Motor Drive Query

Usually I approach control systems design as custom solution -- to date my customers have all had requirements that pointed to custom boards, or
at least to custom software.
I'm working with a customer who has a square box with plenty of room, so it makes sense to use off the shelf components and rope them together with appropriate cables and glue software, and this is what I'm doing.
My problem is that the motor drive (Teknic) that the customer chose has a very high maximum current value, and we're running into weight constraints in the power supply. Because of the drive's occasional current demands, any switching supply would need to be seriously oversized, expensive, and none too light. The customer currently has a linear supply in there which is better at absorbing the occasional current transient, but it weighs a ton.
I could alleviate many of the power supply constraints if I could get a motor drive that could be configured to drive at a specified current and no higher. Even better would be a drive that can be configured to _consume_ no more than a specified current.
Are there any such critters out there that you know of? The motor is a low-voltage unit; it requires 12-24V or so to operate, so the drive needs to correspond. The drive we're currently using works with a brushless motor with an encoder, and takes a pulse and direction command from the controller -- I'd prefer something similar, but I'd be willing to use a different interface if it meant finding a drive with my desired current control properties.
Thanks in advance.
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Tim Wescott
Wescott Design Services
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Tim, I would go to plcs.net and ask that question. There is a person with the ID of DickDV who works for ABB there. I don't think he is an engineer but seems to have a lot of practical knowledge of how drives of different type work and what drives to use for different applications.
I would try www.eng-tips.com too. There is a special section for motors and drives.
Peter Nachtwey
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Tim Wescott wrote:

How about a little custom circuitry? Sense the current and use it to set a bound. Sensing at low enough resistance is the hardest part of that approach. I have used the drop across the conductor from the controller to the motor.
Jerry
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Jerry Avins wrote:

If I start down that road I'll have an awfully hard time not just building a class-D amplifying stage or three to drive the motor directly. In this case if there's a solution out there that comes in a box, it's more right than any custom thing I whip up.
But if I can't find something, I'll probably do something like that.
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Tim Wescott
Wescott Design Services
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Tim,
No idea what this is doing, but you mention _occasional_ current demands and the motor running off 12-24VDC..
As a really crude solution, how about using an ordinary sealed lead-acid battery sized to the peak current and a battery charger sized to the minimum current??
Cameron:-)
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Cameron Dorrough wrote:

The internal resistance of a lead-acid batterie is exceedingly low. It's not difficult at all to get a burst of 50 amps from a 4 ampere-hour battery. Typical PM motors must be limited to even brief spikes of seven times full-load rated current in order to avoid demagnetizing them.
Jerry
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Tim Wescott wrote:

Update -- I asked before I Googled. It should have been obvious, but there's a whole slew of motor/drive combos that will run straight off of AC, eliminating the need for the power supply altogether.
D'oh.
I'm constantly out of step with this customer -- when I think he hasn't thought things through he shows me up, when I think he's got all his ducks in a row...
It's just a good thing we already know each other...
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Tim Wescott
Wescott Design Services
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