[onegreenev]

Poormans EV was setup so the batteries were all used for each voltage setting. The setup was complex but it did work. Takes up lots of space and it has lots of copper connectors and contractors to switch the pack around for each voltage. It works and is pretty basic. Multi speed and multi geared so if you know how to do it right you can really have a good running car. No amperage control. It just uses what the batteries can deliver.

Pete

The rotary switch is a good idea but switching while under load will cause the switch to burn and pit during the switch. I have a small rotary switch for my Cushman Truckster. It works and even has reverse but one leg is nearly useless but it did last many years of use. Still works. Full resistor contactor setup and three speeds. Works great. 6, 12 and 24 volt setting.

[Woodsmith]

Originally Posted by McRat

How about a Poor Man's PWM -
A small motor spins a drum with many narrow contacts all going to the batteries.

Been done.

SimonRafferty on this forum did it as a controller for his Robot Wars competitor.

I also had a go at a small scale mock up to examine the practicalities and videoed it.


I like the steam punkness of the concept and would love to have the set up in a glass bubble arcing away for all to see.
It isn't really practical for vehicle power levels though, and a lot of work for a low power system.

[Qer]

Originally Posted by 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.

*ROFL*

Originally Posted by ruckus

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..."

Mmmm. Naw. I think we can still motivate why kA has to be handled by a more intelligent controller.

The problems are two as I see it. The first is that it's very up to the driver to switch voltages at the right time (making it one more thing to keep track of + that shifting at the wrong time will make you either lose the sweet spot or blow up the whole contraption) and the second is that the contactors you'll need won't be cheap (unless you find them on the junk yard of course).

The contactors in the Solitons are for example always switched at no load since switching them at full load would wear them out. They CAN shut down full current in an emergency for safety reasons but it's definitely not good for them in the long run. There IS of course contactors that can handle this kind of currents but, well, the price tag isn't DIY-friendly...

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?
In other words, you'd be limited by the capacity available from stage 1?

Yep. That too. Your start current would be a lot lower than it would be with a PWM-controller too since a controller "trades" Voltages for Amps. A dumb switch can't "trade" the same way so the max current from the batteries will be a harder limit.

Originally Posted by McRat

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.

There has been some experimenting with that, but I've never seen anyone complete one in full scale suitable for an EV. My guess (since noone has even reported trying more than small proof of concept models) is that trying to control hundreds of Amps (or some kA) will quickly wear the contact fields out due to arching and that in the end it'll get more expensive and probably a lot less reliable than silicon.

[Dennis]

If things do not blow up, then a dragster built with direct connect via a contractor would win against a dragster with a motor controller with current limit. I am not sure anyone has successfully got such at setup working without the consequences of huge plasma fireballs shooting out of the motor's commutator section or battery terminals literally exploding off the batteries.

I had someone ignore my advice of using a motor controller. He had a 48 volt set up and used an Albright sw-200 contactor. When the contactor engaged it literally melted into molten copper in the contact area of the contactor and the motor shot out huge plasma fireballs from the motor's vent shroud that surrounds the commutator side of the motor. The brushes vaporized off the surface of the commutator and some of the commutator bars where fused together. Lucky for him the motor stood still this whole time.

[PStechPaul]

I can see where direct torque control (or current control) is ideal for dragsters because it will instantly compensate for wheel slip and adjust the PWM for maximum acceleration. Without that, using a direct battery connection to the motor (and asssuming a series wound traction motor), it would tend to spin the tires and reach maximum RPM as determined by the voltage and the friction of the tires on the track surface.

With the direct battery connection the only limitation will be the resistance of the conductors and the motor winding and the battery. It might survive a lead-acid battery but probably not Lithium with much higher peak capacity.

[Qer]

Originally Posted by Dennis

If things do not blow up, then a dragster built with direct connect via a contractor would win against a dragster with a motor controller with current limit.

Provided the tires can keep the grip on the pavement and that the transmission survives the brutal torque the almost short circuit current will result in and that the pack can survive being near short circuited and the contactor actually manages to make before being burned up in a huge cloud of plasma and that the brushes won't go kablam within seconds and that the driver will be able to keep the car straight when it takes off at an insane acceleration and whatever I've forgotten to mention and .....

No. I don't think a dragster using connectors will be able to win against one with a controller, because I think the best case scenario is that it breaks down at the start and the worst case scenario will be that it'll be bolting off completely uncontrollable in a random direction and cause mayhem and chaos.

The only way a contraption like that would be controllable is if it has batteries that sag enough to make the current controllable (did anyone say lead-acid...?) but then it won't win anything...

[PStechPaul]

Also, the tap select contraption seems to have a relatively light gauge wire (maybe #10 AWG) on the arm, and the bolts may be steel, so that will add resistance. Actually if that is a blue barrel crimp connector it may be only #14-#16. A 6 foot loop of #14 wire at 0.0025 ohms/foot has 0.015 ohms which limits the current from a 12 volt battery to 800 amps, which is in the safe range for the battery and motor, but not for the wire. Assuming a locked rotor condition, this is 9600 watts, which would quickly melt the insulation and vaporize the wire within less than 50 mSec (WAG), but if the motor spins within that timeframe it will generate BEMF and reduce the current. Obviously this is a very unsafe and inefficient setup, but its very crudeness may save it from catastrophe. But an otherwise well-designed setup, using heavy cables and a high current contactor, will be able to deliver the sort of current and power to the motor which resulted in its spectacular destruction.

I want video!

[Ziggythewiz]

It was already posted that the contraption you're referring to was driving contactors, not a traction circuit, so safety and inefficiencies at the selector arm are irrelevant.

[PStechPaul]

OK, that makes a little more sense. Here is the website which shows the schematic and the technique required for using it in drag racing:
http://www.poormansev.com/id24.html

It has a 6V battery which sort of provides an "idle" and then the other batteries were selected 48 volts per click, and not in a series/parallel configuration as suggested.

His latest controller using 2000 amps of resistance wire seems like an incredible waste of power, but I guess it works. And the salt water immersion tank is pretty crazy unless you can use the Hydrogen and oxygen it produces without blowing up.

His motives are stated to be that he can't afford a proper size solid state controller, but I think it is more that he understands mechanical and basic electrical principles and perhaps has the parts and materials and tools to put them together for little cost.

But, hey, whatever floats (or tows) your boat!

[Jamie EV]

Actually, the guy with the ship's throttle lever is not wasting much energy at all. He's doing something old school and clever. First setting is all batteries in parallel....12 volts.....second setting is 4 strings of batts....24....next setting is three strings.....36....2 strings......48....all series....96 volts and he's flying!

Works perfectly find actually and if he wants to he can add a "slot car" style resister spring to control the intermediate voltage between these settings. So it's like a gear shifter and a pedal....the energy wasted is in teh heat of a resistor spring...but you know

I've been thinking about making a huge heat sunk resistor spring like that. Could make it out of cheap parts. Yes it's a waste of energy but if you can't afford anything cheaper...it's a solution...also I could use the heat in the cabin in the winter lol.

Man the heat would be incredible.