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Old 02-04-2023, 11:06 AM   #1
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Question Can LFP batteries be used to start generator?

Replacing coach lead acid batteries with Lithium iron phosphate.
Can they start the generator without damaging the BMS?
How to isolate?
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Old 02-04-2023, 04:33 PM   #2
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Without any information about the year, model and floor plan designation it’s difficult to respond to the how to isolate question.

Many RVs use the chassis batteries to start the generator, not the house batteries. But don’t know enough info to advise you.

As to LFP batteries starting the generator… it depends on the battery and what their manufacturer says about it.
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Old 02-04-2023, 05:05 PM   #3
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I have a 200AH LiFePO4 house battery and it starts my diesel generator without any problems. The generator pulls about 165 amps when starting.

It depends on the generator you are trying to start but if similar to mine I donít think it would be an issue as long as you have at least 200 AH of battery.
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Old 02-04-2023, 05:21 PM   #4
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Hello!
I appreciate your response!
It is a 2019 Winnebago Outlook 25J.
The coach batteries are under the steps.
I'm fairly certain that the coach batteries are used to start the generator.
There also is a momentary crossconnect button in the cab in case the chassis battery goes dead you can use the coach batteries to start the engine. This is what I want to isolate because
the LFP battery manufacturer communicated that the LFP batteries are not to be used for engine starting.
So with that knowledge, the question is how do I set up the chassis battery to use it for the generator start, or how do I isolate a secondary small AGM battery for the generator starting duty?
I am unable to locate a detailed 12v wiring schematic at Winnebago.
Any help is much appreciated.
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Old 02-04-2023, 05:43 PM   #5
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Momentary tying the batteries together is not an issue but they should be either isolated or have a current limiting BIM or the alternator could be damaged during normal operation.
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Old 02-04-2023, 06:19 PM   #6
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I am unable to locate a detailed 12v wiring schematic at Winnebago.
how do I set up the chassis battery to use it for the generator start, or how do I isolate a secondary small AGM battery for the generator starting duty?
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Old 02-04-2023, 07:52 PM   #7
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Really detailed drawings stopped at 2010 model but we may have enough to get what is needed on this one?
First let me state that this is not something I've looked over or done as I do not use lithium at this point and that leaves some things like charging that I have not studied or given much thought. Be warned to study any details beyond the simple location and moving of cables???

This drawing if you want to go direct for more detail:
https://www.winnebago.com/Files/File.../000124121.pdf

Winnebago does add tape markers at the battery cable ends to help ID them.

Looking at this drawing it does look like the generator start cable is currently on the field side of a battery disconnect relay as I've marked in green. If one were to move that cable over to the left side of the solenoid and lay it on with the starter cable marked in red, I believe that is a simple way to change which battery does the generator starting??
This solenoid is what connect coach and start battery together when pushing the boost switcch or when engine running.

Click this snip to get a better view or go direct to get more detail.
Again, This is info based on what I see, far less than what might be needed!!

Click image for larger version

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Old 02-05-2023, 06:32 AM   #8
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You should be aware that if you move the generator starter cable over to the chassis side, you will probably set it up so that both the chassis and the house 12 volt supplies will be necessary to start the generator. Even if the chassis battery is fully charged, the start signal is probably being supplied by the house battery after you swap the cable.
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Old 02-05-2023, 08:08 AM   #9
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Good point to check as possible and not something that I am aware of on the reduced drawings that we get for that year.
One of many details that I am not sure of!!!

Looking back further in the drawings to years that have full schematics online can be a clue. On this one going back to the 2009 model does show it gets more difficult as the generator part of the controls go on the monitor panel and that is fully connected to the coach battery supply, making seperating them much more complex than just moving the main generator starter solenoid over.
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Old 02-05-2023, 09:57 AM   #10
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Thank you Morich!
These drawings will help a bunch.
At least I can start studying what is there in the 2019 model and see what may or maynot have been changed.
I appreciate your help.

Dave
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Old 02-05-2023, 09:59 AM   #11
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Thank you eyecando!
You make a valid point.
Further investigation is warranted.
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Old 02-05-2023, 10:44 AM   #12
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Thinking through a bit, it may not be a major problem---or not!
Not real world experience, so consider it guessing but if the controls are left on the coach battery for ease, this "might" be okay?

One issue is the controls for starting/stopping are on the monitor panel and might be hard to change, but the question I might have is what that would do?
Say the coach battery powers a switch that controls the solenoid on the generator starter . That is just a coil in that solenoid that feeds battery through the coil to ground.
That coil is seperate from the contacts of the solenoid, so does it create any problem if the power on those contacts is from the chassis batttery?

That would seem to need some assurance about how both work on the generator itself but the idea of two seperate power sources is what we often have on lots of solenoids. In fact the ignition switch on most cars use something similiar as a way to use small wires/contacts on the ignition key to move a solenoid where we can use great big battery cables to do the work of turning the starter.
Therefore called --"slave relay" as the little guy makes the big guy do all the work!

