electric motor cycle

[TFC]

I am building an electric motor cycle. the motor is 24V DC at around 2kw. the PWM controller I have is 24V DC but the max allowable current is only 20amps.
I do have a high current switch (possibly a Tric) that came with the motor But I don't know how to make the two units work together. the output of the controller is negative, and the gate input on the high current switch is positive.. the Gate needs a miniumin of 6volts at 15mA to triger.
Is there anyone who can help me design an Interface circuit?
Theo

 

[Pommie]

Do you have links to the parts?

Mike.

 

[TFC]

NO Sorry. I purchased the electric bike scooter accessories motor brushed controller and throttle twist grip 24V 250W from Outdoor Riding accessories store at Aliexpress. the high current switch came with the motor but has no part numbers on it. I have tested it and it switches ok at 6volts and 15mA positive on gate

 

[TFC]

 

[TFC]

The motor runs well with no load nice and smooth and great control. But I dear not put a load (other than the back wheel which is off the ground) as the current will increase over the 20amps.

 

[alec_t]

Welcome to ETO!
Are you UK/Europe-based? If so, check out this.

 

[TFC]

No I am in NZ.
The motor cycle i am building is a small but full motor bike so will be registered for the road just the same as other motor bikes.
But thanks for the interesting article.

 

[TFC]

I have had a "little" success using a BTA 08-600 triac to put a positive feed to the high current switch. using resisters to lower the current to the gates.
but the control is very poor. my DC volt meter show's it's switching the motor on at 7volts but stopping at 17volts (should be 0 - 23volts)
any thoughts?

 

[rjenkinsgb]

the motor is 24V DC at around 2kw.

I've got to be blunt, that is not a good choice.

2KW running on 24V would be around 84A before inefficiencies; possibly nearer 100A from the batteries to get 2KW output.
Batteries that can sustain that current without damage would be extremely large; most types would just overheat and be wrecked.

That's why most higher power electric bikes / scooters use rather high voltages, as a higher voltage means proportionally less current for the same power.

 

[TFC]

"Understood." that makes sense. however this is just a fun project and not intended for normal use. also the budget is low.

 

[ChrisP58]

I have had a "little" success using a BTA 08-600 triac to put a positive feed to the high current switch. using resisters to lower the current to the gates.
but the control is very poor. my DC volt meter show's it's switching the motor on at 7volts but stopping at 17volts (should be 0 - 23volts)
any thoughts?

Sorry. You can't use a triac for DC. At least not if you want to be able to turn it off.

Triacs are latching devices and keep conducting as long as the current through them is above their holding current. When used with AC, that happens with each zero crossing, but with DC, it doesn't happen unless something else breaks the current.

 

[TFC]

thanks ChrisP58. as stated earlier the gate feed will be PWM so turn off all the time.
I am a bit disappointed so far with this post feed as all I have heard is negatives. not one helpful input has emerged.

I have got it going using the BTA 08-600 triac but Its the niceties of the circuit, like current limiting of the gate that I was hoping to learn about.
If anyone has any helpful info. for me that would be great.

And thanks to the people who have posted I do appreciate your thoughts but they aren't helpful.

 

[rjenkinsgb]

OK, just be aware a different setup may be cheaper than making something to suit what you have!

A conventional thyristor or triac will only turn off again if the load current (not gate current) is interrupted externally; eg. they are great on AC supplies, where the supply reverses through zero, but useless on DC.

(A BTA08 is also only rated 8A, you need something rated well above 100A to suit the motor).


You would need a large power FET (or several in parallel) or possibly a large IGBT. The current rating should ideally be well above the maximum possible motor current.
If you want to reverse it electronically, you need four in "full bridge" configuration.

These look to be a reasonable rating?

N-Channel MOSFET, 150 A, 150 V, 4-Pin SOT-227 IXYS IXFN180N15P | RS

uk.rs-online.com

Each device needs a high current gate driver; eg. you could use half of one of these for a single device, or two for a full bridge, though using two in parallel may be needed for such large devices - the one above has a gate capacitance of 7nF, so needs a lot of current to switch quickly; a 3A driver is really the minimum.

https://www.infineon.com/dgdl/Infineon-IR2110-DataSheet-v01_00-EN.pdf?fileId=5546d462533600a4015355c80333167e

You also need a current sense circuit to restrict the PWM duty cycle or kill the gate drive signals if too much current is drawn, to protect everything.
A hall effect current transducer such as this may be appropriate:

LA 100-P | LEM LA Series Current Transformer, 150A Input, 150:1, 50 mArms Output, 12.7 x 7mm Bore, 12 → 15 V | RS

uk.rs-online.com

If you trace back the gate drive circuit in the controller you have, you may be able to a find logic-level PWM signal / signals that can be used to control the new gate drivers?

