Jump starting chassis batteries

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Jump starting chassis batteries

December 19, 2021, 03:01:35 pm

Rather than piggy-back on an earlier post, I'll start a new one with tag that may help future searches.

I've got a 2003 U320 4020 with the chassis batteries mounted behind the engine. If I'm going to attempt to jump start the engine where on the motorhome do I connect the jumper cables (yes--I know, not the $10 model) lol. Also, my temps are in the mid-40's, so I'll be running the generator to heat the engine prior to jumping. My boost switch does not seem to be working.

I actually have a perfect storm of several needs to address, but getting the bus cranked is my most immediate need.

Thanks!

Steve Rushing

Re: Jump starting chassis batteries

Reply #1 – December 19, 2021, 03:35:13 pm

I would put the cables on the chassis batteries.

Re: Jump starting chassis batteries

Reply #2 – December 19, 2021, 03:42:03 pm

Steve, on my 2001 U320, there are battery connections with red and black covers located facing rearward near the air dryer. Remove covers and connect jumper cables there.

Re: Jump starting chassis batteries

Reply #3 – December 19, 2021, 04:28:54 pm

I had to do that after we bought the coach as the PO had installed a new isolator but mixed up the cables and all batteries were flat. Our U300 has the engine/chassis batteries just in front of the rear bumper. I just hooked up the jumper to them, fast idled the toad for 10 minutes and it started right up.

I bought a HD set of cables and keep them under the seat in the toad. I've jumped a lot of people. Good karma.

Pierce

Re: Jump starting chassis batteries

Reply #4 – December 19, 2021, 05:01:38 pm

Thanks for the quick responses!

Rudy--I can't find the posts in the area you describe. They may be in plain sight, and I'm simply not recognizing them.

I'm going to try by connecting to the batteries--can just get underneath. I should be able to connect to the first battery I see (red/red, black/black)--correct?

Thanks!
Steve

Re: Jump starting chassis batteries

Reply #5 – December 19, 2021, 06:10:24 pm

Steve, sent you a PM

Re: Jump starting chassis batteries

Reply #6 – December 19, 2021, 06:42:21 pm

If a boost switch does not close the boost solenoid, just put your jumper cables on both sides of the boost solenoid to simulate the solenoid closing.

Or you could put 12v on small boost solenoid pos terminal to see if solenoid will close.

You could put jumper positive on boost solenoid side that is connected to start bank. Use any frame part for jump negative.

Re: Jump starting chassis batteries

Reply #7 – December 19, 2021, 07:58:33 pm

You can use the aqua hot to heat the engine.

Re: Jump starting chassis batteries

Reply #8 – December 19, 2021, 08:08:15 pm

Quote from: Barry & Cindy – December 19, 2021, 06:42:21 pm

If a boost switch does not close the boost solenoid, just put your jumper cables on both sides of the boost solenoid to simulate the solenoid closing.

Or you could put 12v on small boost solenoid pos terminal to see if solenoid will close.

You could put jumper positive on boost solenoid side that is connected to start bank. Use any frame part for jump negative.

While this will certainly work electrically, working with jumper cables in that tight an environment with so many ground sources (any metal) around with the extremely high amps available is NOT how I would do it. Instead, remove the wire from one large lug and ADD it to the other large lug. You have not electrically done the same thing-- created one large battery bank from the two separate ones. They will now charge and discharge together. So, one has to be more electrically savvy!

Agree, to prove the solenoid I have no problem disconnecting the small "signal"/positive wire and using any small gauge wire to go from the large "always hot" lug to the positive signal terminal. If the solenoid "clicks" and joins the two large lugs, you know the signal from the dash is not reaching the boost solenoid. If not click, the solenoid is bad.

Re: Jump starting chassis batteries

Reply #9 – December 19, 2021, 11:57:45 pm

Thanks for all of the suggestions! Honestly a lot of the info is currently (no pun intended) above me. Give me an old Ford 300/6 or Chevy 327 and I'm good to go...but this is my first diesel, and I'm still learning some of these parts along with their locations.

I did put a 15-amp charger on the first battery (did not remove the connections) and after about three hours it showed 100% charged. When I tried starting the engine did turn over slowly, but only for about five seconds. Then only blinking dash lights. (BTW--the engine had heated to 102 and the oil was at 60.)

I think my alternator may be bad, which is why the batteries are down. Two weeks ago I took the rig on a 100-mile run to make sure everything was good to go for a planned trip last weekend. Dusk set-in about 1/2-way into the trip, so the headlights were on...along with the radio and everything else on the dash. At the end of the drive I topped-off the fuel tank with the engine off, and parked in the back part of my driveway--about 85-feet from my 50-amp plug-in. Two days later, when I tried cranking it, the engine dragged, and then the dash lights blinked with the familiar buzzing sound you get when a battery fails.

