# Dc Dc converter best set up?



## TTmartin (Feb 7, 2012)

Hi all,
As usual I'm looking for advice from those that can give it
I'm converting a Audi tt in the uk, to date, I've purchased Kostov 11" 192volt and installed in car after removing a total of 350kg of parts not required for the EV, adaptor plate made along with motor to transmission coupling, soliton 1, hopefully about to be ordered.
I'm now looking at, what is the best dc to dc converter set up for this project, some people use a stand alone battery others have converters and a battery or indeed two dc to dc converters in parallel. So I would like to be put in the right direction as regards what is the best set up, I assume one DC to DC converter capable of supplying the cars needs eg, power steering, vacuum pump etc etc should be the way to go with no extra battery or am I wrong.
Is there an advantage using a battery as well like power to certain things when main pack is not in use?
Guidance please.


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## Ziggythewiz (May 16, 2010)

You seem familiar with a number of the options.

Obviously, the way I did it is the best. You should do the same.

Seriously, it depends on your needs. Figure out which way will work best for your needs. The advantage of a battery is you'll have headlights and wipers when your DC-DC goes out on the way home in that storm...or you can just skip it.


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## Tesseract (Sep 27, 2008)

TTmartin said:


> ...
> Is there an advantage using a battery as well like power to certain things when main pack is not in use?
> ...


You should always use a battery for the 12V system otherwise you are going to entrust the reliability of your EV to what is frequently the most cheaply built, ill-suited component - the dc/dc converter.

A battery will smooth out spikes and dips in the 12V supply, which will help prevent your controller from faulting every time you turn on the headlights or the windshield wipers. It will also let you run the hazard flashers should you break down. I can almost see running a car with just a battery and charging it at the same time the main pack is charged, but I can't see relying on just a dc/dc converter.

Besides, you don't have to keep the original flooded lead-acid starting battery - swap it out with a smaller/lighter gel cell battery, like the kind used for backup lights and small UPS. Something in the 7Ah to 24Ah range should work well.


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## TTmartin (Feb 7, 2012)

Quote,
Besides, you don't have to keep the original flooded lead-acid starting battery - swap it out with a smaller/lighter gel cell battery, like the kind used for backup lights and small UPS. Something in the 7Ah to 24Ah range should work well.

Thanks for response,
makes sense but just to be clear, basically the battery is doing all the work, lights, power steering etc and the DC/DC converter is acting as an altenater charging the battery from the main pack. have I got it?
If I'm right that means the DC/DC converter ideally needs to be of a spec just to keep the battery charged?You can tell I'm new to this
Sorry I'm known for asking stupid questions, I call it thinking out loud


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## Ziggythewiz (May 16, 2010)

Typically the DC-DC is doing all the work, the battery is just there to smooth it out when things turn on and in case the DC-DC fails. Just like in a regular car, the ACC batt would stay nearly fully charged at all times.


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## somanywelps (Jan 25, 2012)

Also be sure to document your conversion, the TT is an ideal candidate.


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## TTmartin (Feb 7, 2012)

Ziggythewiz said:


> Typically the DC-DC is doing all the work, the battery is just there to smooth it out when things turn on and in case the DC-DC fails. Just like in a regular car, the ACC batt would stay nearly fully charged at all times.


Thank you,
this makes total sense now my confusion came due to a lot of the conversions out there seem to have quite small DC-DC, eg 55amp output, if your running with power steering, 12v heating etc I think a larger output is required, can anyone point me in the right direction to a good manufacturer for dc-dc converter to go from around 200v to 12+ with enough output. I think the Iota 55 is to small and seems not to have a good name for EV's although it's the most used, from what I can see.


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## TTmartin (Feb 7, 2012)

somanywelps said:


> Also be sure to document your conversion, the TT is an ideal candidate.


