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03-28-2012, 09:19 PM
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Join Date: Jan 2005
Location: Weirsdale Fl 97fl (winter) Cherokee, NC (summer)
Posts: 42
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Quote:
Originally Posted by Jetguy
Ive cranked my for up to 30 second s with out any problems on the old system. 
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Yea, I've got the skyview, cranked about 15 seconds 3 times today, no problems.
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03-30-2012, 12:25 PM
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Join Date: Apr 2010
Location: Tucson, AZ
Posts: 461
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A Rotax starts up quickly when you run it frequently. Not so quick when it sat f ro a while or when it's bitter cold. I cranked my older ROtax on the RANS S-12S quite a while in the winter (with the upgraded starter motor that is now standard) before it would roar to life.
Why don't you just measure what the current is that is drawn through the fuse? If the fuse holder pins are somehow accessible, put the amp meter in series and let the current run through the amp meter, then crank and see what it shows ...
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03-30-2012, 04:05 PM
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Join Date: Aug 2010
Location: Marshall TX (KASL)
Posts: 1,783
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UPDATE! This is on the 2A starter fuse blowing problem. In working with Van's, I got out the multimeter. Looks like a bad starter relay and here's why.
First, the starter circuit draws 0.22 amps to power the AV-50000A fan with the spar pins properly in. It would draw a bit more if the spar pin warning light was on. Just useful to know, because these amps are ADDED to whatever it takes to power the starter relay.
Then I did this.
I disconnected the Rotax starter power supply wire from the starter relay. This is so I could do the test without the prop spinning.
Battery is reading 12.5 V.
I put a 3 amp fuse in the starter circuit.
I wired the multimeter, set for 10 amps, in between the male spade plug on the starter relay and the female wiring that connects to it. (I made some scrap 18 gauge extension wires with cheap spade-type lugs to connect up the multimeter.)
I turn the starter switch on.
I immediately get 2.7 amps!!!
No wonder the 2A fuse is blowing.
Several tests of the starter switch give the same result.
As a test, I swap out the 3A fuse for the proper 2A fuse and repeat the test. Sure enough, it blows after about 10 seconds.
So something is up with the relay!
My relay was unmarked. Van's say they come from ROTAX. They are theorizing it is either a bad relay or a 24V relay - since it is only supposed to draw about 1.4 amps.
I measured the OHMS from the tab to the body of the relay. It is 4.6 OHMS.
Per good old V=IR, 12.5 VOLTS divided by 4.6 OHMS = 2.7 AMPS! (I don't remember the formulas to take into account DC through a coil...)
So it seems that the OHMS on the relay should read more like 9 OHMS.
So Vans is checking. If you can conveniently get at your relay, you might want to check it's resistance also.
In thinking about the above, I would think that the 24V relay theory is wrong. A 24V relay with 4.6 OHMS would draw 5.2 amps in a normal condition. That's way high. A 24V relay would seem to need MORE resistance built into the coil than a 12V relay, not less. Oh well...
More when it is concluded...
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03-30-2012, 04:13 PM
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Join Date: Nov 2007
Location: Jesup, Iowa
Posts: 1,657
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Hey Bill - -
I sent you a PM a while back. Did you get it ? ? ( this subject )
John Bender
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04-03-2012, 08:57 AM
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Join Date: Aug 2010
Location: Marshall TX (KASL)
Posts: 1,783
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Final Resolution - Starter Fuse Blowing
Scott at Van's investigated the issue with starter relays they have on hand, supplied by Rotax. The relays (and there has apparently been some sort of unannounced change by Rotax) are like mine, with similar resistance, and do draw well over 2 amps.
Van's is making inquiries to Rotax. They also say "Our engineers have evaluated the circuit and it will handle 3 amps continuously so intermittent starting draws near 3 amps should not cause any problems." So if you have issues, use a 3A fuse."
They also say Auto fuses will function fine. The fuses Van's supplies with the avionics kit (3 amps and above) actually light up when they blow so if you want that type, you can order them from Van's or source them elsewhere.
+++
One other RV-12 owner guy has told me he has a 3A fuse installed since
a similar problem when new and has never blown it.
I understand the Rotax starts so fast - and the fuse seems to take
more than 5 sec to blow - that the problem is rarely encountered.
Note - 2.7 amps for the starter relay, plus .25 amps for the fan
(as tested) is still right at 3 amps.
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04-03-2012, 05:08 PM
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Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,035
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Quote:
Originally Posted by Bill_H
Note - 2.7 amps for the starter relay, plus .25 amps for the fan
(as tested) is still right at 3 amps.
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Bill,
Testing just done on N412RV showed that the start circuit (with control modual fan operating) draws about 2.5 amps. in rush, and then settles at about 2.3 amps after a couple of seconds.
This would be exceptable margin for a 3 amp fuse.
I am wondering if you had a battery charger connected to your battery while you were doing your engine cranking and the amperage testing? If so, this would bump the amperage up enough to be a factor.
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04-03-2012, 07:23 PM
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Join Date: Aug 2010
Location: Marshall TX (KASL)
Posts: 1,783
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No, I always disconnect the battery maintainer before I ever turn on the master switch. Did you happen to measure the OHMS on your relay? As noted, mine was 4.6 ohms.
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04-04-2012, 08:15 AM
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Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,035
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Quote:
Originally Posted by Bill_H
No, I always disconnect the battery maintainer before I ever turn on the master switch. Did you happen to measure the OHMS on your relay? As noted, mine was 4.6 ohms.
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The coil resistance of the relay in N412RV measured 4.7 ohms.
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04-05-2012, 04:29 PM
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Join Date: Apr 2010
Location: Tucson, AZ
Posts: 461
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Quote:
Originally Posted by rvbuilder2002
The coil resistance of the relay in N412RV measured 4.7 ohms.
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So with Ohm's Law this results in:
I = 12V / 4.7Ohms = 2.55A
or with a power supply or a fully charged battery
I = 13.8V / 4.7Ohms = 2.94A
As this is a coil in the circuit you can expect the resistance to be higher when switching on, so the current should always be below 3A, Darn close though, so make sure it's slow fuse or use a fast one at a higher rating, slightly above 3A.
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