Start off with a tiny 24V motor while testing things out, and ensure the current limit part works properly, as a fault in the drive circuit or control waveform could otherwise the FETs and/or batteries etc. before you have time to realise anything is wrong..

(There is an old saying about transistors being created to protect fuses - no standard fuse will help a transistor under fault conditions. There are semiconductor fuses available, but 100A+ ones start at around £25 [plus a holder], more expensive than the power FET!)

20-001-04/125A | SIBA 125A NH Fuse, NH00, 500V ac | RS

uk.rs-online.com

 

[rjenkinsgb]

Or just buy something like this and hope for the best?

MAX 100A PWM DC Motor Speed Controller CW CCW Reversible Switches 12V/24V/48V UK | eBay

Maximum current: 100A. Frequency: 15 kHz. Power(Max): 300W. Color: Silver. Sporting Goods. Quantity: 1 Pc.

www.ebay.co.uk

 

[Nigel Goodwin]

Sorry. You can't use a triac for DC. At least not if you want to be able to turn it off.

Triacs are latching devices and keep conducting as long as the current through them is above their holding current. When used with AC, that happens with each zero crossing, but with DC, it doesn't happen unless something else breaks the current.

Well, to be fair, you can - but you wouldn't, as a triac is bi-directional - however, you could (and very possibly would) use a thyristor (one half of a triac) for DC motor control, and that's what used to be used for fork lift trucks etc, anything with very high current DC motors.

Using thyristors for DC is simple and well proven over many decades - you just use another thyristor, and a capacitor, to turn the first one off.

 

[TFC]

Thank You rjenkinsgb and nigel. so happy You have given me something to use. Maybe my high current switch is a Thyristor "(how can I tell?)"
It does switch on and off fast.
rjenkinsgb I am going to look up all this info you have given me so I can understand it before I post again. As I am only an electrician and have no real understanding of electronics your help is much appreciated.
Thanks again
Theo

 

[Nigel Goodwin]

Thank You rjenkinsgb and nigel. so happy You have given me something to use. Maybe my high current switch is a Thyristor "(how can I tell?)"

A thyristor would need extra circuitry in order to switch off, it couldn't just be 'bunged in' in the hope it worked.

Presumably your device has a number on it?, and what did you buy it as?.

 

[shortbus=]

A thyristor would need extra circuitry in order to switch off,

And to my knowledge it would either be on or off. It wouldn't work to be a throttle or work with one.

 

[rjenkinsgb]

And to my knowledge it would either be on or off. It wouldn't work to be a throttle or work with one.

As Nigel says, it is technically possible - but more expensive and more complex than using a suitable power MOSFET for something like this.
Not a practical solution for this application.

A big thyristor is more expensive than the FET, plus you need to bypass the current for something like 120 - 250uS (for the 100A+ rated examples I looked at) for it to turn off each cycle. PWM is possible, but at rather low frequencies.
Very slow and over-complex - and don't even think about a full H-Bridge!

Info:

SCR Turn Off Commutation Circuits

If an SCR is forward-biased and a gate signal is applied, the device turns on. However, once the anode current IA is above the holding current,

www.daenotes.com

Vishay VS-111RKI120PBF, Thyristor 1200V, 110A 120mA | RS

uk.rs-online.com

 

[TFC]

Wow you guys. I think I understand a small part of what you have sent me.

So an FET, IGBT and MOSFET are all high current switches if I understand correctly.
The IR2110 is the interface between my controller and the MOSFET switch.
The LA 100-P / LEM LA is a protection device.

The LA100----- sounds like a great Idea. do I run the battery cable through the bore hole and if a high current is detected the LA100---- will switch something off? MAYBE a solenoid? via the pins on the LA100 ---- device

Maybe the High current switch I have is a MOSFET or IGBT as it does turn off and on with my controller.
What I will do is draw (in my electrician hand writing ) a picture of what I have done so you may be able to show me where to go from here.
I love the idea of the LA100 ----- protection device.
Theo