Seeking: ~120V DC 20A supply

Three of us are working on an electric car conversion. We're now working on the "home" charger for it. For that, we are seeking a digitally controllable switcher supply with ~120V output, at up to 20-30A. At these power levels, 240VAC supply is more likely.

Obviously new this will be $$$$, but I wonder if anyone knows of a surplus candidate.

We currently ^H^H^H presently have a 48V 750W supply with remote sense but would prefer something the charge controller can directly manage [We now use a D-A to fake the sense input into giving us our desired output...] as well as being able to charge the whole string at once.

{Question: If you have 3 EE's is that 6E, or (EE)^3?}

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Reply to
David Lesher
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Why do you want an electric car?

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John Larkin                  Highland Technology Inc 
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Reply to
John Larkin

The closest 'standard' item would be a speed control for DC motors; these are intended for inductive loads, a series choke might be appropriate. This one is good for 180V/26A

It's not digitally controlled, though.

I'd think your charger would best be part of the vehicle, you'll want to charge in a remote location someday. Safe connection of 120VDC with a wire and plug is ... difficult (even a fuse is hard to manage for high DC voltage).

Reply to
whit3rd

That's beside the point. Can you help with the requirement?

Reply to
John S

We want to *build* an electric car for the same reason people enter the NYC Marathon, walk on the Serengeti, go to the Moon, and many other challenges.

There are many people who may buy one; that holds no interest to us. As engineers who alas seldom get to actually create, we decided to do just that.

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Reply to
David Lesher

That is a reason to change from our existing thinking. I was hoping someone made a 488 controlled PS, or such.

There will be a lighter, smaller, lower current one on board.

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Reply to
David Lesher

A good candidate might be a multi-kilowatt VF drive and then hack it. Sometimes called VFD, other times just "drive". Even big ones have become quite inexpensive. They come for inputs of 120VAC, 207VAC,

230VAC, 240VAC, 277VAC, and so on. You'd have to remove or disable the bridge at the oupt so you get DC, and then also hack the control circuitry so it doesn't scribe a sine.

Another good candidate could be a huge UPS. One of those server room versions. There are companies that routinely switch them out almost like the batteries, one of the reasons being (like with VF drives) that the electrolytics in there have a finite life span. This would also need to be hacked.

Afraid there is no market for what you are looking for, so not likely surplus gear. What's wrong with faking signals for the sense lines? I do that all the time.

For a loner type nerd that would be a crowd :-)

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Reply to
Joerg

I think if you are going to work with that level of voltage you should incorporate some sort of ground fault sensor to terminate the output immediately if some one comes in contact with it, even if it is floating.

It does not take much to stop the heart.

Jamie

Reply to
Jamie

Presumably, you have a high-current variable supply to run the motor. Can you stick in a relay to flip it around to take rectified line input and charge the battery?

3 EE's are useless. It's like having three watches. One watch and you know what time it is. Three and you're never quite sure. They can't agree on anything.
Reply to
mike

Xantrex and Sorensen (now ametek) made exactly the sort of monster power supplies you need. I think xantrex dropped out of the power supply business, but the tiny bench ones were just rebadged units from the TTI, in the UK.

check test equipment dealers. The really old sorensen stuff will be 1980s goofy linear power supplies with SCR preregulation. Those will be giant, and probably stuffed with obsolete parts. The newer ones are real switching power supplies.

Reply to
Cydrome Leader

What kind of regulation do you need? Current limiting? 120 volts at 30 amps is 3600 watts at the load. The input power will be higher, say 20% higher.

That is definitely 240 volt territory. You are looking at inverter welder technology.

Reply to
tm

Isolation transformer, Variac, bridge rectifier, stepper motor? (hides)

The real classic way is a phase angle dimmer made of a a bridge rectifier followed by an SCR; turn the SCR on sooner in the half-cycle for more current. Use a microcontroller to pick the turn-on point and you have a digital input. (You could argue that this is a switching supply, but it isn't what is normally meant by "switching".)

