I'm quite busy at the moment (school work) but I will finish the relay driver shortly.

So here's the plan:

When accelerating forward, motor is put into forward position using relays. MOSFET is driven with a PWM signal through a gate driver IC.

When accelerating backwards, motor is put into backwards position using relays. MOSFET is driven with a PWM signal through a gate driver IC. Max speed in reverse 50-60% full speed.

Correct.

When pot released, MOSFET switching stops, and relays connect to the resistive brake. (Maybe make it so they don't connect to the resistive brake? But it would require 4 relays total, or another power MOSFET.)

When E-brake pressed, both relays connect to resistive brake. After 3 seconds (RC delay - approximate) the relay connects to the shorted position so the motor stalls. MOSFET switching is also inhibited.

.
The whole idea about breaking is a bit perplexing as I do not know if the new motor controller will react differently from the old one with respect to the slowing of the scooter.

A few more specs of the operation of the old motor controller.
Speed: - 4.25mph
reverse - 60%
Range/charge - 25mi. Ha!
Braking - Electronic regenerative, electromechanical.

I removed the electromechanical braking as I was not too keen on it's jerking stop. The combination of friction, electronic regenerative braking brought the scooter to stop reasonable quick (within 2ft - 3ft max, maybe 5ft on hills.)
Thus I'd be more inclined to pursue the regenerative breaking and leave out the resistive breaking, in other words, follow RB's method of a half-bridge.
What are your thoughts?

So the final solution requires 3-4 relays and one or two MOSFETs to add all the requested features. Is this good for you?

Not sure just yet.

I should be able to use two LM324s and some 2N2222 transistors for the most part, and a gate driver IC from Microchip.[/QUOTE]

Do you have a program to simulate this circuit. I have pretty much all the parts. MOSFETS, transistors, Relay's, etc. except the gate driver IC from Microchip you would want to order. I too have a parts order pending and could add the gate driver IC to it. Would just need the part number.

I think it will be best to keep all relays off the main PCB - and just solder wires to the terminals and connect those to the PCB. This would also make the PCB smaller and cheaper.

The relay's, if 4 are required can certainly be off the printed circuit board and
wired via connectors.

 

I see it as being a much better option than a braking resistor. Not only does it remove the need for the braking resistor, and the heat generated, but will also improve economy.

 

Regenerative braking can be added then. The only thing to be worried about though is what to do when the battery is full. We want to still be able to brake even when the battery is floating at ~27.5V. I'm worried that the battery will give that sudden braking feature that you didn't like with the last brake/motor controller.

 

Regenerative braking can be added then. The only thing to be worried about though is what to do when the battery is full. We want to still be able to brake even when the battery is floating at ~27.5V. I'm worried that the battery will give that sudden braking feature that you didn't like with the last brake/motor controller.

When the electromechanical braking mechanism was installed, lifting my hand from the throttle would give me the sudden jolt stop and keep the scooter fixed even on a hill. When I removed the electromechanical braking, leaving just the regenerative braking, the scooter slowed down fairly quickly, but was not fixed on a hill. It would drift down very slowly. Also after removal of the electromechanical braking, the scooter would coast if the power was turned off.
So I am inclined to just go with the regenerative braking and deal with the fixing of the scooter on a hill to possibly a purely mechanical method. In other words, if throttle is off, I can brake with hand device. There is actually a need to be able to push the scooter freely. There was a lever that released the electromechanical brake just for that purpose. How about a 100W 10 Ohm slide-pot!!! Ha! don't think they exist. This, of course, is not purely mechanical.

 

When the electromechanical braking mechanism was installed, lifting my hand from the throttle would give me the sudden jolt stop and keep the scooter fixed even on a hill. When I removed the electromechanical braking, leaving just the regenerative braking, the scooter slowed down fairly quickly, but was not fixed on a hill. It would drift down very slowly. Also after removal of the electromechanical braking, the scooter would coast if the power was turned off.
So I am inclined to just go with the regenerative braking and deal with the fixing of the scooter on a hill to possibly a purely mechanical method. In other words, if throttle is off, I can brake with hand device. There is actually a need to be able to push the scooter freely. There was a lever that released the electromechanical brake just for that purpose. How about a 100W 10 Ohm slide-pot!!! Ha! don't think they exist. This, of course, is not purely mechanical.

Such 100W devices do exist, look up salt water rheostats .

Does anyone know how to limit the current into the battery? I'm worried that the back EMF could be much higher than the nominal voltage, which could damage the battery. We only want to charge it when the battery is below 27.5V, otherwise we could overcharge it.

 

A good question to pose. I doubt, however, that the regenerative braking will provide so much current that we would over charge the batt's, especially while in use, but I'm not the expert by far.

