How To Extend The Life Of Your BDS and Boost Solenoids

[imnprsd]

I came across a video the talks about the reverse voltage affects on solenoids contacts and what causes "arcing" when you open the circuit that uses a coil... like solenoids and relays use.

And since a number of people are complaining about failing BDS and Boost solenoids, and I do not want to be next.

The video suggests you can extend the life of your solenoid/relay by just adding a reverse biased diode (like the 1N5400 silicon diode or Schottky SB560 diode) to the coil posts to absorb the reverse voltage (spike). Does it?

* If it's so easy to add a diode; and it only costs $1-$2 to do this, why haven't more owners been doing it? ...And which is better, a silicon diode or a Schottky diode?

* What is the downside? Is there any heat loss (Watts) when the BDS is on? ...What about the Boost Solenoid?

* And if it does make sense to add a diode does this upgrade only apply to the BDS latching solenoid since the coil is "always on" when you are operating the RV; and what about the Boost Solenoid that is a momentary switch and is only on when the button is pressed?

Note: The arcing occurs when you "open" the switch or turn off the BDS. This is caused by a collapsing magnetic field (coil). When you add the diode as shown current will pass through it to the battery because current always flows from a higher potential voltage to a lower voltage. In this case the coil could be 80V when collapsed and when the circuit includes a diode the current will flow to the battery and not to the solenoid points -- so no arc!

So is it a good idea to add a diode to our BDS and Boost Solenoid or not?

https://www.youtube.com/watch?v=0BPphesBGg0

Diode basics:

https://www.youtube.com/watch?v=bXEyCf1P0UU

[imnprsd]

WOOPS: I got out ahead of myself on this one.

CORRECTION: It would appear that adding a diode protects the Boost Switch on the dash (or Salesman Switch if we are talking about the BDS) from arching and not the contacts in the solenoid.

Here's the video that explains why adding a diode to your coil solenoid will help to extend the life of your switch that opens or breaks the circuit.

https://www.youtube.com/watch?v=bvDuyM2e4gw

And to answer my own question: The reason why haven't we heard more about this tip is because the BDS switch does not fail that often if at all, but this is not the case for the "Boost Switch" which can fail. So at this point I would say you could add a diode to the the Boost solenoid to protect the switch to the coil, but I would only do that if you find you are always using a "boost" to connect the engine battery to the house battery; and I don't know about you, but I almost never need to do this.

So never mind! ...And I hope you find the videos educational.

[US1]

I have the luxury of having an electronics geek at my job that I use for many of my electrical questions on electronics. Whenever he designs me a system that has relays in it, he will install one for the same reason you stated if the relay does not have one built in

[Morich]

The idea is pretty simple and why it is not done is also a pretty simple thing.
It is not done as the need or benefits does not work out to be enough to merit the extra.

What U-tube has opened up is an area where anybody that has an idea can set it out and use it to sell adverts. One way to sell more adverts is to be way out front on things to make it sound really exciting. Whether it is a new idea is often not even mentioned and the guy posting the videos is not concerned with whether it really is a good idea, just whether it generates lots of traffic!

The way to cut down arcing was dealt with way back before ignition points on cars and even those are now obsolete.

When electronics are really high dollar enough to merit the extra expense the methods to prevent arcing are pretty common -just not used on cheap stuff like our solenoids.

But reinventing the wheel is still a good field to be in!

[imnprsd]

Thank you "US1."

"Morich" is also right, because it takes 10 years for the wear to occur.

Oh wait... many of us RVers are faced with replacing the Boost solenoid, which is a momentary switch, and prone to heavy arching depending on how you hold down one switch and release the other. I.e., if you are trying to crank you generator or engine while holding down the boost switch, then you have a lot (repeat a lot) of current going through the solenoid, and that has to create some additional wear on the contacts if you "break" or "open" the circuit by releasing the "Boost Switch" before you let go of the generator start or engine start button.

So I can see the value of using a diode on the Boost Solenoid to extend it's life, but not the BDS since it's a latched solenoid vs. the Boost Solenoid which is a momentary switch.

