have only 4.7nF bypass capacitors at input and output as reference evaluation board:

http://www.vicorpower.com/documents/user_guides/brick/UG_Maxi_MiniElvBrd.pdf

I am confused about whether continue with Vicor module (new one with 15V output) or not. It has advantages sucha as lightess and smallness. 

Other option is Chennic 's DC-DC. I have read good things about their DC-DC converter. I may purchase one of them (1200W):

http://www.chennic.com/show-products.asp?id=117&JCDI85


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## madderscience (Jun 28, 2008)

By the time you add an appropriate heat sink and all the care and feeding stuff you will probably end up with a box physically sized similarly to the chennic unit, which likely contains a couple of similar converter modules within, just as my original Solectria DC750 unit contained 4 older 200W vicor units in parallel, which I replaced with a single 600W unit.

I don't know chennic's reputation/quality but if you want off the shelf DC/DC converters aren't that expensive (I could have bought a new one for a similar price as to what I spent building mine, especially considering I fried the first vicor module) so that isn't a bad way to go. 

Despite the extra work I wanted to reuse the DC750 housing for looks and because I could get the high voltage switching relay inside along with all the care and feeding components so it made for a nice clean install.

I see the evaluation boards have electrolytic caps on their input side. I would avoid using electrolytic capacitors on the high voltage side if you build your own, at least with the Solectria units those are a known failure point though those units harken from the days of the height of the capacitor plague (see wikipedia). (both solectria DC750 units I have had blown electrolytic filter caps on the input side despite the surge limiter, meaning the temperature and voltage got to them) It is worth noting that the solectria units while claiming ratings for up to 350v were using 300V rated vicor modules with 12v nominal outputs tuned up to 13.2v, their max. So they pushed the ratings on the original design, undoubtedly to keep cost down. I went for a higher rated module (375v nominal in, 15v nominal out) and run it at lower input and output.


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## iruraz (Sep 4, 2012)

> By the time you add an appropriate heat sink and all the care and feeding stuff you will probably end up with a box physically sized similarly to the chennic unit, which likely contains a couple of similar converter modules within, just as my original Solectria DC750 unit contained 4 older 200W vicor units in parallel, which I replaced with a single 600W unit.


@madderscience,

Yes I add appropriate heat sink. I don 't think so that Chennic contains within itself DC-DC modules such as Solectria. If there are modules inside Chennic, it should be more expensive. Its price is about 400-500USD.



> I see the evaluation boards have electrolytic caps on their input side. I would avoid using electrolytic capacitors on the high voltage side if you build your own, at least with the Solectria units those are a known failure point though those units harken from the days of the height of the capacitor plague (see wikipedia). (both solectria DC750 units I have had blown electrolytic filter caps on the input side despite the surge limiter, meaning the temperature and voltage got to them)


Thanks for your advice. Capacitor plague is interesting issue:

http://en.wikipedia.org/wiki/Capacitor_plague

Solectria may has problems about input capacitor. If it is not appropriate why does Vicor use input electrolytic capacitor in their reference design?



> It is worth noting that the solectria units while claiming ratings for up to 350v were using 300V rated vicor modules with 12v nominal outputs tuned up to 13.2v, their max. So they pushed the ratings on the original design, undoubtedly to keep cost down. I went for a higher rated module (375v nominal in, 15v nominal out) and run it at lower input and output.


Aren't Solectria 's specifactions true? If their nominal output is about 13.2V, it can caues some problems for some users who operate it with auxiliary battery. Did you use their 13.2V ouput with auxiliary (backup) battery before changing with 15V ouput one?

Regards.


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