 

A good question to pose. I doubt, however, that the regenerative braking will provide so much current that we would over charge the batt's, especially while in use, but I'm not the expert by far.

It's possible that if you were, say, on a hill, that the regen would be putting more energy into the battery than came out...

So I think there should at least be a backup braking array.

 

It's possible that if you were, say, on a hill, that the regen would be putting more energy into the battery than came out...

So I think there should at least be a backup braking array.

O.K. So when I'm on a hill and I want to stop the scooter completely and make it unmovable we can indeed use a resistive array of sorts. I'd almost like to design it as a separate entity. Turn the scooter off and if this alone does not keep the scooter fixed, then engage the resistive brake, ie, the 100W 10 Ohm slide pot, or something as such. I'd rather we did not put off the controller circuit too much designing and adding this in.

Variable Resistor
When power switch is in the on position the relay disconnects the resistor, when the power switch is in the off position it connects the resistor and a manual adjustment can be made.

 

O.K. So when I'm on a hill and I want to stop the scooter completely and make it unmovable we can indeed use a resistive array of sorts. I'd almost like to design it as a separate entity. Turn the scooter off and if this alone does not keep the scooter fixed, then engage the resistive brake, ie, the 100W 10 Ohm slide pot, or something as such. I'd rather we did not put off the controller circuit too much designing and adding this in.

Variable Resistor
When power switch is in the on position the relay disconnects the resistor, when the power switch is in the off position it connects the resistor and a manual adjustment can be made.

Okay. I'll see what I can do.

 

Relay drive done.

This drives four relays. It uses one LM324 and 10 x 2N2222 transistors. I extensively use transistors where possible, to reduce the cost and size of the board.

Next step; motor control, PWM, and power supply. Those parts will be easier.

 

Relay drive done.

This drives four relays. It uses one LM324 and 10 x 2N2222 transistors. I extensively use transistors where possible, to reduce the cost and size of the board.

Next step; motor control, PWM, and power supply. Those parts will be easier.

It's looking pretty nice. Good work.

 

It's looking pretty nice. Good work.

Thanks.

We need to decide on the rectifier used to convert the motor's AC to DC for charging the battery. Rated for maybe 8-10 amps.

 

Thanks.

We need to decide on the rectifier used to convert the motor's AC to DC for charging the battery. Rated for maybe 8-10 amps.

Don't understand the reason to rectify the out put when in regen mode?

The out put will/should be DC to begin with. Think of a old time car that had a generator, the out put was DC. A brushed DC motor is just a generator with reversed input.

 

I think I'm in agreement with shortbus on this one. It's a DC motor. If DC makes it spin then spinning it makes DC, Yes?

Thanks for the input, shortbus!

 

I think I'm in agreement with shortbus on this one. It's a DC motor. If DC makes it spin then spinning it makes DC, Yes?

Thanks for the input, shortbus!

Okay, in which case I'll omit the bridge but we will still need a diode to prevent the motor spinning when batt voltage < motor EMF. To lower costs, I'll use the same Schottky we use for other parts.

It looks like 5 relays are necessary, damn this thing gets more and more complex the more I think about it! The 5th relay controls motor GND terminal, if it wasn't there then the motor + would be shorted to GND a lot of the time.

 

Here is the motor driver circuit, the board will use 3 pin connectors for connecting to the off-board relays.

 

The parts count is mounting up. Maybe you can give me the Mouser part numbers and I can order them to be sent to my house for assembly. If not I'll be paying shipment charges to your place and then from your place to mine. Of course this is after all circuits are final.

 

The parts count is mounting up. Maybe you can give me the Mouser part numbers and I can order them to be sent to my house for assembly. If not I'll be paying shipment charges to your place and then from your place to mine. Of course this is after all circuits are final.

Well I was thinking of using the relay you pointed to a while back on digikey; order 5 of them plus 1 spare. And MOSFET and diode as you spec'd.

I have good standing with many distributors - they'll probably let me ship it directly to you.

 

Well I was thinking of using the relay you pointed to a while back on digikey; order 5 of them plus 1 spare. And MOSFET and diode as you spec'd.

I have good standing with many distributors - they'll probably let me ship it directly to you.

I already have 3 of the Relays and would need 3 more. The only problem is that shipping on 3 parts will be ridiculous since I have a large order from mouser pending. Don't know if you had orders pending from Digikey or not. I might be able to get 6 Relays from Mouser cheaper than 3 from Digikey.

 

I already have 3 of the Relays and would need 3 more. The only problem is that shipping on 3 parts will be ridiculous since I have a large order from mouser pending. Don't know if you had orders pending from Digikey or not. I might be able to get 6 Relays from Mouser cheaper than 3 from Digikey.

Remember, you'll also be ordering a power MOSFET, and three diodes, plus spares. And the gate driver IC if you don't have one already. So shipping starts to be more reasonable.