Ok will do soon


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## Tesseract (Sep 27, 2008)

TTmartin said:


> ...a lot of the conversions out there seem to have quite small DC-DC, eg 55amp output, if your running with power steering, 12v heating etc I think a larger output is required, can anyone point me in the right direction to a good manufacturer for dc-dc converter to go from around 200v to 12+ with enough output.....


55A is actually on the high end of the output amperage for dc/dc converters in EVs.. if you think you need more than that then I hope you are prepared to pay big money. 200V is an awkward voltage, too, as it is in between the two most common AC voltages used in the world (115VAC and 230VAC) and most of the DC/DC converters on the market are just repurposed switching power supplies (e.g., the IOTA).

The only converter I can think of that comes close to what you want - more than 55A output and *might* operate on 200V - is Delphi's monster 2.2kW unit available from New Eagle. IIRC, the price is around $950 (you have to sign up on their site to see the prices).

It might be a smart idea to put a peak-holding clamp DC ammeter on the cable from the alternator to the battery to see how much current you are actually pulling from the alternator. You might find out that 40-50A is all you really need, along with a small 12V battery to smooth out the bumps along the way. Could save you $500-$700.


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## Ziggythewiz (May 16, 2010)

You should really test your system to see how much you need. Mine pulls under 15 A with everything on. Unlike your motor/controller, you can test anything about the 12V system while stationary.


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## TTmartin (Feb 7, 2012)

Quote,
It might be a smart idea to put a peak-holding clamp DC ammeter on the cable from the alternator to the battery to see how much current you are actually pulling from the alternator. You might find out that 40-50A is all you really need, along with a small 12V battery to smooth out the bumps along the way. 

Quote,
Re: Dc Dc converter best set up?
You should really test your system to see how much you need. Mine pulls under 15 A with everything on. Unlike your motor/controller, you can test anything about the 12V system while stationary.

Ok guys, humor me I think I'm nearly there,

Unfortunately I can't put an amp clamp on to test system yet, to many things hanging loose power steering plumbed in on the hydraulics but not wired in yet.
Also planning on using 12 v water heater element designed for solar power not sourced yet. 
But I think your saying even with the big amp draw components eg, power steering peaking at possibly 75amps the dc-dc converter at 55amps will cope most of the time with the battery taking care of the extra current when the heater or steering etc kick in, then at lower demand times dc-dc tops up battery


__________________
1 EV - 5,000 e-miles - http://www.evalbum.com/4000


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## Ziggythewiz (May 16, 2010)

Yes, you hopefully would not be averaging more than that. I average ~2.5, manual everything is great!


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## Yukon_Shane (Jul 15, 2010)

TTmartin said:


> ...Also planning on using 12 v water heater element designed for solar power not sourced yet...


I'm assuming that you would be hoping to use this 12v heater for cab heat in which case I might suggest doing a bit of search on the forum for previous discussion on this topic.

I don't know the specifics of the 12V product is that your looking at for heating but my sense is that it would be difficult to supply sufficient cab heat with a 12 V heating element. Most DIY EV's use atleast 1500 watt heaters for cab heat and these are typically reported to be undersized.

It's likely better to use the pack voltage for heating and avoid the need for an unnecessarily large DC/DC.

It's also worth noting that Evnetics is working on a DC/DC converter that will handle your proposed pack voltage with ease. 

Tesseract is likely not mentioning his work on this out of respect for the forum rules but I think it's relevant to this discussion.


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## Joey (Oct 12, 2007)

Yukon_Shane said:


> It's also worth noting that Evnetics is working on a DC/DC converter that will handle your proposed pack voltage with ease.


I hope this is true. I'd be willing to buy one now for delivery in 6-12 months (I still have a ways to go on my conversion). There is a big hole in the market for a quality DC-DC converter.


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## jehan12413 (Feb 4, 2010)

TTmartin said:


> Thank you,
> this makes total sense now my confusion came due to a lot of the conversions out there seem to have quite small DC-DC, eg 55amp output, if your running with power steering, 12v heating etc I think a larger output is required, can anyone point me in the right direction to a good manufacturer for dc-dc converter to go from around 200v to 12+ with enough output. I think the Iota 55 is to small and seems not to have a good name for EV's although it's the most used, from what I can see.