The point being: Who cares what happens 10 years from today?

Answer: Some of us do and some of us don't!

[imnprsd]

To clarify:

* Adding a diode as discussed protects the low current coil switch and not the high current contacts inside the solenoid/relay.

* To ensure your BDS and Boost Solenoid last the longest possible, you should buy the solenoid that uses silver contacts vs. copper.

* And when it comes to using you boost switch, you should make sure you release your ignition-key when starting your engine, or you need to release the generator start switch... before you release the momentary "boost switch."

[Phil G.]

Well, at least in my Class C motorhome ... the solenoid being called the "boost solenoid" in this discussion is the solenoid used to connect the engine's starting battery to the coach's 12V battery bank for both boosting of the chassis 12V system for engine starts - and charging of the coach batteries via the alternator whenever the engine is running.

In other words, in my motorhome all 3 batteries (two deep cycle 12V in coach and one 12V under the hood) are connected together in parallel with each other and held together by this same solenoid that can also be activated via the momentary boost switch on the cab dash.

What this means is - this solenoid gets engaged and dis-engaged at least every time the engine is started or turned off ... hence many cycles over the RV's lifetime. I'm own my 3rd boost/charging solenoid in 14 years. The first solenoid was the stock one that Winnebago installed and it only lasted for 3-4 years. The second and third solenoids were/are heavy duty 12V continuous duty ones with silver plated contacts ... I'm still on the second one of these heavy duty solenoids and I don't know why the first one of these heavy duty solenoids didn't last "forever"!?

[imnprsd]

Signals crossed?

The "Boost" solenoid I'm referring to is the one controlled by the switch usually mounted on the dash by the driver. It connects the engine-chassis batteries to the house batteries.

The boost solenoid is not always connected. It is a momentary switch.

There is a starter solenoid that is used to start your engine and is only connected to your engine-chassis batteries.

* As noted, you want to buy the solenoid that uses silver contacts inside to ensure you get the longest solenoid life.

* I use my Boost switch maybe once every 2 years, but I can tell you it takes a beating and people have reported their dash switch has failed on them in the past. This is due to the arching at the dash switch and you can avoid this by connecting a diode as described above.

==> So if one day you push your boost switch and nothing happens... now you know it could be the dash switch. so just pope it out of the dash and short the 2 wires to see if it that is the problem.

[Phil G.]

Originally Posted by imnprsd

Signals crossed?

The "Boost" solenoid I'm referring to is the one controlled by the switch usually mounted on the dash by the driver. It connects the engine-chassis batteries to the house batteries.

The boost solenoid is not always connected. It is a momentary switch.

There is a starter solenoid that is used to start your engine and is only connected to your engine-chassis batteries.

* As noted, you want to buy the solenoid that uses silver contacts inside to ensure you get the longest solenoid life.

* I use my Boost switch maybe once every 2 years, but I can tell you it takes a beating and people have reported their dash switch has failed on them in the past. This is due to the arching at the dash switch and you can avoid this by connecting a diode as described above.

==> So if one day you push your boost switch and nothing happens... now you know it could be the dash switch. so just pope it out of the dash and short the 2 wires to see if it that is the problem.

As I stated in my post a bit earlier, the same solenoid in my motorhome is used for two things: It connects all batteries together in parallel with each other (coach batteries and chassis battery) when activated by the momentary boost switch on the dash to start the engine when the chassis battery is weak ... AND ... it gets activated and held activated automatically when I start the engine so that the alternator charges all batteries together by activating that same solenoid to connect them up all in parallel with each other.

So, this solenoid gets used "at lot", well beyond only for rarely boosting to start the engine when the chassis battery is weak.

I am thinking that all this use is hard on the solenoid contacts , even with silver coated ones. Corrosion and/or pitting of the contact surfaces proabably takes it's toll over time. As I said, I'm on my second silver contact plated heavy duty replacement solenoid in 14 years of RV'ing. The original solenoid as installed by Winnebago did not last long at all.

