From: Max Hall <mhall maxmatic com>
To: noaddress drmm net
Cc: elec-trak cosmos phy tufts edu
Sent: Thu, August 2, 2012 1:39:39 PM
Subject: Re: (ET) Curtis or any generic controller setup - Finally.
Very good prose! Funny stuff, and a nice analogy.
I set up a golfcart controller (vanilla Curtis 36v ser-wound) on an E15 of mine whose controller was vandalized. (Yeah, as I have mentioned a time or two, some a-hole beat up my tractor in the middle of the night. It's a weird world.)
I have not yet added field weakening, though I have meant to get to it. I just run the field and armature in parallel, and have an DPDT switch as an h-bridge for reversing the field current. I have not yet toasted the controller, though I can see how it would happen. And indeed, if you stomp the pedal the thing won't go... and it makes sense that it's because the armature current beats the field current unless you ramp it. I *do* have a fuse on the controller output, and it has never had to give up its life for the controller... yet. It's been a couple years.
Anyway, I picked up a couple of Curtis shunt controllers cheap a while back (for a while they weren;t so pricey on eBay!), so *now* the task I keep not getting to is installing one of them on that selfsame E15.
Anyway, the tractor is buttery smooth with the golf-cart Curtis, even though it tops out pretty slowly w/o the field weakening.
Go ET,
-M
On Thu, Aug 2, 2012 at 12:47 PM, David Roden
<etpost drmm net> wrote:
The video clip is fine as far as it goes, but it left me puzzled. It does
show that the motor reverses, but it doesn't explain what the relays are for
or how they're connected. (Maybe that'll be in next week's episode. ;-)
I'm assuming this is a standard series golf-car motor controller. I've
never tried one with an ET motor, but I know others have. A couple of them
have posted here in past years.
It should work, if you provide some means of ensuring that the field is
powered before you apply voltage to the armature. I suppose you could do
that with a relay, enabling the Curtis's KSI only if field voltage is
present. Even better would be a reed relay that sensed field current
instead - that would prevent enabling the controller if a relay connection
broke or fell off.
One gotcha remains, however. Without a full field in series with the load,
the ET motor may not have enough inductance to make that Curtis happy. Its
current limit may not be able to react fast enough to protect it from
overcurrent. The symptom of this in road EVs is rough, lurching starts when
pulling away from a stop.
This is the best (and by far the most entertaining!) explanation I've read
of how this happens :
http://www.evdl.org/pages/hartcontroller.html
If the controller is sufficiently oversized, it might survive just fine, at
least under normal operating conditions, but there's still some risk.
David Roden - Akron, Ohio, USA
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