Skip to main content ↑ ↓
Topic: Adding a switch to the starting battery circuit?? (Read 264 times) previous topic - next topic

Adding a switch to the starting battery circuit??

There's hopefully a simple answer.    I'm using three 800 ccs battery's for starting my 8.3.  Can I add a switch to the circuit? 
  Reason why?  Two years ago I had a Lithonics device installed to replace the isolater and act as boost option and safely charge my lithium batteries. Seems to work fine the lithium side but doesn't always keep the engine batts charged.
 So I connected an automatic trickle charger but Lithonics device must trip it when it does charge them. So... thought I would add a cut off switch , then the trickle charge wouldn't be interrupted but I'm betting the collective amazing intelligence of this group will tell me I can't do that. 

I do see that there's two positive leads coming off those engine batteries so one must be the starter and the other must be for all related power needs
( lights power plugs and key activated stuff) so maybe I should just switch that one ??

 So question is A. Can I switch the whole thing and how big ( amperage ) or B. should I just switch the alternate feed for other stuff      And how big. I'm guessing 300 amp would work.
Robert and Susan
 1995 36' 280 WTBI 8.3 3060r
 1200 watts on the roof, 720 Ah of lithium's
 Build # 4637. Motorcade # 17599
        FMCA  # 451505
        18  Wrangler JLUR

Re: Adding a switch to the starting battery circuit??

Reply #1 –
What you really need is to have the Lithonics device only try to activate when the engine alternator is producing power. Usually there is an input to enable it for that application. If not, then you want a control relay, or some means that it only gets connected to the chassis batteries when the engine is running. This approach would also allow you to restore the operation of the boost relay, which could then be used to charge the chassis batteries from the house batteries as originally designed. 
Dennis Haynes
Bohemia NY
2008 Nimbus 342 SE Carlyle
Build #6475
Motorcade #19148

Re: Adding a switch to the starting battery circuit??

Reply #2 –
So I'm hearing that leaving the boost switch on is one option.  I actually knew that... but I realize there's the fear of discharging all of the batteries together. Thing is we're plugged in most of the time these days so there's little chance of that. 

 Now that I think about it. It's only an issue when we are on the pole. So maybe that Lithonics device isn't designed to back feed from the lithium batts.

 Still curious about the switching thing though.  Trouble is, me and electronics, not so much but I'm tryin.
Robert and Susan
 1995 36' 280 WTBI 8.3 3060r
 1200 watts on the roof, 720 Ah of lithium's
 Build # 4637. Motorcade # 17599
        FMCA  # 451505
        18  Wrangler JLUR

Re: Adding a switch to the starting battery circuit??

Reply #3 –
No, the Lithonics device does not reverse charge the chassis battery from the house batteries. There are very few DC to DC chargers that include that function. Also, if charging the chassis battery from any source, especially the boost circuit, it again has to be disabled. If not, it will basically become a heater as current is just going around in a loop.

With a properly sized, matched battery bank the original alternator/diode set up works quite well with lithium batteries.  I would have upsized the alternator to take the load.
Dennis Haynes
Bohemia NY
2008 Nimbus 342 SE Carlyle
Build #6475
Motorcade #19148
 

Re: Adding a switch to the starting battery circuit??

Reply #4 –
Robert & Susan, Yes simple answer. . . Sounds like your coach has a dedicated battery cable to the starter solenoid. Remove the other battery cable, connect it to an Amazon Ampper battery disconnect switch. And connect a short cable from Ampper to the battery.

If no other cables are connected the starter solenoid batter cable terminal, turn switch off and chassis battery is isolated, something worthy to have for many different reasons.

High-amp starter current will not have to be disturbed, and several-hundred amp disconnect will be okay without starter current load.

Hopefully you don't have OEM chassis battery cables that only have a battery post terminal. We recommend all to use heavy-duty Military battery post terminals and connect all cables with bolt and nut. When a battery post end weakens or fails, just replace the terminal and not the cable. While at it, connect coach ground cables to one of the three batteries and positive at the third battery, with some way to connect all batteries in parallel with short loopy cables or better with a metal bar across all three Military battery posts.

Hope this answers your question.