[Bobn1957]

All DC circuits benefit from a blocking diode across a relay coil. When the electrical field in the coil collapses it creates a large surge of electricity in reverse of the previously applied voltage (just like a car spark coil). The issue of contacts burning because they are interupting a large current a condenser across the contacts would help (just like old school automotive ignitions).

[imnprsd]

Bobn1957: I do remember adjusting the dwell of my Ford Mustang ignition points and replacing the capacitor.

So are you saying the use of adding a condensor (aka capacitor) to absorb the back EMF; or adding a reverse biased diode to block the reverse current spike (arch) is better for extending the life of our BDS and Boost Solenoid?

If so, I wonder what percentage of these solenoid switches are failing, because no one is adding a $1 diode or capacitor to either block or absorb back EMF voltages and/or spikes?

Is there any downside in terms of current drain? And if so, is that why you recommend the use of a capacitor over a diode?

[Bobn1957]

I would recommend using both the capacitor and the diode, the diodes go across the coils of the relays and the capacitors go across the points. Not being an engineer I'm not sure how large the capacitors need to be, as for the diodes 1 amp should be sufficient. If I was going to prioritize I would go with the diodes first. The only downside I see is if the capacitor shorts the circuit stays on. This is for DC circuits only.

[NormD]

There seems to be confusion here, perhaps my own. The boost relay is continuously ON when the engine is running, which charges the house battery, and momentarily ON while the momentary switch on the dash is pressed. The contacts on the boost relay never see more than a few volts across them (like the difference, between a 13 volt battery and an 11 volt battery = 2 volts), but may see very high current. The burning of the contacts due to high current leads to eventual failure of the relay
.
When the relay coil is energised a magnetic field builds up around the coil. When the coil is deenergised, the magnetic field around the coil collapses, which generates a voltage of opposite polarity to that which energised the coil. The voltage increases until either the stored energy is dissipated by arcing (think of an electric fence) or the field collapses before arcing or insulation damage occurs. A diode placed across the coil can prevent this voltage buildup. A Schottky diode offers a slightly lower voltage limit than a standard silicon diode, and is therefore a waste of money for this application. The diode offers some protection against breakdown for the coil’s wire insulation, but the energy dissipation will most likely occur at switch contacts. So, a diode across the coil would not be expected to add anything to the life expectancy of the boost relay coil.

If you are experiencing failure of the coil, it is most likely due to the high temperature resulting from operating the relay for long periods of time. This can result in failure of insulation or internal connections. In my RV the manufacturer buried the boost relay in insulating foam, so only the thin mounting bracket and copper wires carried away the heat.

[Bobn1957]

It would be interesting to see the waveform across the contacts and the coil of the Boost Relay on an Oscilloscope with and without the diode/capacitor. Just how high is the voltage spike? How long does the current keep the arc alive?

[imnprsd]

NormD: I don't know what type of RV you have, but my 2004 Itasca Horizon 40AD has 2 solenoids and the Boost Solenoid is NOT "Hot" or "on" all the time. (See schematic below.)

* My boost solenoid is a controlled by a momentary solenoid/switch and has nothing to do with the ignition key on or off; and this boost solenoid has nothing to do with my alternator charging my batteries.

==> When I press the Boost Switch on my dash the house battery is "momentarily" connected to my chassis-engine battery and this creates a "boost" to jump start either my engine or generator. That's all.

==> In my RV, there is a separate Battery Isolator circuit that enables my alternator to charge my engine and house batteries, but this circuit does NOT energize the Boost coils. So the boost solenoid is normally "off."

That said, I have to disagree with your premise regarding the function of my boost solenoid (being "on" all the time), but maybe your coach is different. What do you drive?

* The BDS or "Salesman Switch" is a latching solenoid (constant duty) and this one is "on" all the time. So if you use a diode here you will be loosing 0.7V across the diode all the time, which I'm not sure that matters so much? ...But I will add, I have never heard of the salesman switch... the one at the entry door in my RV going bad.

