Keep Boost/Aux Function with DC-DC Charger

DustyDude · 06-05-2023, 12:41 PM

I have upgraded my coach batteries to 400A of lithium which I assume may be too much for my 210A alternator to handle on a long-term basis. I had planned to install a 30A DC-DC charger between the mode solenoid and the coach batteries so I could keep the option to use the Boost/Aux function in case I ever need to jump a dead chassis battery. However, the existing cable is too large for the charger (6AWG max) which makes me think this may be a bad idea.

I am now thinking about installing the DC-DC charger directly between the chassis battery and coach batteries. Then install a 100A circuit breaker between the mode solenoid and the battery bank which can be left off (open) to avoid over-working the alternator, but I can close the circuit any time I need to use the boost function.

Do you think this would work? Have you accomplished this goal in a different way that may be better?

l1v3fr33ord1 · 06-06-2023, 04:30 AM

Craig-

A simple solution would be to remove the "KE" wire from the battery boost switch. "KE" is the wire that sends 12V to the switch when the ignition is on.

JLUSoCal · 06-06-2023, 07:08 AM

That's an interesting solution to remove the KE wire. I have Lithium and solar and I don't care to have it charge sometimes as I know at my destination I might not need. For instance, if I'm just heading back home, the solar will recharge in a day, and I don't need a battery once home.

Perhaps you can put a switch in the cab to control that line? A simple solution for the option. And it leaves the ability to run the engine when camped on cloudy days. I've done that a time or two as the generator is much more noisy OR I want both of the engines and their related chargers running to keep the runtime down.

DustyDude · 06-06-2023, 07:17 AM

Thanks for your reply. I assume removing this wire would also disable the Boost function as well. Or, are you saying that this wire would only impact the charging while the engine is running?

l1v3fr33ord1 · 06-06-2023, 07:57 AM

Quote:

Originally Posted by DustyDude

Or, are you saying that this wire would only impact the charging while the engine is running?

The way I read the diagram (links here and here), and from what I learned about other Winnebago models with a similar circuit design, removing the "KE" wire should defeat the ignition-switched cross-charging but still allow the battery boost function. The "secret decoder ring" that lists circuit designators is here.

What's left when you remove the "KE" circuit from the switch is an "LS" and an "LR" wire. The "LS" is a feed from the house battery bank to the switch. The "LR" is the feed from the switch to the battery boost solenoid.

You should be able to test this fairly easily. Note: I've always been a bit hazy on the battery boost switch. It seems to me there should be three positions:

1) Center- Off
2) Up (or Down)- Connect "KE" to "LR"; should snap and stay in this position
3) Down (or Up)- Connect "LS" to "LR"; should be press and hold, with spring return to center position (also known as a "momentary" switch action). This is what you would perform manually to connect the house and chassis battery banks for "boost."

Your tests will bear me out or determine if my ideas are poor ones.

DustyDude · 06-06-2023, 08:04 AM

Mark,

Your approach sounds much better than what I had planned. I have been reviewing the documents you linked, but kept getting lost. I should have some time in the next couple of days to experiment and will let you know.

Thanks for sharing you idea.

**creativepart** · 06-06-2023, 08:28 AM

You are right to worry about the alternator charging 400ah of Lithium. As you said, if you leave a place with low batteries those LFPs will pull massive amounts of power.

I have basically the same kind of setup on my Adventurer. I removed the solenoid completely.

I installed the DC2DC charger between the chassis battery and the house bank. I used a Victron model so I didn’t need an ignition trigger, other brands don’t have that auto on/off feature. But there is a trigger wire on the solenoid if you need to use one. I just didn’t want to bother figuring it out and I have other Victron gear so it was a best case for me.

I lost the dash Aux function when I disconnected the solenoid. I figure I’ve only used that feature once in 6-years and I could always use jumper cables from my toad if I every needed it again.

I also lost chassis battery charging when on shore power. There were easy ways to deal with that but it must be considered. Leaving the chassis battery “on” while on shore power you will run that battery dead in a few days. In fact, after disconnecting the BIM to install everything in my driveway, I was plugged into 30amp and within 5-days the chassis battery was dead. It was an old original battery but it sure pointed out the issue.

I solved it with an Amp-L-Start device that works great but may be tough to get right now.

So when that battery died I got to tryout my jump start plan right away and it worked just fine. So I feel I’m OK without the dash aux start switch. You may feel differently.

DustyDude · 06-06-2023, 09:27 AM

In a previous Class C I replaced the solenoid with a BIM which solved the alternator issue, but I lost the Boost function which didn't bother me at the time. However, when I traded it in on my current Class A the dealership was a little concerned that it no longer had that function. I am going to experiment with Mark's idea to see if I can have my cake and eat it too.

All of the components I have installed are Victron which work great. I also installed the Amp-L-Start unit which keeps my chassis battery charged. They recommended that I install a switch to turn it off while driving to eliminate any conflict between the DC-DC charger and Amp-L-Start. I did install the switch, but only turn it on when I am parked at home for a few weeks.

**creativepart** · 06-06-2023, 09:45 AM

Quote:

Originally Posted by DustyDude

I also installed the Amp-L-Start unit which keeps my chassis battery charged. They recommended that I install a switch to turn it off while driving to eliminate any conflict between the DC-DC charger and Amp-L-Start.

Really? I don't remember that recommendation with mine.

