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Help with 3 wire generator start circuit?
By Volvo farmer, Section Controls Posted on Tue Sep 12, 2006 at 06:45:52 PM MST
Time delay relays?

Here's what I need to do. My inverter has an AUX output that I can program to start the generator. It will give a 12V signal, enough to power a relay for this task.
My generator is an Onan Emerald LPG with three wire start. I found the proper wires on the pigtail to remote start it. Basically, there's a common that rocks onto a start contact one way and a stop contact the other way. It has a nifty circuit board that drops the starter out once it's running. Basically you can keep the start circuit closed indefinitely and it doesn't affect the operation. Same thing with the stop switch.
So I wired a 12V DPST relay in to this circuit and everything worked great. Only problem was my battery was dead next morning because leaving the stop circuit closed draws on the order of 1/2A. So I need some sort of time delay relay. I'd like to put one on the start and stop side. The start side is pretty easy to figure out if I could find the right kind of relay. The 12V signal appears and the relay opens ten seconds later. The stop side is a little more troublesome, I need a circuit that closes a relay for ten seconds when the inverter drops the 12V signal.
There's off the shelf controls that will do this for me but they're about $200 and have a bunch of features I don't need. I know there's a bunch of smart electronics guys around here, could anyone help me out? I'm not very good at designing circuits, like around a timer chip or something but I can solder and I can order parts. Anyone know where I can get a 12V relay that will open and stop drawing power after ten to thirty seconds?

Help with 3 wire generator start circuit? | 19 comments (19 topical)

Re: Help with 3 wire generator start circuit? (3.00 / 0) (#1)
by AbyssUnderground on Tue Sep 12, 2006 at 02:08:51 PM MST

You probably wont get a prebuild relay that will do that but you could probably build a small circuit to do it.

http://www.repowered.co.uk - My Renewable Energy site.
msn[at]m3ezw.co.uk - my msn if you want a chat.

Re: Help with 3 wire generator start circuit? (3.00 / 0) (#2)
by ghurd on Tue Sep 12, 2006 at 02:30:55 PM MST

Hi Volvo Farmer,
You may be able to hook it up with a couple relays, series/ paralleled, and a
"Delay On Release Time Delay Relay".
NTE has some, others make them less expensive.
G-
Ghurd.info

Re: Help with 3 wire generator start circuit? (3.00 / 0) (#8)
by ghurd on Wed Sep 13, 2006 at 08:37:11 AM MST

This is what I had in mind. Not sure if it helps.
Using the opposite type relay, or switching a couple connections will make it do other things. 10 and 60 seconds depend on the realy, but you know what I mean.
Some cars have TD relays for the dome light, ot to operate windows for a short time after the car is turned off.

Ghurd.info
[ Parent ]

Re: Help with 3 wire generator start circuit? (3.00 / 0) (#9)
by Volvo farmer on Wed Sep 13, 2006 at 02:48:59 PM MST

Thanks for drawing that out. I studied it for a while and am not sure it will do what I want, I'll look at it some more when I get my time delay relays in the mail. I was thinking of using the primary relay (the one I already have) to drive a couple of time delay relays which would be powered by the generator starting battery, and would open and close the start and stop switch. I don't know how to make a circuit like the one you drew up without pencil and paper though :-)

Volvo Farmer

[ Parent ]

Re: Help with 3 wire generator start circuit? (3.00 / 0) (#12)
by ghurd on Thu Sep 14, 2006 at 08:58:48 AM MST

The wire leaving the first relay can be switched to the other terminal, and the Vout will be oposite.

BTW, GE(?) makes a tiny fan motor for 'fridges that is an ECM.
If, by chance, you want to part with a used (meaning cheap) one... Yahoo ghurd1
G-
Ghurd.info
[ Parent ]

Re: Help with 3 wire generator start circuit? (3.00 / 0) (#3)
by BigBreaker on Tue Sep 12, 2006 at 03:25:36 PM MST

You need some sort of feedback from the generator to interrupt the current from the outback. I'd cycle that control circuit several times (start and stop the gen). Use a multimeter to track down a control signal that toggles when the starter disengages - the signal that the generator is up and running. If you simply switch off the AUX signal after some period of time, you run the risk that the signal was missed and the generator will never start. True feedback is best for that reason. A timing cutoff might still be worth while to avoid blowing through your batteries if the generator fails and the starter control signal never toggles.