So I don't see the point of adding a diode to the BDS, but the contacts coil in the BSD are prone to shorts... probably caused by wear-and-tear from switching it on-and-off.

So maybe attaching a condenser to the positive terminal of the solenoid would be a good idea? ...And just to be clear, you do connect the condenser on the positive or negative side of the solenoid coil, right?

Plus, capacitors do not generate heat like diodes do. ...But capacitors can short to ground if too much voltage pass through them. So this would become a potential maintenance item after about 5-10 years of use, I would think? ...Ergo, there are perhaps good reasons coach manufactures elected to leave these things out.

POINT: This thread maybe "overkill" but for those of us who like to know how these systems work, it's all in a days pay.

I also do not know how big a capacitor needs to be, but since you hook this up in parallel to ground, as in the outer case is the ground, then I'm sure a cheap $4-$7 ignition condenser will suffice, since these things are designed to handle very large back EMF in 12V ignition applications where the voltages are as high as 25,000V.

The picture below is a common ignition condenser and you can buy these everywhere. Of course, I would buy the name brand if I were you, but maybe the cheap ones are just as good and reliable?


To recap what I think "Bobn1957" is saying:

* Adding a capacitor will protect your solenoid points inside... just like the condenser was used to keep a pre-80's ignition coil with point-contacts from burning out.

* Adding a reverse bias diode as shown in the picture above will help to prevent your dash switch from failing prematurely.

[Bobn1957]

A reversing diode only flows electricity that is created when the field collapses so no .7 volt loss.

[Bobn1957]

Another thing as mentioned in the video the reversing diode will help protect the 12-volt electronics like the household surge protector.

[cbeierl]

Originally Posted by imnprsd

NormD: I don't know what type of RV you have, but my 2004 Itasca Horizon 40AD has 2 solenoids and the Boost Solenoid is NOT "Hot" or "on" all the time. (See schematic below.)

* My boost solenoid is a controlled by a momentary solenoid/switch and has nothing to do with the ignition key on or off; and this boost solenoid has nothing to do with my alternator charging my batteries.

==> When I press the Boost Switch on my dash the house battery is "momentarily" connected to my chassis-engine battery and this creates a "boost" to jump start either my engine or generator. That's all.

==> In my RV, there is a separate Battery Isolator circuit that enables my alternator to charge my engine and house batteries, but this circuit does NOT energize the Boost coils. So the boost solenoid is normally "off."

That said, I have to disagree with your premise regarding the function of my boost solenoid (being "on" all the time), but maybe your coach is different. What do you drive?....

As you can see by inspecting the Automotive Wiring Diagram and the Chassis Wiring Installation diagram for your 2004 Horizon the battery boost switch on the dash has three wires connected to it (LR, LS, and either LLJ or JJX, depending on whether or not you have an MMDC). LR is the activation line going to the battery boost solenoid, LS is an always-on power source, and LLJ (or JJX) are run-only power sources.

In its normal position the battery boost switch connects LLJ (or JJX) to LR, thus connecting the battery banks whenever the engine is running. Depressing the switch to its momentary position connects LS to LR, thus immediately activating the solenoid and connecting the battery banks together as long as the switch is held down.

[cbeierl]

Here's an long, old thread that you may find worth reading: Yet another solenoid bites the dust!

It appears that a factor in the failure of many of the battery boost solenoids is the fact that these are 12V solenoids but they are getting an activation voltage of around 14.5V from the engine alternator. As discussed in the above thread, adding some resistors or diodes in series with the activation wire can reduce that voltage enough to lead to much longer solenoid life. After two solenoid failures within the first 3 years of service on our coach I replaced the solenoid with the silver contact version and added a couple of resistors in the activation line (detailed, with pictures, in the above thread)--it's been 13 years since I made that change and that 3rd solenoid is still going strong!

[Bobn1957]

I agree that using a premium relay will help with the longevity of the relay, but suggest that a 12 volt relay would be engineered for the actual 13.2 volts of a fully charged 12 volt battery.