Yet another solenoid bites the dust! - Page 5

MrTransistor · 11-09-2008, 06:51 PM

Hello hdvectra,

John hit the nail on the head with the ˜wonky contacts'. Having not used the engine for a while, the contacts will develop a very thin oxide coating that acts as an insulator. The first time your coach was fired up, the contactor pulled in but didn't tie the battery banks together because of the oxide coating. Exercising the battery boost switch (with engine off) a few times causes the contacts to make and break and will ˜punch' through the oxide layer and make contact as designed. That's why silver contacts are better. Not that they don't develop an oxide coating but being softer, the mechanical force of the contacts closing every time is enough to break the oxide layer. All relays and contactors should use silver contacts! But then there is the price.

This procedure (getting the tie contactor working) ultimately is much safer than putting a jumper between the battery banks. Depending on the state of charge of each bank and the current available from the engine alternator, there could be a pretty high current flowing in your jumper. If the size of wire is not adequate for this current, then the wire could overheat. What I do is, just after engine start and while I'm waiting for the jacks to retract and air bags to inflate, go to the One Place and check that I have better than 13.1 Volts on both the coach and chassis batteries. That tells me the tie contactor did connect the banks together. If there is say 12.8 Volts on the house batteries and 13.4 Volts on the chassis batteries, then I know there was a contact fault on the tie contactor. If that happens, shut down the engine, press and release the Battery Boost Switch a half dozen times, then fire it up again. This only seems to happen if we've been sitting for an extended period. Once I have cleared the contacts, it will work properly for the entire trip.

I would suggest that you install something like a Xantrex Echo Charge. That way you don't need to run the engine just to charge the chassis batteries and this is much safer than using a jumper. Keeps the banks isolated as well. A jumper could mean that all your batteries go dead instead of just the house or the chassis in case of a fault.

PeteB · 11-10-2008, 04:21 AM

If one decides to use resistors instead of diodes, is it necessary to protect against back EMF?

Thanks,
Pete

John_Canfield · 11-10-2008, 05:01 AM

Certainly wouldn't be a bad idea to use one across the coil if you can. The solenoid doesn't come from the factory with one, and I'm thinking modern electronics do a much better job at clamping spikes in their power source than electronics of many years ago.

So - my opinion is great if you can install one, okay if you can't.

PeteB · 11-10-2008, 09:33 AM

Thanks John,

One more question. How do you hook up a resistor across the terminals? I assume that there is no + and - like on a diode so do you just hook up one end to the + post and the - to the other?

Thamks,
Pete

NoMoreAZ · 11-10-2008, 12:01 PM

PeteB,

Attach resistor either end to either terminal. See my post on previous page as to what type of connectors I used when I installed the diodes. Leave some room around resistor(s) so it (they can get some air flow around them.

PeteB · 11-10-2008, 12:43 PM

Thanks,
This will be one of my next projects.

Pete

rdalcanto · 11-10-2008, 02:13 PM

NoMoreAz,
Can you please post a picture of a Diode hooked up backwards for those of us with little electrical experience? (From where to where exactly) Thanks!

John_Canfield · 11-10-2008, 07:06 PM

Two different scenarios here. Scenario one: Dropping voltage so the coil operates at a lower voltage and doesn't get as hot when operated. You can use diodes in series (I think somebody used three of them) or a resistor (or two/three resistors depending on their value.) I think this has been well detailed in other posts .

Scenario two: A coil can create a voltage spike on the 12V supply (back EMF) when voltage is applied and removed to the coil which could damage some sensitive electronics. The common fix for this is a diode connected directly across the coil connections. The diode will safely short out any of these voltage transients. I can't remember for the life of me if the anode or cathode of the diode goes to positive or negative of the coil supply.

I seriously doubt if this is necessary since the battery bank also acts like a giant capacitor to minimize any of these transients. Relays sometimes have a diode across the coil in electronic equipment - just depends on the design of the equipment. Relays used in digital equipment would most certainly have a coil diode since the logic circuits would be extremely sensitive to any spikes.

Maybe Mark (Mr. Transistor) will have more to add.

