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Author Topic: Battery Boost/ Auxillary Start Solenoid Failures  (Read 1421 times)

Travlin Ken

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Battery Boost/ Auxillary Start Solenoid Failures
« on: October 12, 2015, 06:52:00 AM »
Over the years there has been much discussion of this topic. Failures seem to be common. I currently have my third failure. Some have disassembled, but no smoking gun for failure identified that I have found. I tore one down. Electrical contacts (copper) looked okay and coil resistance 7-8 ohms. Evidence of coil being hot- insulating tape charred.
Has anyone identified the real cause(s) of failure?
Some have gone to units with silver contacts. Others have gone to a marine solenoid (Blue Seas).
What is the long term life experience with these "improved" units?

Travlin Ken
2002 Itasca Horizon Diesel

Gary RV_Wizard

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Re: Battery Boost/ Auxillary Start Solenoid Failures
« Reply #1 on: October 12, 2015, 08:21:02 AM »
This complaint seems mostly to apply to the Trombetta brand solenoids used in Winnebago products. Apparently they are not of stellar quality.  I don't recall seeing a high rate of complaints on other brands, e.g. the common Intellitec Big Boy. You sometimes see complaints about a boost switch "not working" or batteries not cross-charging, but as often as not the problem is in the activating circuit rather than the solenoid itself.

It will be interesting to see the responses you get re replacement brands. Hopefully a consensus will emerge on the right choice.
Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL


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Re: Battery Boost/ Auxillary Start Solenoid Failures
« Reply #2 on: October 12, 2015, 08:32:51 AM »
I have a solenoid failure on a Winnebago Vista. Would not  be a problem except for the location, an arms length deep in an electric box behind a circuit breaker panel. You can just reach it with one hand.

Stupid engineering, to make a commonly replaced part so difficult to replace.


Just Lou

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Re: Battery Boost/ Auxillary Start Solenoid Failures
« Reply #3 on: October 12, 2015, 11:51:42 AM »
Travlin Ken,  your post describes the two failure modes rather succinctly.  While I do not claim to have done any in-depth research on the subjective of solenoid failures in RVs, I have made some interesting observations.

The majority of the Winni-Itasca Battery Boost/ Auxiliary Start Solenoid failures that I have seen, have been coil failures.  Winnebago doesn't (or didn't in the past) use much circuit logic in regulating the voltage they apply to the solenoid/relay coil.  The Trombetta coil used, is rated for continuous 12V operation.
  • For Boost/Aux Start functions the solenoid is fed voltage from the House batteries, which could be as high as 14.8 if the batteries are currently receiving bulk charge voltage.  This short duration procedure usually does no harm to the coil, but does present the highest current flow through the internal contacts of the solenoid.
  • For the charging of house batteries while driving, the solenoid simply receives voltage from the alternator, via an ignition controlled source, which can be near 14V continuous.  This longer duration procedure can cause coil failures due to heat.
Many other motor home manufacturers use a version of the BCCs designed by Intellitec or RV-Custom Products.  These BCCs generally add a bit of logic to the gating of voltage to the solenoid coil.
  • For Boost/Aux Start functions, battery voltage is applied to the solenoid in the simple manner as described earlier.
  • For the charging of alternate battery banks, from either engine alternator or House Converter, a voltage comparator is used to determine that a charging source is, indeed, present.  Timing and voltage thresholds are used to signal the circuitry to apply voltage to the solenoid coil when appropriate.  The point being, that this voltage is a somewhat regulated or derived voltage, and thus is closer to the coil specs than raw alternator or charger output.  Most of the Diesel versions of these BCCs use a pulsed voltage to keep the solenoid activated, just to avoid causing an overheating of the coil.
Possible solutions to repeated solenoid problems would depend on which failure type you are experiencing.
For coil heat (burn out) problems;
  • Selecting a solenoid with a 14V coil rating could be the answer.
  • Using a voltage divider on the coil input may prove effective.
For contact failures;
  • Selecting a higher contact current rated solenoid would probably be the best solution.
Most of us would hope to find a replacement solenoid with improved specs in both categories, but that can get expensive pretty quickly when you compare the prices of some of these solenoids.  I hesitate to make recommendations when it concerns spending other people's money. :)
'97 Bounder 34V (F53 w/tag), '99 Honda Accord EX