Re: (ET) Testing lift motor at higher voltages

["Christopher Zach" <cz alembic crystel com>]

That's because the internal breaker is rated for 12 volts. No problem 
there,
it can probably open a 12 volt shorted load all day.

18 volts less so, 30 volts and it isn't going to happen :-) But you need 
30a
at 12-18 volts to lift things. 

I'll see how it does with a 20, might de-rate the fuse to 15a. There
wouldn't happen to be a breaker that fits in an ABC fuse slot and is rated
to break a 36 volt load, is there?

C

-----Original Message-----
From: RJ Kanary [mailto:rjkanary consolidated net] 
Sent: Sunday, December 23, 2012 7:24 PM
To: Christopher Zach; et
Subject: Re: (ET) Testing lift motor at higher voltages

Bear in mind that the Delco motor has a high failure rate with the internal
circuit breaker. On occasion, one will fail open.Unfortunately,the vast
majority of them weld shut.In the time it takes for the 30A Slo BloR fuse 
to
open however, permanent damage has occurred.The primary job of THAT fuse is
to protect the wiring, not the load.
I have replaced the fuse with a 15 or 20A self-resetting circuit breaker to
stave off that type of disaster.

RJ


On 12/23/2012 6:41 PM, Christopher Zach wrote:
>
> Well, keep in mind that the lift motor does not have permanent 
> magnets. It's actually a series wound motor with two field windings.
> The power path goes from the battery, to the switch, to one or the 
> other field, to the armature, and then back to the battery.
>
> The result is the motor **is** a series motor, so as the load 
> increases the draw on the field and armature increases as well.
> Likewise if you double the voltage you double the field strength and 
> the armature strength so power output doubles.
>
> I think the key danger is heat; more power means more heat in the 
> motor and too much heat will short out the windings as the insulation 
> melts. However if it can get the blower lifted in 3 seconds instead of 
> 10-15 (what it takes when it's struggling at 18
> volts) then that could mean the motor suffers **less** damage at 30 
> volts than 18. Maybe.
>
> Chris
>
> *From:*Rob Brockway [mailto:getractor yahoo com]
> *Sent:* Sunday, December 23, 2012 6:31 PM
> *To:* Christopher Zach; Elec-Trak
> *Subject:* Re: (ET) Testing lift motor at higher voltages
>
> I don't know how accurate this is, but I have heard that a lot of DC 
> motors are designed so they have a 50% voltage safety factor so you 
> don't demagnetize the permanent magnets. So a 12 volt motor design 
> will likely demag at 18 volts or higher (at locked armature amps).
> Interestingly if you demagnetize the motor speed will tend to increase 
> under light load.
>
> Rob
>
> *From:*Christopher Zach <cz alembic crystel com 
> <mailto:cz alembic crystel com>>
> *To:* Elec-Trak <elec-trak cosmos phy tufts edu 
> <mailto:elec-trak cosmos phy tufts edu>>
> *Sent:* Sunday, December 23, 2012 4:16 PM
> *Subject:* (ET) Testing lift motor at higher voltages
>
> So this afternoon I had to switch the E20 over from mowing to 
> snowblower. Note that it is **much** easier to do when you put the 
> snowblower on two moving dollies. They're a good height, and it's a 
> snap to roll the thing around the shed.
>
> At the same time I figured I would try to boost the voltage draw for 
> my lift motor. Normally it's tapped to 18 or so volts on the BB600 
> pack, right about the middle. The next closest battery terminal would 
> be 30 volts, so I gave that a shot.
>
> **wow**. Motor zips up and down fast, lifts deck as if it was not 
> there. So I removed the deck and put on the snowblower. Greased the 
> lift pulley and gave it a shot.
>
> **wow**. Motor zips up and down fast, lifts snowblower as if it was 
> not there. This is good, as normally the motor struggles to lift the 
> blower and sometimes stalls. Now it runs it right up in a few seconds. 
> In fact I worry that I will rip something out if it hits the highest 
> lift point. So I reduced the lift fuse from 30a to 20a.
>
> Now, this is a "new" lift motor from Bill Gunn, top of the line. Not 
> sure how long it's going to last with this, but I did note that it's 
> duty cycle is now a lot less since it's not farting around struggling 
> to lift. Zip it's up in 3-4 seconds. Then off.
>
> So now I am thinking: One of the big problems with the lift is that 
> the motor will stall out sometimes and then trip it's breaker.
> Stalling a DC motor puts a lot of strain on the commutator bars and 
> the brushes. Is it better to have the motor still spinning (and pretty 
> quickly I might add) at 2.5 times it's rating? Seems like it would be 
> drawing less current, which is good. So what's the downside?
>
> I wonder what the switch in the lift is rated at. If I'm opening and 
> closing way above its rating, that might blow up.
>
> Chris
>
>
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