MrTransistor · 11-10-2008, 09:56 PM

Hi All,

I'm here, I think... Attach the cathode (the end with the band) to the plus (+) side of the contactor's coil (hopefully a red wire). Attach the anode (the end without the band) to the ground (-) side of the contactor's coil. If you hook it up backwards, you'll know right away because it will smoke the first time power is applied. The rating on the diode isn't too critical since it only passes current when power is removed form the contactor and then for only a brief time of a few milliseconds. A good diode for this purpose would be a 1N4007 that you can get at a Radio Shack. If the diode doesn't have a band but instead has a symbol that resembles and arrowhead (kind of) with a line crossways at the tip, the arrow points toward the cathode.

If you don't know which wire of the contactor has the +12 Volts on it, use a digital volt meter with the leads plugged into it red to red, and black to black. Have someone press the Boost switch as you observe the contactor. With the contactor energized, place the two leads of the meter to the terminals of the contactor. If the red lead has the +12 Volts, the reading on the meter will be positive (12). If the red lead is on ground and the black lead is on the +12 Volts then the meter will read a negative 12 Volts (-12).

In a straight diode, current is allowed to flow from the cathode side to the anode side and is blocked from passing current in the other direction. When current does flow from cathode to anode, the diode is said to be forward biased and will drop a voltage. Two or more diodes can be used in series to provide a reduction in applied voltage to the contactor. Precise by no means but the rule of thumb for silicon diodes like the 1N4007 is .8 Volts of drop per diode. But don't use 1N4007s for this purpose. They can only handle 1 Amp. of continuous current and the contactor could very well have more than that.

Generally speaking, all this diode does is prevent arcing on the Boost switch or engine relay contacts as they are trying to turn the contactor off. That's why coach manufacturers and Trombetta don't install them at the factory, saves money.

If anyone decides to use diodes to drop the contactors voltage, a good diode choice might be the Radio Shack part number 276-1661 ($2.49). It is a pack of 4ea. 6 Amp. 50 Volt diodes, and they do have a band on the end. One of these will also work across the contactor. Also part numbers 276-1144 ($1.59ea.), 1143 ($1.59ea.), and 1141 ($1.49ea.) will work nicely.

John_Canfield · 11-11-2008, 05:11 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by MrTransistor:
.... If you hook it up backwards, you'll know right away because it will smoke the first time power is applied. ... </div></BLOCKQUOTE>Ha! I've performed that test before!

Winnie generally uses yellow for positive and white for negative, so that will help to figure out the polarity.

Thanks for the component info Mark.

Ready2Travel · 11-11-2008, 05:29 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by MrTransistor:
Hello hdvectra,

John hit the nail on the head with the ˜wonky contacts'. Having not used the engine for a while, the contacts will develop a very thin oxide coating that acts as an insulator. The first time your coach was fired up, the contactor pulled in but didn't tie the battery banks together because of the oxide coating. Exercising the battery boost switch (with engine off) a few times causes the contacts to make and break and will ˜punch' through the oxide layer and make contact as designed. That's why silver contacts are better. Not that they don't develop an oxide coating but being softer, the mechanical force of the contacts closing every time is enough to break the oxide layer. All relays and contactors should use silver contacts! But then there is the price.

This procedure (getting the tie contactor working) ultimately is much safer than putting a jumper between the battery banks. Depending on the state of charge of each bank and the current available from the engine alternator, there could be a pretty high current flowing in your jumper. If the size of wire is not adequate for this current, then the wire could overheat. What I do is, just after engine start and while I'm waiting for the jacks to retract and air bags to inflate, go to the One Place and check that I have better than 13.1 Volts on both the coach and chassis batteries. That tells me the tie contactor did connect the banks together. If there is say 12.8 Volts on the house batteries and 13.4 Volts on the chassis batteries, then I know there was a contact fault on the tie contactor. If that happens, shut down the engine, press and release the Battery Boost Switch a half dozen times, then fire it up again. This only seems to happen if we've been sitting for an extended period. Once I have cleared the contacts, it will work properly for the entire trip.

