The 'Toaster' - How does it function?

The 'Toaster' - How does it function?

Postby colinmcc » Tue Jan 22, 2013 6:45 pm

Can anyone please point me at (or write?) a good description of the 'toaster', its use and function in controlling the speed of a large frame Elec-Trak?

Thanks,

Colin
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Re: The 'Toaster' - How does it function?

Postby admin » Tue Jan 22, 2013 7:06 pm

Good question, that i have found people do not ask. Here is how it was explained to me.

The "toaster" is a large resistor. It's purpose is to lower the the armature voltage thus slowing down the motor. Resistance causes heat, hence "toaster".

The proper way to drive an ET is to select a mechanical gear, which when in electronic speed 3 (full 36v), matches your required ground speed.

Speeds 1 + 2 which send power through the toaster should only be used to get you smoothly to your desired ground speed, which you set mechanically through the transmission. If you find yourself hanging out in one of the resistive speeds then you need to change to a different mechanical gear.

Without the toaster the motor would jump to a full 36v.
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Re: The 'Toaster' - How does it function?

Postby Bushman » Tue Jan 22, 2013 7:08 pm

The toaster is just a resistive element that provides some voltage drop from the battery bank to the drive motor armature. On everything up to the E20/C-185/I-5 there are 3 armature speeds: 1. entire resistor band (~28V), 2. half the resistor band (~32V), and 3. none (full 36V). On the E20, there are 4 armature speeds, splitting up a larger/longer resistive element into 3 sections instead of 2.

These speeds are selected via the speed control by effectively energizing small coils(contactors) to short each section of the resistor band, providing an alternate path of lesser resistance to the armature. So, in the final armature speed and beyond, no current should be flowing through the toaster. It should be flowing directly through the speed selector coils to the armature.

Is that a good explanation?
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Re: The 'Toaster' - How does it function?

Postby colinmcc » Wed Jan 23, 2013 1:55 am

Thanks, both of you!

These speeds are selected via the speed control by effectively energizing small coils(contactors) to short each section of the resistor band, providing an alternate path of lesser resistance to the armature. So, in the final armature speed and beyond, no current should be flowing through the toaster. It should be flowing directly through the speed selector coils(?) to the armature.


Ah, so in models less than E20/I-5 there must be 2 sets of contacts each shorting out one of 2 sections of the resistor? And, the 'shorted' path is through the closed contacts which are closed by energising the coil(s), but no armature current actually flows through the coils..

I'm heading to Geo's pages to see if I can find a circuit diagram.

Edit: Found pics at http://watts-up-elec-traks.com/Page_8.html So yes, neither shorted, one shorted, both shorted = 3 different current paths/voltage drops.
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Re: The 'Toaster' - How does it function?

Postby Bushman » Wed Jan 23, 2013 3:08 pm

Yes Colin, that is correct. There are three Normally Open contactors for the E-20 and two NO contactors on everything else. They are usually referred to as 1A, 2A, and for the E-20, 3A is added. When the contacts are closed, the armature current runs through those contactors INSTEAD of running through the resistor band. The coils for those contactors are energized via the speed control microswitches, no matter whether it's a foot-pedal or a hand throttle.
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Re: The 'Toaster' - How does it function?

Postby RJ Kanary » Mon Jan 28, 2013 2:11 am

A small correction concerning the armature control scheme on the E-20.The EARLY models had eight motor speeds, the later ones had only seven.The AA through DA models, {With some blurring of borders between sub sets.} had three armature resistor bypass contactors.The later production had only two.The additional armature resistor used in the eight speed models made for a much smoother launch. [ Easily identified by the penthouse atop the charger/resistor cover.] Likely this was deleted in the interest of cost cutting in subsequent production. :(
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