The power supplies I have used in the past with this kind of juice have been from Sorensen (formerly a tentacle of Raytheon, now owned by somebody named Ametek) and Zivan (an Italian company with US sales). The Sorensen ones are general-purpose supplies and are usually available with both front-panel knobs and remote control. Zivan makes ones that are specifcially designed to be battery chargers for traction applications; the controller is already built in. I don't think the Zivan had any kind of data bus; it did have a few discrete inputs and outputs for things like start/stop, status, and remote sense. It came with a temperature sensor you could put somewhere in your pack to both tailor the charge rate and act as a safety. It also had a blinkenlight to indicate charge states and problems.

One Sorensen supply I used had to send about 48 V at 10 A down several hundred feet of wire to some DC-DC converter bricks that output 5 V and

12 V. Something in this setup broke the regulation in the Sorensen; it would still put out something but it wasn't related to where the knobs were. At least they fixed it reasonably quickly under warranty, and the repaired unit seemed to work OK. I think it had a data bus, but in the prototype stage, the operator just tweaked the front-panel knobs to get "enough" input voltage at the DC-DC bricks.

The Zivan charger I used did just fine at charging a series string of twelve 12 V lead-acid batteries (144 V), but for some reason, had a high leakage to ground on the AC input. It would sometimes pop GFCI outlets or breakers, even when everything was otherwise sound. Non-GFCI outlets/breakers were fine. Other people who had used Zivan chargers reported similar problems. I suspect it may have been designed to a European standard that allows higher leakage current.

I have seen Sorensen power supplies show up at used and surplus electronics dealers. A Zivan probably won't show up used in these places, but a group of electric car home-brewers might be a good place to look. Both are available new, which might help set an upper bound on time or money for a home-made solution.

Some other random things that you probably have already thought of:

Put a simple (maybe electromechanical?) timer somewhere to shut off the charger as a last ditch defense against overcharge... it depends on the pack size, but if you haven't gotten the battery charged in (say) 8 hours, you're probably not going to. This is more important with a home-made charger; commercial chargers often have something like this already.

Give a little thought to interlocking the charger power (AC input must go away before DC output can be disconnected), or select a charge plug that can stand being disconnected under load. Also, interlock the "ignition" of the car and the charger input... the first electric car charger probably got dragged down the street a few days after the first electric car was invented. The "ignition" interlock also helps prevent overloading the charger by trying to run the drive motor while the charger is connected.

A really wide shoe?

Matt Roberds

Reply to
mroberds

Are the electrolytics running too hot, or is there another wear-out mechanism that I don't know about (yet)?

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Reply to
Hal Murray

That does not leave much left now, does it?

Not what we have in mind. We need a switcher supply.

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Reply to
David Lesher

Hardly, the motor controller deals in hundreds of amps, more at peak. Further, we'd have to run its cooling pump. And a relay to switch the output? Huge.

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A host is a host from coast to coast.................wb8foz@nrk.com 
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Reply to
David Lesher

Yes, current limit. But that term basically describes the control input; power supplies limit output, and the consequence reduces both voltage and current furnished to the load.

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A host is a host from coast to coast.................wb8foz@nrk.com 
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Reply to
David Lesher

30

You might want to read this thread, and I have several posts as PStechPaul:

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open-source-59210.html

It is an open source design so you might be able to scale it down for your smaller needs. There have been many suggestions and ideas thrown around. If you are not too concerned about power factor, a simple full wave bridge might be OK, and if you need a higher voltage, a doubler circuit may be the way to go. If you do not mind having high ripple content, you could dispense with a capacitor filter (which causes poor power factor), and use the raw rectified output. Then you can make a simple buck converter that will regulate the portion of the waveform above the battery voltage for charging.

Good luck on your electric car. All we need is a major advance in battery technology or some other small efficient means of converting or storing energy, and they will be very cost effective and "environmentally friendly".

Paul

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Reply to
P E Schoen

On a sunny day (Mon, 5 Nov 2012 02:01:45 -0500) it happened "P E Schoen" wrote in :

Toyota intents to bring a fuel cell powered hydrogen car on the European market in 2013. There is already one fuel station in my country :-)

Reply to
Jan Panteltje

You should ask about this on the electric car forum.

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Mikek

Reply to
amdx

I assume temperature is the #1 culprit. It gets quite toasty in those boxes and they save every penny because the market is so tough since China entered it.

Then there is always the question what quality grade of capacitor they have put in.

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Reply to
Joerg

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