Anyway, take the control signal and feed it into a transistor or FET placed between the AUX output and the relay. Use it to choke off the current from the outback. If you use a FET and it keeps blowing out you may want to drop a cap and resistor from the gate to ground. The control board on the gen might see some ugly spikes from the generator, either induced or something getting through the power supply. A cap/res to ground will protect it.

Re: Help with 3 wire generator start circuit? (3.00 / 0) (#4)
by RP on Tue Sep 12, 2006 at 06:10:18 PM MST

It sounds like you need the "start" relay to stay on (or at least that it won't hurt since the generator will be running) but you need the stop relay to be a 10 second pulse type. If that's the case you can do this with your junk box.

Use a double throw relay for the start contactor. Connect the normally closed contact on this relay through about 1000mfd of capacitance to the coil of another relay (the stop relay) and parallel the capacitor with a resistor of about 10,000 ohms or so.

When the start relay turns off it will send 12volts through the capacitor to the stop relay. The capacitor will conduct for a short time (3-10 seconds) while it charges up. Once it's charged it will stop conducting and the only current passed to the relay will be through the resistor (0.0012 amps). When the invertor calls for a start again, it will unpower the stop relay and the capacitor will discharge through the resistor and be ready to go again.

Hope this helps

Re: Help with 3 wire generator start circuit? (3.00 / 0) (#5)
by Volvo farmer on Tue Sep 12, 2006 at 08:02:22 PM MST

Ooooh, That sounds like it might work and is exactly the kind of solution I was looking for! Thanks for that. I've got a junk box and will give it a try. I'll let you know if it works.

Volvo Farmer

[ Parent ]

Re: Help with 3 wire generator start circuit? (3.00 / 0) (#6)
by RP on Tue Sep 12, 2006 at 08:17:21 PM MST

Depending on the resistance of the "stop" relay coil, you may need to experiment with the value of the capacitor and resistor.

Also, if you want, you can fancy it up a bit by using a double pole, double throw relay for the "start" relay and using the second set of contacts to discharge the capacitor (through a ~50 ohm resistor). This would allow you to almost immediately operate the "stop" relay without waiting for it to discharge through its own shunt resistor.

[ Parent ]

Re: Help with 3 wire generator start circuit? (3.00 / 0) (#7)
by fishfarm on Wed Sep 13, 2006 at 07:38:04 AM MST

"Anyone know where I can get a 12V relay that will open and stop drawing power after ten to thirty seconds?"

I was looking at one of these to control the glow plug operation of my diesel generator.

http://www.elkproducts.com/products/elk-960.htm

The cheapest I could find:

http://www.cctvonlinestore.com/product_info.php?cPath=1007_18&products_id=453057106

Re: Help with 3 wire generator start circuit? (3.00 / 0) (#10)
by Volvo farmer on Wed Sep 13, 2006 at 02:53:33 PM MST

Great! I ordered two! If they don't work out, I'll try the capacitor and resistor thing, I've only got $35 in parts in it anyway. Hehe, If I get this to work, there might be a market for a simple generator starter for Outback inverters. The cheapest thing I found was made by Xantrex and was about $175. It had a bunch of features like low battery start, etc which the Outback already does.

Volvo Farmer

[ Parent ]

Re: Help with 3 wire generator start circuit? (3.00 / 0) (#11)
by fishfarm on Thu Sep 14, 2006 at 07:34:10 AM MST

I forgot to give you the link to the users manual. I assume there will be one included with the timer, but it's nice to have a larger print if it's one of those "folded to the size of a postage stamp" paper manuals.

http://www.smarthome.com/manuals/7279.pdf

[ Parent ]

Re: Help with 3 wire generator start circuit? (3.00 / 0) (#13)
by dog55 on Thu Feb 21, 2008 at 03:49:28 AM MST

Hi volvo farmer

have the same type setup as you dissus

saw your pic with the two 960's in the case but i do not understand how they are connected to the system.

is there a diagrame better showing the wiring?

