Community Forums

Takawira · 01-24-2017, 07:46 PM

I'm new to the rv life. Recently bought a used 1991 Mallard Sprinter. It has a Ford 460 automatic in it. Previous owners had no manuals at all. So I'm learning as I go. However I still can't figure out how to jump start this thing. It has 3 batteries and they are all linked together, meaning the chassis and coach batteries are all combined. Clearly I'm running into battery drain problems and would really just like to have some way to jump start whenever I need to. Right now I don't see an obvious power source that I can tap into (I have an external battery for jumping my other vehicle). Is there something magical about how the engine gets power? Thanks a bunch 😊

BFlinn181 · 01-24-2017, 08:30 PM

Your RV should have 2 separate battery systems. The chassis battery is for starting and driving functions. The house batteries should be for running interior lights, water heater, refrigerator, water pump, furnace, etc.

The battery groups are electrically isolated from each other until a charging current is detected (over 13.4 v) then the batteries link to the charging current. When the shore cord, engine, or generator is off, the batteries are again independent. Often a 'boost' switch on the dashboard can be held down to temporarily join the batteries together to 'jump' the chassis battery to start the engine if the battery is weak.

This is all done with electric solenoids (relays) that can fail. Often they fail so no connection is made, or sometimes they fail by staying connected full time, creating the problem you describe.

Google images will show you battery isolation solenoids and battery disconnect solenoids. Your RV might have them in a protected location. Often under the hood in a plastic box will be the solenoids that should control the batteries.

Often RVs will have a battery disconnect switch inside the entrance. This allows you to disconnect the house batteries (and often a separate switch for the chassis battery) for storage. This reduces the chance that the batteries will be discharged when the RV is not in use.

This link may be of use to you.

Good luck with your new rig.

Takawira · 01-24-2017, 08:59 PM

Thanks! I'll look up some solenoids for the future but don't know if it will be of use right now. My best guess its that the previous owners probably created some kind of bypass because my battery disconnect doesn't work. So I'll have to figure it out. But I don't think that I can isolate my chassis from coach batteries. The way they are connected is the problem. Like I said I have 3 batteries, all cables connect to the one in the center and the other 2 batteries supply juice to this middle battery. So basically I'm thinking solenoids might still not solve this quandary until I can trace all the wiring.

Takawira · 01-24-2017, 09:00 PM

I don't think you provided a link though.

BFlinn181 · 01-24-2017, 09:10 PM

If you click on the two underlined words, you'll find a link to "12 volt side of life" that explains RV electricity. Here's the link again.

Here it is 'bare' The 12volt Side of Life (Part 1)

Gary RVRoamer · 01-25-2017, 10:59 AM

Only one of those three batteries are direct-wired to the starter and you can jump-start that just like you would on a car, using another vehicle or external battery.

You may be able to use the other two (house) batteries as the source as well, as was explained above. You could also use jumper cables to them, but the method varies a bit depending on whether the other two are a 6v pair (in series) or two 12'v in parallel. If 12v, just jumper to the positive and negative terminals like usual, but if they are a 6v series pair, you need to jump to the positive on one and negative on the other to get 12v.

wa8yxm · 01-25-2017, 11:33 AM

Though as someone said your RV **SHOULD** have two INDEPENDENT (when sitting) battery systems.... Well some folks will combine for assorted reasons such as: Some RV's do not charge chassis battery when plugged in. Combining into one bank fixes this.
Some the isolator fails and they do not charge the house when driving Again. fixes this.
Some want the added "House" capacity.

In any cases, if you need to jump start.. You really have only one battery, Or it may have 2 or 3 or half a dozen or more Sections but it's all one "Battery" (collection of cells) so you jump start normally

Hook to the Positive on both vehicles
Hook to the Negative on the Rescue vehicle
Hook to the CHASSIS or ENGINE part on the RV (last connection is made remote from the battery to avoid an explosion)

Run rescue engine for a few minutes, then hit the starter.

When disconnecting, "Break" the "Remote" connection first

Why the Remote: Batteries give off Brown's gas. 2 parts Hydrogen, one Oxygen.. that is the ideal proportion to go BOOM if some idiot adds a spark,, and with that much battery it can be a nice BIG boom.

4x4van · 01-25-2017, 12:35 PM

Is your coach a Class A, or a Class C? You say that all 3 batteries are wired together. Where are they located? Is it possible that the previous owner installed 3 house batteries, and your chassis battery is a 4th, located elsewhere?

If a Class C, the chassis battery should be under the hood; right (passenger) side. If equipped with a single house battery, that is also under the hood, left (driver) side. Since 3 batteries certainly won't fit under the hood, they would have to be located elsewhere.

If you have a Class A, then the above doesn't apply, but there could STILL be 3 house batteries and a 4th for chassis located elsewhere. Unusual, yes, but so is wiring chassis & house batteries together.

Or, as already said, the previous owner bypassed the isolation solenoid (which is usually used in most if not all RVs of that vintage) and wired all of them together. If that's the case, you MUST restore the isolation function. That will allow all batteries to charge while driving (most RV's of that vintage will not charge the chassis battery from shore or genny power, only alternator), but prevent the chassis battery from going dead while camping.