Re: Industrial drives, (was: what is the max bus voltage)

[jcmassey@netspace.net.au]

At 13:19 29/07/02 -0700, you wrote:
>Brian wrote:
>> I am looking at taking a commercially available industrial drive and
>> "reworking" it to make it smaller and lighter. I can choose either a
>> 230 or a 460V unit... 230V drives are significantly larger than 460V
>> drives.
>
>You are running into exactly why most AC EVs use high voltages. It has
>nothing to do with the batteries, motor, or wiring losses -- it is all
>because of the controller.

I have been looking at exactly this, and I can share a few things. Yes, it
is because of the controller. The weight of an Australian 415VAC industrial
drive is half the size and weight of a US 220VAC drive for the same power.
In these controllers Amps = mass. Double the volts, halve the amps, roughly
halve the mass. Why? amps = heat, mostly. Less amps + heat = smaller
everything. If you go this route, use a 3000RPM base speed motor, balanced
to at least 6000RPM, use encoder or equivalent feedback, have an internally
cooled motor, cut half the blades off its internal fan, and add an external
blower. And use a motor of half the voltage rating of the drive, or you
will lack power available at high frequencies.

<snip a bit of Lee's good  comments>

>Back to your problem: If you pick a 460v industrial control, coming up
>with a 650v battery pack will be a challenge! Suppose you converted
>something like a VW Rabbit or Geo Metro; they can carry about 600 lbs of
>batteries. 650v / 12v = 54 batteries, so you're looking for a 12v 11 lbs
>battery. The smallest Hawker Genesis is the 12ah model, which weighs 11
>lbs. List price is around $75 each, so you have $4000 in batteries.

A local conversion has 516V nominal of gel cells. Poor choice of battery,
poor charging control + dying batteries after 5000 kilometers. If he'd been
able to use better batteries it would have been better, maybe...

>Now you need a charger. There will be extreme balancing problems if you
>charge them all in series, so I would break up the pack into 2 to 4
>strings and charge them in parallel or with separate chargers. And, you
>will need some kind of battery monitor or regulator -- 1 per battery.

Exactly. And a 516V or 648V charger will be a special product - although if
you split the pack (and that's split physically, or use isolated chargers)
you could use, for example, two of Rich Rudman's chargers, each set up for
its own group. And you'll need 50 or so battery regulators (so more$$$$).
or your batteries will get out of balance and die.

<snip a bit more good comment>

>> As for working with that high DC voltage, I don't touch anything over
>> 48V so I'd be using insulated tools and MV gloves while working with
>> live battery conections.
>
>As long as you are an electrician familiar with high voltage, and are
>well aware of the precautions and have all the right tools, you should
>be OK. Just remember that it all has to be packaged so no one can get at
>that high voltage!!! Not garage mechanics, not children, not mice --
>nothing!!! And, that it has to be packaged to survive outdoors; in the
>rain, wind, mud, dust, hot, cold, shock and vibration from potholes,
>etc.

Which partly means AGM batteries, and a battery box lid that has
pack-splitting fuses that have to be pulled before you can open the lid.
Our local conversion leaves battery connected to the drives' buss all of
the time, and relies on the control shutdown to lock out. These drives stay
powered in industrial use, but.....

>> I knew there was a small battery efficiency gain by halphing current
>
>No, there is no battery gain. See other postings.

The only real gain is that all industrial drives will provide regen
braking, but this can be done with other means. 

James