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jsantala
04 March 2014, 0401
My AXE7245 seems to have a frame leak. If I connect Throttle 2 to car chassis, I get full pack voltage between chassis ground and pack. A bug, a feature or unheard of? I've sent an email to AllTrax, but I though I'd ask you guys too if you've had similar issues.

The reason why I have Throttle 2 connected to chassis ground is because I'm using original carburetor TPS as throttle input and it uses +5V from the vehicle, which obviously has it's negative in the car chassis.

Edit: It may not be a leak. It may be a feature. Not a very desirable though. Stay tuned.

Throttle 1 = pin 2
Throttle 2 = pin 3

frodus
04 March 2014, 1204
The throttle is not isolated and actually references ground internally. Use a dedicated 5v supply for the tps that references pack negative and don't ground it to chassis. That way you keep isolation from the Chassis.

Look up hall effect alltrax and there should be a discussion or two.

jsantala
04 March 2014, 2252
Thanks, frodus. AllTrax also replied confirming this. It's a shame they done such a thing. I'll go check those previous discussions.

frodus
05 March 2014, 0044
Yeah, no problem!

I don't think these golf cart controller manufacturers think isolation is a huge concern, especially at Low voltages like this. It becomes huge when youre talking several hundred volts. If it were that high, you would likely have fried something.

So a small 5v isolated supply should fix it no problem. If you could, post back with your solution for others. Using a tps is a great idea.

jsantala
05 March 2014, 0810
Yeah, if were doing a modern motorcycle with injection it will probably have a very similar TPS that you could steal the throttle signal from without touching anything else to keep throttle feeling exactly as it was. You'll just need to have custom throttle curve done. The guys at http://www.picoamps.de/automotive/en/service_en.htm did one for me.

I put one of these on order, hopefully it will do the trick and give me an isolated +5V to feed the TPS with:

http://www.amazon.de/dp/B00D1GQA5O/ref=pe_386171_38075861_TE_item

frodus
05 March 2014, 1013
Looks good! doesn't need to be isolated.... just do not ground it to frame. Looks like a good solution for a tps and alltrax... And sealed!

If you don't mind me asking. How much for a modified throttle curve?

jsantala
05 March 2014, 1200
They charge about 20€ plus VAT. Very reasonable, I think.

That cheap 12V to 5V may still leak that nasty battery negative back into the frame, since it will be connected to frame on the 12V side, but we'll see. If that doesn't work the picoamps guys suggested putting a converter into the pack voltage, which wouldn't have this issue, but 50-90VDC to 5V converters don't exactly grow on trees...

bjn
05 March 2014, 1208
It may work with a standard 110-230VAC to 5VDC adapter. They are generally of the flyback topology, which makes them able to operate at very low input voltages. If it will work in practice depends on whether the manufacturer bothered to put a low input voltage limit in the circuit.

jsantala
05 March 2014, 1227
bjn, I thought of that too. I've used a 12V power brick in the motorcycle as a DC/DC converter and it works. I'm just a little concerned that when the pack gets near empty (it can go as low as 50 volts if one really pushes it), it won't be nice if the converter then gives up and I lose throttle completely.

bjn
05 March 2014, 1341
I had one which shut down at about 50V. Then I modified the circuit to bypass the low voltage limit, and had it working down to about 24V, but the output was unstable below 35V.

frodus
05 March 2014, 1452
Oh... Crap. I didn't see it was 12 to 5v. Yeah.... It's not isolated so the trouble remains. Those converters have a common ground between n and out. So even if your 12 dc-dc is isolated and you hook a 12v to 5v dc-dc to it, you break that isolation of the 12v.

Let me look, but I may have a dc-dc that at least puts out 12v with a 72v nominal input.

I've found dc-dcs for quite a few people here... So lemme see what I can find. If I have to buy it and ship it to you I don't mind.

jsantala
20 March 2014, 1021
The cheap 12V to 5V I ordered wasn't isolated as I figured. I'll need to step down from the pack voltage, either directly or first 12V and then 5V. Isolation doesn't matter there, because I won't have to ground it to chassis, so it can float.