 You might want to search ebay for VICOR VI-251-09 bricks. They are available from time to time for a decent price. The 09 has an input voltage range of 150-250v and they are easy to parallel. I currently use three for about 44A output. It seems many people aren't too fond of VICOR but I haven't had any problems.


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## Tesseract (Sep 27, 2008)

Yeah, using 12V for heating is just plain crazy. If you find you need 100A+ of 12V in your EV then you are doing something wrong. Probably something like using a 12V cabin heater! 

And yes, the rumors are true - I got tired of hearing complaints from Rebirth Auto about how crappy it is to use an off-the-shelf switchmode power supply (SMPS) as a dc/dc converter. My dc/dc is going to be significantly more expensive than a plain old SMPS mainly because it will be designed for the harsh environment of an on-road vehicle - a die-cast sealed aluminum box, at least a 4:1 input voltage range (max of 425V - same as a Shiva), easily paralleled, highly abuse resistant, etc... I won't know for sure how much output current I can get out of the available enclosure sizes, transformer cores, semiconductors, etc, until I build a prototype, but it will be in the range of 30-50A at a fixed voltage of 14.0V. Depending on the connector(s) - if any - used for the wiring I might also include remote sense (to compensate for voltage drops in the wiring) and remote shutdown (to physically disconnect the converter from the traction pack when the car is off).

Finding a suitable connector - especially for the high current 12V side - is often the hardest part in designing an electronic product. Most EEs will agree that all connectors suck in one way or another. I want our dc/dc to at least be splash-proof, like our controllers, so that eliminates a lot of the "low hanging fruit" in connector selection.

Finally, the Vicor modules are good products, but also not designed for the EV environment. You should add a ripple filter ahead of the DC input, a heatsink for the modules to bolt onto, and you have to solder the wiring to "staked pins" yourself. They are more in the "rolling science project" category of solutions, rather than a polished product, but using them is perfectly reasonable for technically-savvy DIYers. Conversion shops can't exactly rely on the supply of surplus modules on eBay, however, as these Vicors are not cheap when purchased brand new.


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## PStechPaul (May 1, 2012)

I just joined your forum and I would like to add some of my expertise and experience with DC-DC converters and other components that are useful for EVs. I have installed a 240/480 V, 2 HP 3-phase induction motor on a stripped-down riding mower, and I built a DC-DC converter which takes 12 VDC from a small SLA battery and provides 320 VDC for the DC link of a standard VF motor controller. In its final form, it should be able to provide 1500 watts, or 2 HP, from two or three batteries in series (24 or 36 volts). The same design can be upgraded to higher power and voltage, or multiple units could be connected in series or parallel for the power needed.

I was able to build this using surplus and junk power components, and a few simple items like a Microchip PIC. So it really cost almost nothing except my time designing and building it. If it works well enough, I may enhance the design and put the circuitry on PC boards to simplify assembly. I think this can be built for something like $50/kW, even using new components. If you are interested, I'd be happy to assist you in building a similar unit. Here is a video showing my first ride using these components:

http://youtu.be/y0qWY4bVnEA

See my introductory post for other details.


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## mcbrems (Oct 28, 2011)

Does anybody have any good suggestions for a compact 12 volt gel battery mentioned above? Not much room to work with, as I didn't expect to be using a 12v cell. Brand, model?

Thanks,
McB
http://www.evalbum.com/3576


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## EVfun (Mar 14, 2010)

This is the size I use. I like to use a 12 volt AGM battery with a capacity of around 20 amp hours. This is the size used in the old Zappy scooters.