Since the Amp-L-Start only charges the chassis battery when the voltage of that battery drops to 12.5v or something like that - and when driving the alternator is always putting out 13 or more volts. So, it seems that there couldn't be such a problem, but maybe I'm thinking about it all wrong.

The owner, developer, seller of the Amp-L-Start died suddenly within the past year. So, the product is in limbo right now and isn't being sold. I "hear" on other forums that this is temporary and someone else will pick up the product. I don't know if this is so or not. Ironically, the company is here in San Antonio operating out of a house in a suburb and a warehouse in another part of town.

DustyDude · 06-06-2023, 10:28 AM

Yes, they sold a little relay kit which would connect to your alternator and it would turn off the Amp-L-Start when the engine is running. I bought the kit, but then Joel told me that it may be easier to install a manual switch to accomplish the same thing which is what I decided to do. This is what he said:

"This avoids any chance of the AMP-L-START and DC-DC charger "fighting" with each other while the motorhome is being driven."

**creativepart** · 06-06-2023, 10:34 AM

Thanks for that. I may have to do the same thing. What kind of switch did you install? Something at the input wiring of the Amp-L-Start? I mounted mine on the removeable panel in front of the disconnect solenoid where the BIM used to live.

Actually, my OEM BIM is still there and still installed to everything but the House/Chassis wires. I just unbolted the spades for each and freed the BIM so I could lay it down in the cavity behind. I left it connected to all the other connections in case some future day when I wanted to reconnect everything.

DustyDude · 06-06-2023, 10:43 AM

Joel recommended that I install a switch on the negative side of the Amp-L-Start which will disconnect the ground connection. I mounted my Amp-L-Start in the battery bay under the steps so I drilled a small hole in the side wall of the recess between the floor and the top step and installed this waterproof switch:

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

The switch is far enough back so we don't kick it, but I can see it when I am entering the motorhome.

**creativepart** · 06-06-2023, 10:46 AM

I wish there was more info on the problem this solves. Joel invented the product so he should know. But with his passing... who knows???

DustyDude · 06-06-2023, 10:50 AM

Yes, he was not real clear, but the fix was cheap and easy so I thought better safe than sorry.

l1v3fr33ord1 · 06-06-2023, 02:40 PM

Quote:

Originally Posted by DustyDude

Mark,
I have been reviewing the documents you linked, but kept getting lost.

I'm with you. The "new style" 12 volt diagram is much harder to read/follow than the "old style!" I can help you work through it, if you wish. But, the info I gave in the post should be enough to get you going.

tim myers · 06-09-2023, 10:24 AM

Quote:

Originally Posted by DustyDude

Thanks for your reply. I assume removing this wire would also disable the Boost function as well. Or, are you saying that this wire would only impact the charging while the engine is running?

The battery isolation solenoid does two things, charge your house batteries from the alternator and combine both battery banks when the boost switch is pressed (momentary contact).

My plan is to put a switch in the line that powers the coil of the isolation solenoid, and in the line from the chassis battery and the dc to dc charger. The switch on the coil voltage line will remain open most of the time and basically just turn the isolation solenoid into a terminal. run a wire from the chassis connection side to the dc to dc charger input then run a line from the dc to dc charger output to the house side of the solenoid.

If you need the boost function open the switch feeding the dc to dc charger and close the switch on that powers the solenoid coil. Use your boost switch then revers the switch positions.

Rather than run wiring and installing a switch in the motorhome that could accidentally be triggered, I was planning to just put the switches behind the generator access hood. Your configuration may dictate a different location. I even considered a 2p2t switch to handle both wires.

DustyDude · 06-12-2023, 10:43 AM

I finally had time to look at the solenoid and it appears that it only has 3 posts and is designed to let power flow from the alternator to the house batteries anytime the alternator is generating power. Based on this, I don't think Mark's suggestion of just removing the KE wire will work in this situation. Plus, I never could find that wire anyway.

I ended up removing the short cable between the solenoid and the rely (battery disconnect?) and all appears to be working as intended. The red cable with the yellow shrink wrap connects directly to the house batteries (via a fuse) and I assumed the power flowed one way, but it turns out this connection also provides power to the coach DC circuit breakers as well. The coach now has DC power like before, but the batteries are only being charged through the DC-DC charger (with engine running) and does not put too much strain on the alternator.

I have ordered a cut-off switch so I can reconnect the solenoid to the relay in case I ever need to use the Boost function to jump a dead chassis battery. These are some pictures of the solenoid before and after removing the cable.

jipper · 06-17-2023, 09:32 AM

A few years ago I changed out my Batteries to the Lithionics on my 2019 Navion.
I installed a B to B in place of the short jumper cable between the Boost Solenoid and the Battery Disconnect. I also ran an additional jumper cable through a disconnect switch to reinstate the boost function if needed.
The B to B I used, (Kasie) has a current detection capability so I added a switch to the LR wire after the boost switch. The LR wire takes either the alternator running signal or the boost signal to the Boost Solenoid. This way I can shut off the Alternator charging to the B to B when I do not want charge the house batteries.
I also have a Amp L Start with a switch on the ground to prevent a short when the ground disconnect for the chassis battery is being used. I was servicing with the disconnect unplugged when I noticed that the Cab lights were working. Now when servicing I shut off the Amp L Start switch.

Jipper
2019 Navion J