Yes, the check engine has come on recently during a short 50-mile drive, but it wasn't on during the above 100-mile drive.

As I said perfect storm. I learned my boost doesn't appear to work, and also my aux air compressor isn't working. In both cases neither button lights. The compressor is another new gadget for me, but I know it was working back in the spring while I was at MOT having the rest of the rig serviced, and they replaced the 6-pack and some other items related to the air system replaced because the air compressor wasn't shutting off as it should have.

I'm going to put the charger on again tomorrow morning before I head to work. What I'd like to try tomorrow evening is a combination of the again-charged batteries, and jumper cables connected to my Ram 4x4.

Quick questions--
1) Is it possible I only charged the one battery to which the charger was connected?
2)Where is the boost solenoid?

I'll get to the alternator and aux air, after I get the bus cranked and moved back to my 50-amp pole.

Thanks!
Steve

Re: Jump starting chassis batteries

Reply #10 – December 20, 2021, 12:16:51 am

When batteries show 100% but don't seem to put out the amps, it's time for a load test. If you separate the batteries, you can charge and load test to see if they or one is bad. Load testers are cheap. If the battery(s) are low, the alternator should put out in the 14 volt range. Flat batteries or frequently deep discharged batteries may not come back.

Another reason for two voltmeters on the dash and in your line of sight. Good to be proactive instead of on the defense when problems first start.

Ford 300/6 is a great engine. Used a lot in gas or propane generators where they can rack up thousands of hours without a problem.

Pierce

Re: Jump starting chassis batteries

Reply #11 – December 20, 2021, 08:19:32 am

Pierce is correct. Fully charge the batteries and have them LOAD TESTED. Any place that sells batteries can do this in a matter of a few minutes.

While driving, what did the voltmeter on the dash show?

If you connected the charger to the positive and negative terminals of one of the 12 VDC batteries, then yes, both/all batteries in that bank would be charged, since they are wired IN PARALLEL. Yes, this assumes the battery connections are clean and tight.

Re: Jump starting chassis batteries

Reply #12 – December 20, 2021, 09:21:05 am

Quote from: wolfe10 – December 20, 2021, 08:19:32 am

Pierce is correct. Fully charge the batteries and have them LOAD TESTED. Any place that sells batteries can do this in a matter of a few minutes.
While driving, what did the voltmeter on the dash show?
If you connected the charger to the positive and negative terminals of one of the 12 VDC batteries, then yes, both/all batteries in that bank would be charged, since they are wired IN PARALLEL. Yes, this assumes the battery connections are clean and tight.

Excellent point about the battery connections clean and tight. More than once, I have cranked the engine and then after starting, I've gone back to put my hand on the terminals. Several times, they have been warm, a couple of times too hot to touch. Good to take a second and pull then clean at least once a year. I like the green and red felt rings.

Pierce

Re: Jump starting chassis batteries

Reply #13 – December 20, 2021, 10:48:25 am

Quote from: SRushing – December 19, 2021, 11:57:45 pm

I think my alternator may be bad, which is why the batteries are down.

When the battery doesn't get charged in a car or PU truck, the alternator always gets the blame (or in really old vehicles, sometimes the external voltage regulator).

It's a bit more complicated in a RV with two separate battery banks.

Your problem might be the alternator itself. It could also be the alternator wiring (Excite wire broken/improperly connected).

Or your problem could be the battery isolator. It might be improperly connected, or it might have some kind of internal failure.

OR, as stated above, bad battery/charging cables or broken/dirty connections between cables and devices.

Check the other stuff first, before you run out and buy a new alternator.

Re: Jump starting chassis batteries

Reply #14 – December 20, 2021, 11:18:04 am

Yes, if you THINK the alternator may be bad, it is very easy to diagnose that vs battery isolator.

All you need is a digital voltmeter.

Let us know and we can provide the easy steps to diagnose.

Re: Jump starting chassis batteries

Reply #15 – December 20, 2021, 11:21:28 am

Just a note.. The boost "jumper studs" may have 2 rubber covers over them.. may not have them, I don't.

Re: Jump starting chassis batteries

Reply #16 – December 20, 2021, 05:33:55 pm

Quote from: SRushing – December 19, 2021, 11:57:45 pm

I did put a 15-amp charger on the first battery (did not remove the connections) and after about three hours it showed 100% charged. When I tried starting the engine did turn over slowly, but only for about five seconds. Then only blinking dash lights. (BTW--the engine had heated to 102 and the oil was at 60.)

Thanks!
Steve

If your chassis batteries were flat, and they showed 100% state of charge after only 3 hours at 15 amps, your batteries are toast.