I would suggest that you install something like a Xantrex Echo Charge. That way you don't need to run the engine just to charge the chassis batteries and this is much safer than using a jumper. Keeps the banks isolated as well. A jumper could mean that all your batteries go dead instead of just the house or the chassis in case of a fault. </div></BLOCKQUOTE>

Made the 500 mile trip home and was able to get the house batteries charging by hitting the boost switch a few times, did not have to use my jumper. Sometimes after shutting down the engine the batteries were charging OK, sometimes not. I hit the boost switch with the engine running, probably should have shut down the engine and hit the boost.

I only use the jumper for a few days every two or three weeks if parked and hooked up to shore power to keep the chassis batteries up so have never risked letting all batteries go dead.

Think I'm going to change out the solenoid before I make my next trip.

PeteB · 11-11-2008, 11:01 AM

Mark,
Thanks for all the info. One last question, if I use the 276-1661 diodes to reduce the contactors voltage, how many are required to lower to the proper voltage?

John - Thanks go to you as well for all the help.

Pete

NoMoreAZ · 11-11-2008, 11:20 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by rdalcanto:
NoMoreAz,
Can you please post a picture of a Diode hooked up backwards for those of us with little electrical experience? (From where to where exactly) Thanks! </div></BLOCKQUOTE>
Here is a link Diodes that shows diodes in pictures and symbols. Further down the page is a diagram showing how to connect a diode across a relay coil (Protection Diode for Relays). 'Bago uses yellow for positive, white for negative in all DC wiring except heavy battery cables.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by PeteB:
Thanks for all the info. One last question, if I use the 276-1661 diodes to reduce the contactors voltage, how many are required to lower to the proper voltage? </div></BLOCKQUOTE>

All silicon diodes are rated to drop .7 Volts. I'm the one who used three of them (see post by SCVJeff on page 7 dated 7/30/08 for the diodes I used). My original post is on page 8, dated 10/22/08.

PeteB · 11-11-2008, 11:45 AM

NoMoreAz,

Thanks for the info. Your link is very helpful.

Pete

MrTransistor · 11-11-2008, 02:09 PM

Later on today, I'll generate a CAD drawing and convert it to .PDF then .JPG and get it posted.

Drawing has been generated and posted, awaiting approval. I'll place it inline tomorrow.

Go here for the full size image if you need to print this. Do a 'Save As' then print from the disk copy.

http://www.irv2.com/photopost/data/5...mbear_copy.jpg

MrTransistor · 11-12-2008, 01:44 PM

Hi PeteB,

I hope this helps to explain the hook-up.

PeteB · 11-12-2008, 05:49 PM

Outstanding!!!!!!

Thanks,
Pete

MrTransistor · 11-12-2008, 10:03 PM

Slightly revised and better picture is coming.

Gee, that was quick!

John_Canfield · 11-13-2008, 04:47 AM

Well done Mark

Ready2Travel · 11-13-2008, 08:52 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Gary CA:
Good discussion/education on solenoids (tie contractor). I contacted Jay at MurCal electronics 800-321-8386. Jay called Trombetta and verified the replacement for the OEM solenoid; that operates at 14V.

I ordered the 114-1211-020 (silver contacts), for $30, and will keep it as a spare.

One would think that with this being such a common problem that Winnebego would have come up with recommendations for a solution by now.

http://www.trombetta.com/dc-contactor-products.cfm?id=8

http://shopping.murcal.com/Welcome </div></BLOCKQUOTE>

This must be a popular part. Just went to the murcal web site to order the silver contact soleniod and it was out of stock.

I'm having a hard time understanding how I was able to get the solenoid to get the house batteries to start charging by hitting the boost switch with the engine running. With the key in the run position 12 volts already should have been going to the coil?

Has anyone ever checked the resistance on the coil of a failed solenoid compared to the new part?

My experience with soleniod activated contacts consists of my time as a mechanic on bowling alley machines when I was going to school in the 60's. In almost all cases failures were pitted contacts caused by arcing and numerious on/off cycles. Rarely did a coil go bad. Most of the time the contacts could be fixed by cleaning the contacts with a file but those contacts were easy to get to.

Will be interesting to see if any failures occur with units installed with resistors to lower the coil voltage. Perhaps these coils are not failing but merely getting weak and not pulling in enough causing excessive arcing and pitting? Or could this contact failure just be the result of numerious on and off cycles?

One would think that with this being such a common problem that Winnebego would have come up with a recommendation to resolve this by now.