I do not see any wire on the trigger points on the relays

regards dog55

[ Parent ]

Re: Help with 3 wire generator start circuit? (3.00 / 0) (#14)
by Volvo farmer on Thu Feb 21, 2008 at 04:47:52 PM MST

Sorry, didn't see your post.

I haven't used my remote start in a while, changed generators. It's still all hooked up though. I'll go see what I can when I get home this evening and try to help.

Volvo Farmer

[ Parent ]

Re: Help with 3 wire generator start circuit? (3.00 / 0) (#15)
by Volvo farmer on Thu Feb 21, 2008 at 08:04:06 PM MST

You know, I'm trying to remember how I did this and I'm sorry, I just sat down in the power shed with some wire, some tools and the manual and figured it out as I went. If you saw my plastic box, you found the diary about this project.

I just am not motivated enough to go out there and look at things and make a wiring diagram and upload it onto the internet, but I'll try to explain in words what I did.

So my Outback has an Aux feature which turns a relay on and off. When the relay is closed, 12V goes to the timers and the ELK closes contacts for ten seconds. This is wired into the nine pin connector on the Onan on the same two wires which would close when the start button is pushed.

When the relay via the aux function goes open, the other timer senses the lack of 12V and closes the two wires on the Onan nine-pin connector which correspond to the stop button for ten seconds.

Hope that helps.

Volvo Farmer

[ Parent ]

Re: Help with 3 wire generator start circuit? (3.00 / 0) (#17)
by dog55 on Sat Feb 23, 2008 at 05:22:38 PM MST

Thanks Volvo

Guess i am just a few years behind you.

Read the part on the ELK owners manual that says the relay fires once upon the application of 12 volts , guess this will be my trigger. So I will take this info and Rube Goldburb this up, in Canada there is not too much solar at this tme of the year.

Thanks for your help and the good info Volvo.

Regards Dog55

[ Parent ]

Re: Help with 3 wire generator start circuit? (3.00 / 0) (#16)
by rossw on Fri Feb 22, 2008 at 01:23:43 AM MST

I think I may have a very similar it not identical unit:

(Click image for larger view)

While I built a complete microcontroller for my main genset, the Onan worked fine during construction.

Mine has a centre-off spring-return toggle switch for start/stop, so I'm guessing its similar to yours.

Something you could try (it'd be REAL cheap), would be to use a SMALL relay for the "Stop" function, with a LARGE electrolytic capacitor in series with its coil. I'm guessing something like a 4,700uF electro, and a relay that only takes a few milliamps coil current.

This will let the relay pull in immediately it gets the "STOP" signal, but will only stay pulled in until the capacitor charges enough to have its charge current less than the relays hold-in current.

Will draw a circuit if you need, but sure you can figure out from that!

You could possibly even use the same cap so the start relay only runs for a few seconds too, reducing waste power. As long as the delays are long enough to do the job of course!

One word of caution though: how are you turning on and off the gas supply?
I found that if the builders left the gas bottles on for a week, they'd be empty when I got to them. I guess the regulator "leaks" a little bit.

Re: Help with 3 wire generator start circuit? (3.00 / 0) (#18)
by Volvo farmer on Sat Feb 23, 2008 at 08:24:25 PM MST

If you are replying to me, I solved my problem over a year ago, but thanks.
http://www.fieldlines.com/story/2006/10/1/02437/5303

My generator is hooked into the 250 gallon tank that supplies the house. It has an electrically operated valve that shuts off the LP gas when not in use.

Volvo Farmer

[ Parent ]

Re: Help with 3 wire generator start circuit? (3.00 / 0) (#19)
by rossw on Sun Feb 24, 2008 at 03:55:42 AM MST

Oh my goodness! I hadn't looked at the date.

Humble apologies!

I likewise have electric valves on both my primary and backup gensets, but sadly not on the onan. 250 gallon is 1100 odd litres - the same size as my propane tank here :)

[ Parent ]

Help with 3 wire generator start circuit? | 19 comments (19 topical)

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