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Replacement over voltage relay recommendation

L

lowerchena

FRIEND
Fairbanks, AK
I have a Denso CAM 040 Alternator in my PA-18 that was intermittently failing to provide power but has now stopped completely. After troubleshooting the wiring system, master switch, OV breaker, Alternator Field switch, etc., it looks like the Alcor OV-12 over voltage relay is bad. The over voltage relay is not providing power to the alternator field wire which stops the alternator from producing power. I bypassed the relay and the alternator started producing power just fine.

I'm planning on replacing the Alcor with a Lamar OS60. Looking for comments or other recommendations as well.

Jeff
 
Thanks for the info. I have a field approval for the Denso. The paperwork only states that a OV relay needs to be installed, type is not specified.

Jeff
 
what was the OUTPUT voltage when you bypassed over volt relay? it may have been working properly.... don't let the smoke out of your electronics.....
 
The Denso that we sell 0760 has the regulator and over voltage relay inside it so it doesn't require a external regulator or over voltage relay. Don't know if that helps or not. Bill
 
stoddard said:
The Denso that we sell 0760 has the regulator and over voltage relay inside it so it doesn't require a external regulator or over voltage relay. Don't know if that helps or not. Bill
Click to expand...

You know, that's interesting. According to the notes I have included with the field approval paperwork (I bought the cub a couple years ago, Denso installed in 2010), the CAM 040AD alternator is an internally regulated alternator (which I already knew), and also, in case of an internal failure resulting in an over voltage, the alternator is designed to shut itself down. Note, I do have the warning light installed which lights up when the alternator field switch is off, i.e. no field wire voltage supplied, or the alternator has shut itself down (haven't experienced and hope not to).

So perhaps I can just bypass, and remove, the external over voltage relay?

Jeff
 
I think you better try that before spending any more money and time. Me thinks you may have conflicts with too many regulators. Maybe Wire Weenie can help. Bill
 
''''IF'''' you can verify that this alternator has an internal over voltage sensing/cutoff circuit, then, functionally, you shouldn't need an external over voltage cutoff relay. It would just be redundant. If you decide that you need to re install a new one, look at the one used by Cessna.

Either route you choose, for the first few flights, use a digital voltmeter to monitor the voltage at the main bus. You can use the one in the panel (if installed) or just clip a hand held meter to the main bus. You want to make sure that the voltage remains close to 14.2. Couple of tens either way is no problem but you need to catch any over voltage condition immediately. If you make a few flights with stable voltage then the original problem was probably confined to the original over voltage cutoff.

Web
 
Thanks for all the insight. I bypassed the old OV relay. The relay had two field wires, one to my master DPST and one to the alternator. I simply jumpered those two together. A short run up but saw 14.3 to 14.4 on the voltage readout on my cheapo 12v usb adapter. Perhaps not a reliable voltage monitor but it seems to work fairly well so far. Definitely let me know (visual and audible) when my alternator wasn’t providing a charge. I recently had an EI FP-5L installed so this has me thinking I should add the voltage AUX function, albeit a bit pricey.

Jeff
 
Jeff if you have a GPS in your plane there is also a field on one of the pages you can set up a an alert for voltage values. It also reads current voltage. Those over-voltage relays are Infamous for going out and or intermittent. They act like brushes going out. Not saying this is right but I did run my over-voltage bypassed for about 10 years on my Alcor installation.
 
AkPA/18 said:
Jeff if you have a GPS in your plane there is also a field on one of the pages you can set up a an alert for voltage values. It also reads current voltage. Those over-voltage relays are Infamous for going out and or intermittent. They act like brushes going out. Not saying this is right but I did run my over-voltage bypassed for about 10 years on my Alcor installation.
Click to expand...

Thanks, I assume you mean a fixed GPS rather than a portable set up. For now I only a have a Garmin Aera 660 and ForeFlight.

I'll be looking at installing a new OV relay at some point. A minor expense for added safety and peace of mind.

Jeff
 
Probably the right way of doing it. The screen that has the sunrise sunset time of day information on it. You can change one of the fields to read voltage. I thought it was on all the Garmin GPS it is on my 296.
 
AkPA/18 said:
Probably the right way of doing it. The screen that has the sunrise sunset time of day information on it. You can change one of the fields to read voltage. I thought it was on all the Garmin GPS it is on my 296.
Click to expand...

Hmm, didn't notice that option. It's not showing on my 660 as a field option here at home but it does list it in the manual. Probably isn't available when not on system power. Will check it when I'm at the cub.

Thanks!

Jeff
 
lowerchena said:
Hmm, didn't notice that option. It's not showing on my 660 as a field option here at home but it does list it in the manual. Probably isn't available when not on system power. Will check it when I'm at the cub.
Click to expand...

Well, not there when powered from cub. Will need to contact Garmin and see why.
 
Last edited:
lowerchena said:
Well, not there when powered from cub. Will need to contact Garmin and see why.
Click to expand...

As a follow-up, I received a response from Garmin and they removed the ability to add external voltage as a data field option. I had an earlier manual when it was supported. :(
 
Here is what Cub Crafters uses on the Carbon Cubs.
9107.jpeg
9109.jpeg
 

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I have a friend I fly with that has a Carbon Cub and his alternator has been going off line. He replaced the alternator and no change. His old alternator tested good at an alternator shop. I told him the investigate how Cub Crafters deals with over voltage and check that. He texted me those pictures and said there is a service document dealing with it. I have not had time to look at the schematic or service document yet but he texted me those pictures. I will look it up this weekend. If I had a field approval and needed over voltage protection I would go with this.
http://www.bandc.aero/over-voltageprotectionmodule.aspx other useful parts here. http://www.bandc.aero/alternator-system-accessories.aspx
 
Not a fan of crowbars in aircraft systems. A crowbar works by sensing a condition out of spec, in this case over voltage. It then shorts itself directly to ground causing the circuit breaker to pop. The problem is that MANY circuit breakers in aircraft have issues such as old, corrosion, wrong size, etc. In those cases, when the crowbar shorts and the breaker does not trip, you're left with smoking wires. If you have a system with crowbar over voltage protection, when is the last time you performed the test procedure?

This is why I mentioned the Cessna over voltage module. When it senses over voltage it simply opens the circuit just like an 'off' switch.

Web
 
BEEBA62E-F03E-4C16-BFBC-09416B383BB4.jpegFDB02B57-FC70-4A96-AC7A-01C83EDBF328.jpegThe Denso installation paperwork. Read alternator characteristics and see block diagram...No overvolt relay needed...
 

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I talked to the previous owner that had the Denso installed and he said he decided to leave the existing over voltage relay in place rather than remove it.
 
lowerchena said:
I talked to the previous owner that had the Denso installed and he said he decided to leave the existing over voltage relay in place rather than remove it.
Click to expand...

If you are satisfied that there is a safe overvoltage protective circuit built in, then you can just remove the extra OV relay. Sounds like it's not required for this installation and if OV protection is built in, then it's a redundant piece and not useful.

Web
 
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