[McRat]

I'm at the Forrest Gump stage here. So bear with me.

For brush-type motors:

Since the electric motor has resistance, can I just run a powerful solenoid and a push button for the throttle? I would put temp sensors on the batteries and motor, which would kill the relay that fires the solenoid. And a voltage cutoff diode to avoid excessive discharge. Basically, no controller at all.

This is a race application, and hybrid, so the electric motor is more like a nitrous shot than a gas pedal.

[somanywelps]

This is known as a contractor bypass.

The motor can handle X current, and the batteries have a current limit too.

When RPM is zero, resistance is theoretically zero, so current is infinite.

Which means either your batteries or motor will explode or ignite in a matter of seconds unless it's a VERY low power system or you only do it for a fraction of a second.

(You need a controller)

[major]

Originally Posted by McRat

I'm at the Forrest Gump stage here. So bear with me.

For brush-type motors:

Since the electric motor has resistance, can I just run a powerful solenoid and a push button for the throttle? I would put temp sensors on the batteries and motor, which would kill the relay that fires the solenoid. And a voltage cutoff diode to avoid excessive discharge. Basically, no controller at all.

This is a race application, and hybrid, so the electric motor is more like a nitrous shot than a gas pedal.

Hi Rat,

I did this. With the students on the go kart race team. They were in transition from E85 5.5hp Honda engines to battery powered electric for the university competition. So we took a ICE powered kart and put a second sprocket on the axle with a chain to a 4 inch series motor. Two 12V 18Ah PbAcid batteries and a big old Albright contactor. Push button on the steering wheel and diode on the motor. Provided a real good boost. Only used a few times and then the kart went into full electric mode.

Things can work well at 12 and 24 volts up to 100's of amps. Like the cranking motor on your ICE. But the voltage and current levels you seek make such "simple" solutions out-of-the-question. You'd be lucky to get it to work once.

Regards,

major

[McRat]

So if I do it, I should have a camera setup so it can get on "World's Dumbest Drivers 22"?

OK, thanks! I won't do that.

[Ziggythewiz]

My new favorite show is called Insane or Inspired. I think this would make for a great segment.

I had planned something similar as a controller bypass to go past my 120V limit, complete with mad scientist knife switch and all...but I happened to compare my gear ratios with my motor's max RPM and found that my goal (0-60 mph in 2nd) would have blown up the engine.

[ruckus]

Ok, bear with me for a second..

Does anybody remember a guy a few years back with a voltage selector that looked like a wwII ship speed selector (all ahead 3/4)?

His setup was called something like 'cheap ev drive' or something.

He drag raced his boat of a car and actually did pretty good using an old 13" series dc or something.

Anyway, if anybody remembers, he had some sort of trick (made with wood from the garage) 'power selector'.

Anyone remember? I'll try to dig up some old pics...

Edit: now I remember it was 'poormansev.com' or something similar. Here is his 'controller'



You gotta respect that kind of ingenuity...

I can hear Tesseract saying "damn, if only I had thought of that..."

[PStechPaul]

There are high power tap switches (or transformer tap changers), but they're big and expensive. It's probably better to use contactors (and really a controller is the right way to go). Here are some:
http://www.surplussales.com/switches/SWPowerTap.html

Like this:

[McRat]

Originally Posted by ruckus

Ok, bear with me for a second..

Does anybody remember a guy a few years back with a voltage selector that looked like a wwII ship speed selector (all ahead 3/4)?

His setup was called something like 'cheap ev drive' or something.

He drag raced his boat of a car and actually did pretty good using an old 13" series dc or something.

Anyway, if anybody remembers, he had some sort of trick (made with wood from the garage) 'power selector'.

Anyone remember? I'll try to dig up some old pics...

Edit: now I remember it was 'poormansev.com' or something similar. Here is his 'controller'



You gotta respect that kind of ingenuity...

I can hear Tesseract saying "damn, if only I had thought of that..."

Problem with that? Wouldn't it drain the batteries unequally, so you'd have have progressively less capacity as the voltage went up?
In other words, you'd be limited by the capacity available from stage 1?

How about a Poor Man's PWM -
A small motor spins a drum with many narrow contacts all going to the batteries.
You have multiple brushes you can engage with a lever, staged so they increase the % of ON time.

Say the drum has 12 contacts. When one brush contacts, it would be 1/12 power, when 2 brushes are down, it would be 1/6, 3 brushes down, 1/4, ... 12 brushes down is full 100% duty.

Hmmm... Too complicated. Like a venier scale on a pair of calipers, the number of brushes is less that the number of contacts. As you rotate the brush collar it goes from no contact, to brief contact, to constant contact in a small rotation of the collar? No, that's not right, but it's close. You can do mechanical PWM.

Put some capacitors on it to smooth it out, and you'd have a ghetto PWM speed control. Mechanical. Current limit would depend on the contacts and brushes.

[McRat]

No, the drum with contacts has different lengths of contacts.

You use one big brush that is wide enough to cover two contacts.

The brush collar slides down the rotating contact drum.

At first, nothing.
Then it hits 1 contact per rev
Then 2 contacts per rev,
Then 3 ...
When it get to the far end of the drum, since the brush is wide enough to hit two contacts, it is always connected, and at 100% duty.

[Ziggythewiz]

Originally Posted by McRat

Problem with that? Wouldn't it drain the batteries unequally, so you'd have have progressively less capacity as the voltage went up?

Yeah, shouldn't be difficult. Just calculate how long you'd expect to use each level. and size em accordingly. 1st batt 200 AH, 2nd 175 etc. You just have to get in the ballpack and the floodies will balance themselves to make up the difference (let's face it, if that's your controller you're not running lithium).