Re: Jump starting chassis batteries

Reply #17 – December 20, 2021, 06:12:22 pm

On my 03 there is a + and - post inside the side door that you would open to see the batteries and air conditioning condenser ( behind the drive wheel on the drivers side) . It is near the outside skin. There is also a + and- post on the right side of the motor if you open the engine rear door. Both can be accessed from the outside of the coach.

Keith

Re: Jump starting chassis batteries

Reply #18 – December 20, 2021, 09:22:19 pm

Thanks, all. Great info, and insights. I'm sure at some point there will some other newbies who can use all/some of this to their advantage. For those of us not versed in what, and where many of these parts are it can be a bit intimidating to reach out to those who speak motorhome. I've done enough shade tree on my old cars and trucks to know sometimes you just have to stop and ask.

It was cold and rainy here today, so I'm not crawling back under there until Wednesday.

In the meantime, there are a couple of points to highlight:

1) The lowest the voltmeter showed at any time was approximately 11.5. After charging it was showing just past 13.
2) My comment about the alternator was borne of not knowing more about battery isolators. I still don't know where this is located.
3) I haven't checked connections, yet. It seemed charging first might be the easier, "I hope this works" solution.

After more checking underneath on Wednesday I'll have more info on the state of the connections.

Thank you, everyone, so much!

Steve

Re: Jump starting chassis batteries

Reply #19 – December 20, 2021, 09:39:26 pm

Quote from: SRushing – December 20, 2021, 09:22:19 pm

battery isolators. I still don't know where this is located!

Steve

On the forward wall of the engine under the bed. If you follow the big cable on the alternator forward you will find it. Splits and goes to the different batteries
Scott

Re: Jump starting chassis batteries

Reply #20 – December 20, 2021, 09:49:29 pm

Quote from: SRushing – December 20, 2021, 09:22:19 pm

2)Where is the boost solenoid?
...battery isolators. I still don't know where this is located.

Like Scott says, lift up the mattress platform and look down in the engine bay.

Should be a blue aluminum box with cooling fins. 3 posts. Center post is alternator input. Outer posts connect (probably indirectly - through the BOOST solenoid) to battery banks.

Link below to a post with photo. Ignore the Trik-L-Start (small blue, yellow and black wires). It is not standard factory equipment (but it is a good add-on device).

TRICK-L-START Install How easy is it?

Look on your B-2126 Automotive Wiring Diagram (in Owner's Manual). See .pdf file below for typical example. The area outlined in red is the "Aux Start/Isolator Panel" located under the bed platform. The isolator is the rectangle on the right side of the red box. The BOOST solenoid is right next to it. Aux Start Relay is in upper left corner. Everything in the red box should be located on or near the panel in your engine bay.

See if you can locate these items on your coach.

Re: Jump starting chassis batteries

Reply #21 – December 20, 2021, 10:31:26 pm

Found on forum a new example

Re: Jump starting chassis batteries

Reply #22 – December 21, 2021, 08:34:09 am

Quote from: Chuck & Jeannie – December 20, 2021, 09:49:29 pm

Link below to a post with photo. Ignore the Trik-L-Start (small blue, yellow and black wires). It is not standard factory equipment.

Trik-L-Start is not factory equipment but if you don't have one or something similar you should get one to keep your chassis batteries charged.

Keith

Re: Jump starting chassis batteries

Reply #23 – December 21, 2021, 09:22:06 am

As you have likely learned, allowing a battery bank to get down to 11.5 VDC materially shortens battery life AND can give you a lot of "Computer errors" in engine and transmission.

So, until voltage is at least 12.2 VDC, do not waste time trying to troubleshooting electrical issues.

Re: Jump starting chassis batteries

Reply #24 – December 31, 2021, 06:55:19 pm

Ok...between a heavy work schedule and rain I finally had time to get back to my coach today. Thanks to Rudy for the phone calls and help in locating jump-start lugs that most probably don't exist.

I still can't get it to start. Even tried jumping with a connection to the first battery from my Ram 4x4.
Additional notes...
A) I've checked every connection I can reach--none are loose. I can't reach the back to batteries, and I haven't chased to the starter to check its connections.

B) With not much to lose at this point, I used jumper cables (red/red) to connect/bypass the boost solenoid. Still didn't crank.

C) After charging the batteries the dash voltage guage shows between 12 and 13. After bypassing the solenoid it showed 13.
Turning the key didn't seem to draw much if any.

When I turn the key all I get is intermittent flashing on the dash with a slight clicking sound. When this first began the engine did just barely turn--probably not a full revolution.

Please remember, the rig is about as low it as it can get--almost on the rear tires. My aux air isn't working either. I mention this before extreme crawling in the already tight areas is suggested. I can get under it (I own a business that requires some of us to spend time in tight crawlspaces,) but some spots may be out of reach.

I'm adding pictures to show what I'm seeing from the bedroom hatch.

Suggestions/help?

Thanks!
Steve

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