RE: (ET) Oscilation on the FW dropout circuit

["Markus Lorch" <mlorch vt edu>]

Hi Chris,

this is consistent with the behavior of my E20. The FW relay
will drop/kick-in at a frequency of about 2 herz at most. I usually
reduce the throttle to speed for once it clicks 2 or more times if
I know that the load condition is not just temporary but e.g. a longer
incline. 

My E20 needs quite a bit more power to move around swiftly now that
I have 6 golf cart batteries in it. Before I had the 100Ah AGM batteries
which are probably only 1/2 the weight. The difference is very noticible
on inclines and when starting from a dead stop. I guess that also the
AGMs could deliver a higher current than the golf cart batteries so that 
the effect is even larger. 

On the other hand, the golf cart batteries seem to last forever - they
are real workhorses :)

ok, now gotta go and catch our plane to Germany, we'll leave in a few hours

Markus



> -----Original Message-----
> From: elec-trak-bounces cosmos phy tufts edu 
> [mailto:elec-trak-bounces cosmos phy tufts edu] On Behalf Of 
> Christopher Zach
> Sent: Tuesday, May 10, 2005 10:46 PM
> To: Elec-trak list
> Subject: (ET) Oscilation on the FW dropout circuit
> 
> 
> Ok, so I finally replaced the flakey card4 with a nice new one. Now I 
> have a bit of a problem.
> 
> When I power up a hill in speed 8, the tractor of course 
> slows down and 
> current goes thru the roof. This causes the current on the 
> shunt to go 
> way up, which causes the card 4 circuit to drop power to the 
> FW bypass 
> relay.
> 
> Thus the relay drops, the FW resistors are shorted and power drops to 
> the motor. However this causes the current on the shunt to 
> fall, which 
> causes the relay to click back on, which re-engages the FW resistors, 
> which causes the current to skyrocket again, etc.
> 
> Net result is a buzzing on the relay as it drops in and out 
> which can't 
> be good.
> 
> Is this normal? I'm thinking of building a lock-out circuit that will 
> tie into the other poles on the relay and cause it to stay out if it 
> overloads for 5-10 seconds or something. Any thoughts?
> 
> Chris
> 
> 
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