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bdpreece · 05-22-2011, 12:15 AM

Quote:

Originally Posted by RCLImperial

Just a bit of electrical engineering fundamentals.... The resistance quoted is the coil resistance. The power dissipated is equal to voltage squared divided by resistance. At 12 volts, the power dissipated by the 32 ohm coil is 4.5 watts, by the 7.7ohm coil, the power is 18.7 watts.
The contacts that are closed by this coil should dissipate zero watts, unless the contacts are bad.

So would you purchase this relay or the upgraded trombetta with the silver contacts?

RCLImperial · 05-22-2011, 08:51 AM

Quote:

Originally Posted by bdpreece

So would you purchase this relay or the upgraded trombetta with the silver contacts?

Go back and read Moisheh's comments about simply replacing things without knowing what is really going on. This used to be called "easter-egging" by techs in the days of tube electronics. It can get very expensive. You can get a digital voltmeter from Harbor Freight for about $5. Get a couple so you have one with you in the motorhome.
With the trombetta relay closed, measure the voltage drop across the relay. That will tell you whether you have a problem. If the relay is OK, you should see much less than a tenth of a volt.

bdpreece · 05-22-2011, 09:41 AM

I did purchase a new meter and I have isolated the problem to the trombetta. I disconnected the chassis side of the batteries from the trombetta I then measured the voltage between the purple and white wire to show that the 12 volt signal to pick the relay was there. The trombetta is hot to the touch which also shows that it is at least attempting to pick. On the House side of the trombetta I have 12.58 volts. On the chassis side I have less than 1/2 a volt. Sure looks to me like I need a new relay since there should be the same voltage on both sides of the relay when picked.

Now back to my question to RCLImperial. would you purchase this relay or the upgraded trombetta with the silver contacts?

RCLImperial · 05-22-2011, 10:20 AM

Quote:

Originally Posted by bdpreece

I did purchase a new meter and I have isolated the problem to the trombetta. I disconnected the chassis side of the batteries from the trombetta I then measured the voltage between the purple and white wire to show that the 12 volt signal to pick the relay was there. The trombetta is hot to the touch which also shows that it is at least attempting to pick. On the House side of the trombetta I have 12.58 volts. On the chassis side I have less than 1/2 a volt. Sure looks to me like I need a new relay since there should be the same voltage on both sides of the relay when picked.

Now back to my question to RCLImperial. would you purchase this relay or the upgraded trombetta with the silver contacts?

Since the Trombetta is obviously a problem, you do need to replace it. I have the White-Rodgers relay in my coach, and it has been satisfactory in a coach that is 7+ years old. I have an '04 HR Imperial, but the relay is only energized when the engine is running. For maintaining the batteries, I have a Lambert battery maintainer which connects all the batteries when on AC. I suspect that both the Trombetta and the White Rodgers will work for your situation. It may come down to the cost of each. For sure, if you get the Trombetta, you should go for the silver contact version.

RCLImperial · 05-22-2011, 02:39 PM

[QUOTE=bdpreece;860606] On the House side of the trombetta I have 12.58 volts. On the chassis side I have less than 1/2 a volt. Sure looks to me like I need a new relay since there should be the same voltage on both sides of the relay when picked.

Got to thinking about the 1/2 volt on the chassis side of the trombetta relay. Seems to me that the voltage there should be the voltage at the chassis batteries. When the trombetta relay is activated, the house and chassis batteries are tied together. I suggest that you do some more detective work to see what's really going on. There could be a poor connection somewhere in the line that connects the trombetta to the chassis batteries.

RJay · 05-22-2011, 02:43 PM

Quote:

Originally Posted by RCLImperial

Just a bit of electrical engineering fundamentals.... The resistance quoted is the coil resistance. The power dissipated is equal to voltage squared divided by resistance. At 12 volts, the power dissipated by the 32 ohm coil is 4.5 watts, by the 7.7ohm coil, the power is 18.7 watts.
The contacts that are closed by this coil should dissipate zero watts, unless the contacts are bad.

Oh yes fundamentals, except were not talking about fundamental in this case we're talking about principles and laws. I agree that the formula Power=V2/R is correct but the reason why it gives a different answer can be found here.

The law I applied is Joule's Law and its origin and application can be found here.

