Solid state relays

[Burgerman]

http://cgi.ebay.co.uk/SSR-80A-SOLID-STA ... 3a6005cf27

As an emergency cut off in case of roboteq problem!

Can you get 300 or 500 amp ones? Would the odd 300 amp burst kill these 80 amp ones? Never had anything to do with them. They must be high resistance because they come with a heat sink!

I think a switch Or fuse that will blow when a switch is used as a crowbar is easier. I may not bother with either. I can reach the "link" connector on the charge sockets easily enough.

[JoeC]

I wouldn't use a solid state relay for this- the ones you would want are probably a lot more expensive than a mechanical relay or contactor that would be suitable for what you want- either crowbar style or current interrupting. The 80 amp ones are around 5 milliohms, according to specifications I've seen on similar.

The manual disconnect might be good enough if you keep in mind that if something is going REALLY wrong, the cables might start to get a bit toasty when you go to yank them out, and every fraction of a second could matter a great deal when you're trying to kill it.

[Burgerman]

Mmm.. There must be a simple neat easy way to kill the power without it looking like a race car kill switch though.

[JoeC]

Some switches are fairly heavy duty and can be actuated with a cable pull. You could have one of these connected to a suitable relay, and it would be easy enough to rig a pull cable that is hard to accidentally pull and wouldn't look like much. Can you picture that?

[Burgerman]

I can.

I can also remember running a customer/freinds rather over powered competition drag bike once with a drag chute on a similar pull handle! That may not be needed though! The idea being that if it ever got out of shape at silly speeds it would straighten it up. Fortunately I never had to try it.

[Ashley G]

Just been battling the pc again (thanks MicroSnot !) so not really got my thinking-head on straight but ....

John, I don't think I'd rely on being able to snatch the "link" connector out, in the event that the Roboteq burps. You could conceivably be hanging out the wrong side of the chair by then, as it swerves into a road, or something.

Hardly satisfactory, I know but, if all else fails, I'd even think of installing a "Dead Man's switch" before I'd rely on access to the links. Just something you'd have to keep pressed, either in your fist or tucked under your arm or whatever .... anything which would truly be quick to use in such an emergency ?

Ashley

[Burgerman]

I think there are a lot of possible solutions. But I really want something neat, small and just a resettable button or something just behind the joystick as a just in case stop button.

[JoeC]

I think even more importantly I would try not to let the Roboteq ever fail like that. The main failure mode that we're talking about is Mosfet failure, which is the result of bad wiring and pushing the controller to its electrical limits of voltage and current.

The way I'd minimize chance of failure would be to stick with 36 volts, and limit current to something more conservative like 120 amps. I don't think you'll miss the last 30 amps unless you're in deep soft terrain, and the more headroom you give the thing the less chance it will fail. The other thing to do is to be careful with wiring. Keep lengths short, twist conductor pairs, don't run signal close to power. Ground pins that should be grounded, and do everything by the book.

The power and control that comes from even 100 amps from both motors that doesn't fade at all until a jogging pace is a fairly useful thing- even for a large guy such as yourself.

Another possibility if you're worried about more than just mosfet failure would be to rig an E-stop button as a digital input to the controller. That's configurable, and will immediately kill the output when activated. That would be easy enough to put near the joystick, and would be useful if something went wrong with your joystick trim resistors, or you had some other input error.

[LROBBINS]

I think that your safest bet is a crowbar arrangement as someone else suggested earlier. A switch just downstream of the main fuse that creates a dead short would cause the fuse to blow cutting off all power.

[Burgerman]

I think I will do both. The inputs (all - rc and joystick) are limited at the ends of travel in case a wire fails, or interference or other input faliure etc. That will just stop it. As will a digital input on a switch.

[LROBBINS]

Stop via the Roboteq is for "normal" operation - a crowbar is "in case the Roboteq fries ON"

[Burgerman]

Yes I realise that. How likely IS that to ACTUALLY happen? I might email them...

[JoeC]

Emailing them won't help a lot. They're in the US so they'll cover their bases and say "It's not likely to happen, but there's no guarantee it won't!"

You can minimize the factors that would cause it, and have a solid backup plan in case it does happen, but you'll never get them to say anything other than generalized pointers to help avoid it to some extent.

One thing to bear in mind is that doing a hard cut on the battery line while the motors are under power can be quite bad for the controller. Hit the emergency cutoff often enough and at speed, and my understanding is that you'll be increasing the odds that the controller really WILL fail.

[Burgerman]

Theres a bit in the manual explaining that that can be damaging since power generated by motors has nowhere to go. Easily cured by fitting a couple of big diodes across the switch. That way it can still dump power into the bateries but no battery power can get to the controller when you hit the disconnect. So that shouldnt be a problem.

[Burgerman]

I WANT the 150 amps per channel so wont turn that down.

As I see it with 120 amps per channel it will accelerate the same (or better) than the 8.5 rnet powered groove does. But continue accelerating that hard for longer. Especially as I have huge cables and better batteries...

And at 150 amps it will be about 25 percent better than a stock groove for torque (which was pretty good anyway and about 90 percent of what my 6mph chars do) but due to the 36v will accelerate harder and for longer to a higher speed before the amps drop away. So it should leave my old chairs for dead until the batteries die about 5 miles down the road!

[Lord Chatterley]

These may be able to suggest something if you email them-

http://www.keepitcleanwiring.com/search/KILL+SWITCH

[I was looking at their LED tape!]

[Red Dragon]

There is a breaker as you are looking for.
it Is large and has the option to connect it to a small switch which is what you want.
It can also be wireless but it is unnecessary.

http://bepmarine.com/media/product/pro4cc5ee3af0ef3.pdf

http://bepmarine.com/home-mainmenu-8/pr ... ch-500amps

[Burgerman]

Yes planning on usung something similar (but abit smaller) like a starter relay. They can be normally closed or open (contacts both ends). So a tiny latched switch would operate the solenoid.