# High power dc/dc converter?

Hi, I’m new.
Just brainstorming, about making an electric car.
Just to give my background, I’m an industrial electrical controls technician, familiar with installing & setting up 3phase AC inverter drives.

I want to (at some point) make an AC drive car.

I know from the Yaskawa drives that I most familiar with, that you can feed 600VDC to the DC common bus and get 480VAC output. I was pondering if I could find a drive with a bad rectifier section but good inverter section for a discount price, then I could make something work. The problem is, how to get 600VDC from batteries. it would take a ton of them. I have searched the net without much success for a high power DC/DC converter. does anyone know of one that fits the bill offhand? or does anyone know of suitably large AC drive that accepts a lower DC bus voltage?

That would take one serious DC-DC converter.

Your problem, besides cost, would be efficiency. Any time you step up voltage you have substantial losses. 20-50% on average. Really, it would be best to just put together 600V worth of batteries.

Batteries are (in general) are priced per Watt-Hour. A 10 kwh battery at 12 volts would probably cost about the same as 10 kwh at 600v.

Here’s a controller made for electric cars by Kelly Controls.

72V,500A,AC Induction Motor Controller

[QUOTE=strantor;9118]…
The problem is, how to get 600VDC from batteries. it would take a ton of them. I have searched the net without much success for a high power DC/DC converter. does anyone know of one that fits the bill offhand? or does anyone know of suitably large AC drive that accepts a lower DC bus voltage?[/QUOTE]
Quick answer - Use DC to AC modified sine wave inverters. Get them rated for the output current that you need. Say 20 Amps in my case. Take them apart and connect to the high voltage DC bus inside, about 150 VDC. Chain them, + to - , together to get the voltage you need. Use one large fork truck battery for each inverter.

Efficiency is not great. Maybe 85%. In my case, 20A of output power gives me 3.5A of heating. 3.5A * 150 VDC means I have to get rid of over 500W of heat per stage.

200VAC 3 phase aussie drives are the lowest V that I have heard of, maybe 200 VDC to 350 VDC range. To get decent horsepower, in the range of 30 - 50, you need to sustain some current from the batteries. In the 120 - 180A range. That’s no problem for lead-acid recycled-from-fork trucks or golf carts sort of batteries. The problem is their weight - 100 - 150 lbs each.

Now for the nitty gritty details, if you’re interested

I am trying the following setup:

Forktruck battery (250+ A-h at 12V), used, heavy
2 - DC to AC modified sine wave inverter with failed AC output sections
Chain together DC/DC section of these inverters to get desired voltage

The DC to DC section steps 12VDC to about 150, maybe 155 VDC for use by the modified AC output stage. The units I have are rated at 2500W continuous, 5000W peak and 1750W continuous, 3500W peak. The DC/DC section is a separate board in the first one, the left side of a board on the second one. Each is connected to the AC stage via a couple of obvious wires.

The output DC is isolated from the input DC by a small, high current step-up transformer. These are similar, and run somewhere above 20 khz.

If things work out (the parts are used/surplus) I’ll chain together 2 units to get 300 - 310 VDC and use that directly to the DC bus of a 208/240 VAC drive which is only 5 HP but will work for testing.

20A at 150 VDC out at 85% efficiency means I need 300A in at 12VDC. I don’t think that used and abused fork truck batteries can sustain anywhere near that discharge rate. I guess I’ll see.

This is a test, since my final objective is to run 930 VDC into the DC bus of a 575 VAC 300 HP drive and use it drive a 40 HP 1770 rpm 324T motor direct-coupled to the drive shaft of my converted chev S10. It works on paper, anyway.

The proposed final setup for the 300 HP VFD is that there will be 6 DC to AC converters (the DC to DC parts only) chained together. That will only give me 20A at 900 - 930 VDC, so a second string of 6 DC to AC converters is used in parallel. 12 of these converters, each powered by a 150 lb forktruck battery takes me over the GVRW for my S10, but I’m hoping that airbags in the back will help the truck to handle better than … a pregnant hippo?

hi guys,

i would like to build a bidirectional DC DC converter for electric vehicle. The converter is a full bridge type with transformer. The question is how is the correct method to select a transformer for this converter? What kind of transformer is suitable for this converter?
Thank you very much!!