Too many points that I'm guessing but not fully saying it is okay!
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Old 02-05-2023, 02:21 PM   #13
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Well,
It's crossed my mind that maybe it will be possible to try and isolate the LFP batteries and put a small AGM battery ouside of the existing battery box and swing the generator starting cables to it. Seems like there are small portable jump packs that pack enough oomph to be able to start truck engines. Anyway there are many questions that remain unanswered at this point.
Lots more investigating and probably a bit of trial and error before all questions will be answered.
I truly appreciate your sending the schematics and sharing your knowledge and opinions.
I hope to get back to the project soon... Mother nature seems to like sending MN cold and snow.
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Old 02-05-2023, 03:21 PM   #14
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My RV… which is different than yours… has the generator start connection on my house battery disconnect solenoid and I have 2-200 amp hour Renogy LFP house batteries. Before I installed the LFP batteries there was a BIM between the two disconnects. I simply removed the BIM between the disconnects.

I was worried about the generator starting from the house batteries but it has not been an issue. This may be the case because of the 400 amp capacity able to output 200Ah or not I’m not sure. But as I say I’ve not had any issues.

I might add… with the LFP batteries, I start the generator far less than previously. Mostly now it’s when I exercise the genset monthly when in storage.
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Old 02-05-2023, 03:37 PM   #15
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Along the same lines, you will likely want to remove any latching solenoid that connects house and chassis to your alternator. This what I had to do when I removed the BIM between the house and chassis disconnects.

With this removed you lose the ability to bridge both battery banks for Auxiliary starting, but it protects your alternator by not allowing it to charge your LFP batteries. And you will probably want to install a DC to DC charger to charge the LFP batteries while driving.

Precision Circuits makes a battery isolator made for LFP batteries that takes the place of your current latching solenoid that might work great for your installation. It preserves all of your current functionality and protects your alternator by turning on and off as you drive.

If this works for you it might solve many issues.

https://www.precisioncircuitsinc.com...i-BIM-Rev1.pdf
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Old 02-05-2023, 04:23 PM   #16
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Maybe pointing to a couple sites for info is good?
When the snow is hub/ axle deep is a good time to stay inside and dream, so looking at drawings can help to avoid crawling under!
Parts here is an interactive site in that we can look from any angle and turn things all around to study what they say is there!
https://catalog3d.winnebagoind.com/2019/324585.htm

Then a couple tips for use if new to this plan? Once you have sorted to electric and this is in the chassis wiring, go to one of the views listed at bottom right for front/back/left/right, etc and turn the RV so you may spot the batteries?
To keep it centered on any specific point go to bottom left to the cross looking symbol, clip it, then on the part to keep centered.
In that way it should stay centered as you scroll to zoom or drag the mouse to turn.

Once learning to drive, avoid getting dizzy! But there is a ton of good stuff there as the drawing are very detailed and you can spot the parts if you know what they look like. Or if you know the name, go to the list at right and click something like the solenoid and it will flash or turn yellow on the drawing helping to find things you know thw name but not where what it looks like! Repeating clicking flashes yellow on drawing!

So what I see is the solenoid, etc. loooks like it matches for 2009 to past 2013!!! Yeah! possible to use the early drawing if it looks all the same?

Click this snip to view better/larger but it looks very much like what I posted earlier, so look to see if it does really match?
electrical drawing for 2009
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Parts drawing for 2013
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I've been without commercial power and the yard is too messed up to want to look, so I know about staying inside!!
View from the porch!

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And my response?
Click image for larger version

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Old 02-05-2023, 07:27 PM   #17
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Quote:
Originally Posted by Morich View Post
Thinking through a bit, it may not be a major problem---or not!
Not real world experience, so consider it guessing but if the controls are left on the coach battery for ease, this "might" be okay?

One issue is the controls for starting/stopping are on the monitor panel and might be hard to change, but the question I might have is what that would do?
Say the coach battery powers a switch that controls the solenoid on the generator starter . That is just a coil in that solenoid that feeds battery through the coil to ground.
That coil is seperate from the contacts of the solenoid, so does it create any problem if the power on those contacts is from the chassis batttery?

That would seem to need some assurance about how both work on the generator itself but the idea of two seperate power sources is what we often have on lots of solenoids. In fact the ignition switch on most cars use something similiar as a way to use small wires/contacts on the ignition key to move a solenoid where we can use great big battery cables to do the work of turning the starter.
Therefore called --"slave relay" as the little guy makes the big guy do all the work!

Too many points that I'm guessing but not fully saying it is okay!
The generator will start with the chassis battery connected to the generator and the generator start circuit (monitor panel) connected to the house battery. The only issue is that if either battery is dead, the generator will not start.

Both batteries must supply sufficient voltage and current. This doubles the possibility of not being able to start the generator due to a dead battery when you need it the most.
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Old 02-08-2023, 07:09 PM   #18
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Quote:
how do I isolate a secondary small AGM battery for the generator starting duty?
. I have used the U1 garden tractor type of AGM to start outboard motors up to 25 HP. One is small, not that expensive, and would easily start the 4,000 watt Onan which apparently comes with your coach in an emergency/or even on a regular basis, if you have a way to keep it charged.
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Old 02-09-2023, 09:03 AM   #19
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Thanks to all for thoughts and considerations.
I will be using every idea as I move forward with the conversion.
When completed I hope to share the results for anyone interested.

Dave
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