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## aeroscott (Jan 5, 2008)

PStechPaul said:


> I just joined your forum and I would like to add some of my expertise and experience with DC-DC converters and other components that are useful for EVs. I have installed a 240/480 V, 2 HP 3-phase induction motor on a stripped-down riding mower, and I built a DC-DC converter which takes 12 VDC from a small SLA battery and provides 320 VDC for the DC link of a standard VF motor controller. In its final form, it should be able to provide 1500 watts, or 2 HP, from two or three batteries in series (24 or 36 volts). The same design can be upgraded to higher power and voltage, or multiple units could be connected in series or parallel for the power needed.
> 
> I was able to build this using surplus and junk power components, and a few simple items like a Microchip PIC. So it really cost almost nothing except my time designing and building it. If it works well enough, I may enhance the design and put the circuitry on PC boards to simplify assembly. I think this can be built for something like $50/kW, even using new components. If you are interested, I'd be happy to assist you in building a similar unit. Here is a video showing my first ride using these components:
> 
> ...


great work I need some water pumps etc.


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## Tesseract (Sep 27, 2008)

PStechPaul said:


> ... I think this can be built for something like $50/kW, even using new components. ....


Guess I don't need to bother making one myself, then. Just the box I picked cost $50 so no way I can compete with you. Let me know when you have some ready to sell and we'll give them a right and proper torture testing with our dyno battery pack.


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## TTmartin (Feb 7, 2012)

> Chief electron herder
> 
> Thankyou for your, (to the point) input on this subject.
> I now know alot more than I did on the subject, thats what I was after. Ok the 12v heater is maybe a dumb idea, I'm learning
> ...


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## PStechPaul (May 1, 2012)

TTmartin said:


> > Chief electron herder
> >
> > Thankyou for your, (to the point) input on this subject.
> > I now know alot more than I did on the subject, thats what I was after. Ok the 12v heater is maybe a dumb idea, I'm learning
> ...


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## PStechPaul (May 1, 2012)

Tesseract said:


> Guess I don't need to bother making one myself, then. Just the box I picked cost $50 so no way I can compete with you. Let me know when you have some ready to sell and we'll give them a right and proper torture testing with our dyno battery pack.


I was amazed at the relatively low cost of the Soliton motor controllers on the Evnetics web site - about $10/kW. But I don't know much about brush motor controllers, except tiny ones for toy motors in slot cars and such. I would assume that these controllers are basically high current PWM devices, probably using MOSFETs or IGBTs. I have some large IGBTs that I bought surplus/used on eBay, and the smallest Soliton Jr would probably require four large units like these 400A 1200V modules which are available for $100:
http://www.ebay.com/itm/4-Toshiba-M...619?pt=LH_DefaultDomain_0&hash=item2ebbf12cab

Similar modules are about $160 each, list price, from DigiKey. 1000 amp 600 V modules are non-stock, but are available for about the same price in quantities of 10. So I suppose it is possible to make a PWM module such as this for under $1000 and sell for $2000.

A 150 HP (112 kW) three phase motor controller, OTOH, sells for about $13,000 new on eBay:
http://www.ebay.com/itm/150-HP-M141...703?pt=LH_DefaultDomain_0&hash=item519cb2602f

The DC brush motor PWM controller is probably much less complex, but once the control circuitry has been designed, it is probably simple to scale up from something like the 2 HP unit I got for under $100. So I'm just trying to get a handle on the relative sizes and costs for the two different technologies. 

I do question, however, the need for a 150 kW motor in a passenger EV, much less 300 kW and the 1.2 MW Shiva I saw. I have understood that an electric motor of about 30 HP is more than equivalent to a 100 HP ICE, so I'm wondering what sort of vehicles these are used in. I'm a relative newbie to electric cars, and have no direct experience, so maybe I'm missing something?


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## hbthink (Dec 21, 2010)

Do folks leave their DC/DC connected at all times so that 12v is always available? Or do they use a contactor to turn it off? and if off does the 12v auxilary battery still provide 12v?