[QUOTE=rasyidi;9806]i would like to build a bidirectional DC DC converter for electric vehicle. The converter is a full bridge type with transformer. The question is how is the correct method to select a transformer for this converter? What kind of transformer is suitable for this converter?
Thank you very much!![/QUOTE]

I’m not familiar with a ‘bidirectional DC DC converter’, but that’s likely just a difference in names. I don’t know if I can help, but I’ll need a bit more information.

Hi,
Interesting we share a common interest in making an AC powered EV. I’m an electrical engineer with a small business in AZ supplying sealed lead acid batteries (GEL) and soon Lithium batteries for a wide variety of applications. I’m familiar with VFD/VSD technology but not experienced at programing them or setting them up. I’ve been looking at low voltage units that are supplied with 208 vac 3 phase power. The DC buss voltage will be about 240 VDC. That would be 20 batteries. So very feasible for a battery buss voltage. This technology is widely used in UPS systems. Let me know if you are interested in discussing this further off forum. Terryc at PowerQuality dot ORG
Regards
Terry

[QUOTE=strantor;9118]Hi, I’m new.
Just brainstorming, about making an electric car.
Just to give my background, I’m an industrial electrical controls technician, familiar with installing & setting up 3phase AC inverter drives.

I want to (at some point) make an AC drive car.

I know from the Yaskawa drives that I most familiar with, that you can feed 600VDC to the DC common bus and get 480VAC output. I was pondering if I could find a drive with a bad rectifier section but good inverter section for a discount price, then I could make something work. The problem is, how to get 600VDC from batteries. it would take a ton of them. I have searched the net without much success for a high power DC/DC converter. does anyone know of one that fits the bill offhand? or does anyone know of suitably large AC drive that accepts a lower DC bus voltage?[/QUOTE]

I agreed with Sir Joab. Try to focus your design on drives (inverter + motor) part. Believe me, there is more trouble to face in drives so save your energy in battery or DC-DC part

Hi.

That is what Researchers are working upon ! Power ( Energy Efficiency ) is the key term to keep in mind ! Save this as much as you can .
it is better to concentrate on DC drives ! Another advantage is that if you plan to further modify your design it would be easier to add new Technologies.
and there would be no need of at transformer in working with DC.
Keep DC levels used as close as possible. on other mean use those machine and components which use same level of DC.
Add some Intelligence to your system , it will greatly decrease Power consumption’s and Machine Life ; like adding a micro controller or some thing !
when adding Lights ! check Flux / lumen’s ratios with respect to watts. Check what visibility is required at how much watts !
Break up your design into modules and work on each module separably. list its DC level , connectivity .

work on Aerodynamics manually ( just make your vehicular in near to that shape which causes less friction to air and terrain ).

DC drives can charge your batteries in response when slopping down or clutching ! Regenerative effects.

Thanks.

Your issue, besides price, would be performance. Any time you phase up current you have significant failures. 35-60% on regular. Really, it would be best to just put together 600V value of power supply power. Batteries are (in general) are cost per Watts a Hour. A 10 k-v h power supply at 12 v would probably price about the same as 10 k-v h at 600 -650 v. . . .

I’m waiting for one of you to throw in the Flux Capicator or Dilithium Crystals as being the solution…

Did you guys ever figure out the converter?

I am also working on converting an alternator to a motor which requires a 3 phase input. I was researching on 3 phase to get a better understanding.

I am an electrical and electronics tech but my emphasis is in radio communications. I understand the theories behind it but have not been able to play with 3 phase.

I am trying to take a 24vdc alternator 140amps rated and convert it to a motor. The outputs are unknown since it was rated as an alternator not a motor. I contacted the manufacturer and they said they have no specifications other than: 29 vdc 7amps max on rotor and 36vdc max on each stator winding. The amps are unknown and the tech said to test temperatures while increasing the amperage into the stator. Once the heat reaches to high back the amps down and take notes.