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Old 01-04-2014, 04:48 PM   #1
AimHigh's Avatar
Tiffin Owners Club
Join Date: Nov 2012
Posts: 93
Battery Boost

I know this has been beat to death but I have not been able to find my solution in the posts. I have a 05 Itasca Suncruiser 35A, gas model with an 8.1 L engine, with 2 house batteries and 1 chassis battery. I have been having problems with the chassis battery cranking the motorhome and when I use the battery boost switch it does not help. I eventually have to jump the chassis battery from the house batteries. In addition, whenever my chassis battery appears to be charged and I can crank the coach, and I put my slides in or out it drains the chassis battery and I can no longer crank the coach without jumpering the batteries. When I depress the battery boost, I do get a solenoid click but if there is additional voltage, it does not help. If I jump the coach and run it then I am able to crank it again with not problems unless I put a significant drain by using the slides or jacks. I'm sure I have a bad chassis battery but why won't my house batteries jump the chassis battery? How can I tell if my battery boost is working?

Any help is appreciated.

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Old 01-04-2014, 05:01 PM   #2
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Use a hydrometer to check each cell of your engine battery.

Then use volt meter on engine battery when boost button is pressed (need two people.) The voltage should increase confirming relay is working.

Finally, often when using boost you need to hold the spring loaded switch a few minutes to allow house batteries to bring up the engine battery.

It reads like your engine battery may need replaced.
George R. - Fulltiming since January '03
2007 Newmar Mountain Aire 3991
2012 Chevy Malibu LT1
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Old 01-04-2014, 05:06 PM   #3
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I think this link will shed some light. I have read your chassis battery has to have enough juice to kick the solenoid in for the boost to work. I had similar problem with my chassis batt not getting charged on shore power and was drained when radio was left on for a couple days. Had to install a Amp-L-start to charge chassis when on shore power. Good luck.
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Old 01-04-2014, 05:15 PM   #4
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could be as simple as cleaning the battery post/connections
1997 four winds windsport 38,000 miles
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Old 01-04-2014, 07:42 PM   #5
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My manual says to have the engine running when operating the slides,
2004 National Sea Breeze LX8375, Towing a 2012 Liberty.
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Old 01-04-2014, 07:55 PM   #6
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My slides wont move in or out with the engine running. 09 Safari Simba, Workhorse chassis.

I once had to hook up jumper cable to the coach batteries to start the gen.
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Old 01-14-2014, 08:13 PM   #7
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To all of you who replied to me, many thanks. Sorry it took so long to get back with the solution. The coach battery was in fact bad and once I replaced it all of the slides worked and I was able to crank it after operating the slides. I still can't figure why the coach battery has to have some juice in it for the battery boost to work, I men isn't that the whole purpose is to be able to jump your coach battery from the house batteries? Anyway it's happy trails again. Thanks and please keep up the great responses.

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Old 01-15-2014, 12:50 PM   #8
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Maybe your engine battery was so bad that the house battery was drawn when you used the boost switch. Just a thought but they operate in parrallel so the voltage would be even between them.
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Old 01-15-2014, 02:52 PM   #9
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Originally Posted by trampsrv View Post
could be as simple as cleaning the battery post/connections
Happened to me Sunday last.

And... That was exactly how I cured it.. (not the first time).

The first time I disconnected the house battery to run a proper load test.

Passed, flying colors

When I re-connected everything worked.. A great light dawned. I think this was the 3rd or 4th time.
Home is where I park it!
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Old 01-15-2014, 02:57 PM   #10
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I would double check if the boost switch is mow working. You could have two issues with one remaining.
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Old 01-15-2014, 05:11 PM   #11
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A bad battery can not be made better

If you had placed a digital volt meter on the battery when trying to use the relay boost you might have seen the voltage to low to operate. Point being, if you have a dead or shorted battery, applying the power from a good battery may not necessarily solve the low battery problem.

the shorted or low battery will suck down the power from the good battery thereby lowering the overall voltage low enough to not actuate the relay.
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Old 01-15-2014, 11:20 PM   #12
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You may still have a problem with your battery isolator / boost solenoid, when we bought our 04 Gulfstream I found the house batteries didn't get charged while driving and the boost switch did not work. Checked the solenoid in the pass side compartment with a volt meter and found that even when the solenoid was energized it did not connect the chassis & house batteries together for charge or boost. I disconnected the "Exciter" wire (little wires) on the solenoid and the solenoid clicked and engaged but no power through it so solenoid was faulty. Dealer replaced it and all is "Supposed" to be good now, time will tell. I did do some research on these solenoids and found 200 amp & 500 amp so I requested the 500 amp unit. When you think about it when you crank your engine especially a diesel it will draw over 500 amps and when you are using the boost button you want all the power you can get through said solenoid so the 500 amp unit is the only choice. I would recommend that you look for this solenoid on you coach and test it to make sure it works properly.

Good luck!
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Old 01-16-2014, 07:57 AM   #13
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As mentioned earlier the boost solenoid may not be working properly, or may be wired incorrectly. The easiest way to tell if it's working is start the engine. The chassis battery is always charged by the engine alternator. When the engine is started the solenoid is activated connecting the house batteries to the charging circuit.

If the solenoid is working properly both sets of batteries should be showing a charge on the One Place monitor. The chassis battery on our 2001 Adventurer would show a charge as high as 13.7 volts with the engine running. The house batteries usually showed 13.4 volts if they were being charged by the engine alternator. If the solenoid wasn't working the house batteries would show 12.8 volts while the chassis battery would show up to 13.7 volts.

Don't be fooled thinking that if you hear the solenoid engage it's charging the house batteries. In many cases a carbon film forms between the plunger and the internal contact. The film is from years of arcing between the plunger and the contact when the power is shut off. Over time the carbon film will get thick enough to insulate the terminals and not allow current to flow to the house batteries.

This same film won't allow the current to flow to the chassis battery when the Boost Switch is depressed manually. The solenoid will make a clunk like it's engaged but no current will flow.

Our solenoid failed in this manner, and when I went to get a new one the fellow behind the parts counter told me that was the way the majority of them fail.

If you determine you need a new solenoid. Be sure to get the proper one. It looks like the old Ford starter solenoid, but has a 100% duty cycle. They're readily available at almost any RV parts store, and cost about $30.00. Make sure it says it has a 100% duty cycle on the box. Remember it's engaged anytime the engine is running. A cheap one that isn't rated for this kind of on time will overheat and burn out in short order.

As a side note the solenoid in our Adventurer was located behind the top step of the main entry door. You had to remove a carpeted panel then a steel panel with a row of circuit breakers to get to it. If you do replace the solenoid be sure to disconnect ALL the batteries first. There's limited space in the area, and the last thing you want to do is remove a cable and have it arc against something. Replacement should take less than half an hour.
2013 Adventurer 32H
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