Conventional wisdom is that as resistance increases for the same amount of current flow the heat dissipated will increase over time. This is certainly understood by every RV'er who has found bad battery connections, or any corroded connection that passes a current. So if we apply conventional wisdom to each formula it should prove the conventional wisdom.

The formula you are applying is Power = V2 / R. As the denominator(R) gets larger the corresponding power gets smaller, going against conventional wisdom. On the other hand, Joule's Law which is P = I2 xR, as R gets larger P becomes larger and conversely as R gets smaller P becomes smaller which follows conventional wisdom.

So your fundamental are good, your application is flawed.

bdpreece · 05-22-2011, 03:06 PM

[QUOTE=RCLImperial;860800]

Quote:

Originally Posted by bdpreece

On the House side of the trombetta I have 12.58 volts. On the chassis side I have less than 1/2 a volt. Sure looks to me like I need a new relay since there should be the same voltage on both sides of the relay when picked.

Got to thinking about the 1/2 volt on the chassis side of the trombetta relay. Seems to me that the voltage there should be the voltage at the chassis batteries. When the trombetta relay is activated, the house and chassis batteries are tied together. I suggest that you do some more detective work to see what's really going on. There could be a poor connection somewhere in the line that connects the trombetta to the chassis batteries.

It was in my original test where I showed 12.58 on the house side and 12.41 on the chassis side. I then disconnected the chassis batteries from the circuit to see if anything was actually passing through the relay and all I got was 1/2 a volt. The 12.41 volts I was reading was the charge in my chassis batteries rather than what was being passed through the relay.

itdave · 05-22-2011, 04:44 PM

Brian,
I think you have correctly identified the problem as being the Trombetta Relay. I have read where people have disassembled the relay and repaired the contacts. This might work as a short term cheap fix but long term I think a new relay with silver contacts is the best answer.

bullydogs1 · 05-23-2011, 04:42 AM

I purchased two things for a total of $90 to make sure the cross charging was working properly..I replaced the trombetta with the upgraded one AND I purchased the new MegaTech upgraded board. This board is programmed a bit better to engage the Trombetta relay which wasn't happening with either house to chassis or chassis to house.. Checked all since then now trombetta is engaging properly..This relay gets a workout so you need the heavy duty one without question. This trombetta is the only way Monaco products cross charge.

Note I read somewhere that 2008 models did not have the megatech board so no cross charging from house to chassis...owners' manual is wrong for that year.

Remember you want the trombetta ending in -020- the 010 is a piece of junk that Monac used to save money.

Bob (WA0MQE) · 05-23-2011, 07:45 AM

Quote:

Rjay: On those meters aren't the "claws" only for 110 Volts AC??.

They also make one that will work with both DC and AC. I have one I purchased at a reasonable price from Sears. I tested it alongside a Fluke that a friend of mine has that he uses at his shop. It tested within a half-amp give or take alongside the Fluke. You could buy a Fluke but the price will be way up there.

bdpreece · 06-13-2011, 05:08 PM

I finally returned home to Oregon and got the heavy duty trombetta replacement. Today I installed the new one so I disassembled the old one just for fun. Even holding the relay picked with my hand I get no continuity between the two power posts. See the attached pictures for why.

Alga Forrest · 08-27-2011, 10:50 PM

Hello Brian,
I assume you had only the trombetta relay to replace, as There have been no further posts for a while. I found out I had a similar problem today. I have a 2009 Knight and in the batt compartment in what Monaco refers to as a "Charging Relay."
It's located on mine just below the j-box, above the batteries. The coil is energized, but one side was 13.6VDC while the other side was only 7VDC. So I will try to locate another one of better quality in the next few days.

rpasetto · 08-28-2011, 07:24 AM

BD, you can call the Monaco hotline, give them your coach #, that may help you locate the BIRD relay, or tell you whether it's there or not. Also Monaco tech support may be able to email you a wiring diagram.

RJay · 08-28-2011, 08:00 AM

Quote:

Originally Posted by Alga Forrest

Hello Brian,
I assume you had only the trombetta relay to replace, as There have been no further posts for a while. I found out I had a similar problem today. I have a 2009 Knight and in the batt compartment in what Monaco refers to as a "Charging Relay."
It's located on mine just below the j-box, above the batteries. The coil is energized, but one side was 13.6VDC while the other side was only 7VDC. So I will try to locate another one of better quality in the next few days.

Hi Alga,
You might want to look at these as a replacement for the trombetta.