I was going to use a TDK Lambda LS-200-12 which provides 16.7 amps at 12v and back it up with a 12.8v lithium cell at 20ah rated. The car is a VW Rabbit convertible mostly LED lights, power brakes and headlights, I doubt my average is over 4-5 amps total, mostly the headlights.

Elithion has a good whitepaper that uses a relay powered by a 1F capacitor (big!) to turn the DC-DC on and off.

http://liionbms.com/php/wp_ignition_conundrum.php

seems a bit overkill but should work. 

Steve


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## PStechPaul (May 1, 2012)

If you want to duplicate this circuit, you can get 5F 2.7V capacitors from Newark for $2.36 each: http://www.newark.com/illinois-capacitor/505dcn2r7q/supercapacitor-alum-elect-5f-2/dp/02P5131

So 5 in series gives you 1F at 13.5V. You may need a voltage divider or a string of 2.5V zeners to balance the voltages. LEDs might be used instead of zeners. Either way, they won't discharge the caps below their threshold voltages. But why not just use a small 12V battery pack?

It may not be commonly known, but an ordinary 12 VDC switching supply can work on an input of 85 to 264 VAC, or 120 to 370 VDC. A 12.5 amp supply is about $100:
http://www.newark.com/iccnexergy/fsa150012a/switch-mode-power-supply/dp/51R1797

But you can get a 12V 17A supply from Marlin P Jones, for about $15:
http://www.mpja.com/12V-17A-Phihong-Power-Supply/productinfo/18091+PS/

I might not be understanding the problem, but maybe there is a reason for using the main battery pack for all of the vehicle power requirements, and not a separate 12VDC battery for accessories and control circuitry. If it should fail, it would be simple to use an ordinary 12 VDC jump starter, or even just a small source of 12 VDC such as a flashlight. And there are circuits that can boost as little as 1.5 VDC to 12 VDC for the control circuitry, at least enough to actuate the main relay for the HV.


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## coulombKid (Jan 10, 2009)

If I'm scratch building and opt for, say, an auxiliary 18 volt lithium prismatic battery pack sized to drive a passive regulator, wouldn't that be cheaper and more efficient? Putting a 120VAC/60 hZ inverter on board? I get that. I can use so many common cheap devices (vacuum pumps, hydraulic pumps, AC compressors). I don't get the fixation on a Pack voltage to 12 VDC system. No doubt a 18 volt pack has to outlast the traction pack on charge but it should be cheaper and lighter over all from any angle. The catch is sourcing a second lower voltage charger. Tesseract admits the reliability record of the DC-DC converters is abysmal. The second lower voltage pack would extend the range of the traction pack two ways. The energy not used in a buck conversion and the energy used directly from the 18 volt source. You have to carry enough lithium either way if the conversion was 100% but we know it cannot be.


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## mcbrems (Oct 28, 2011)

In many cases, the DC/DC converter is a dual-purposed 14 volt charger.


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## aeroscott (Jan 5, 2008)

I found at the junk yard a hot swappable( I think) power supply from a server or similar . 12" X 3" X1.5" , 12.2 v @48a , 5 Vco @.2a=585watts total max. it has dc input( on label) of 140-224v @ 5.5a as well as the ac input , 100-127v 50/60 hz @8.3A , 200-240 50/60hz,4.0A , AcBel,TUV, RU us , IBM P/N 24R2639 ,FRU P/N 24R2640 , warning this is a class A product . in a domestic environment this product may cause radio interference . So if a large number of these or similar ones could be found we could have a server/ commercial grade DC to DC , AC to DC charger and if cheap, a backup/hot swappable unit.


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## Ziggythewiz (May 16, 2010)

The main issue with a server supply would be the vibrations. They're not designed to move, and also like lots of AC. It they're cheap though, certainly worth a try.


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## aeroscott (Jan 5, 2008)

they are cheap $20-40 , think it needs a controller . probably should be mounted on soft mounts , good for all the electronics even if designed for tough environments .


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