How to keep the starting battery charged?

[Ave]

I recently bought a used class c Jayco that had solar panels and Lithium batteries installed. I know that it's unwise to simply use the stock battery combiner (my phase) to allow the starting battery to be charged from the solar panels since the Lithium batteries charge at a higher voltage and a lead acid battery wouldn't be happy with long term charging at that voltage level. The combiner isn't being used at this time. I know that there are devices that will allow the alternator to charge the Lithium batteries but I haven't seen the reverse.

I'd pop in a buck converter except they usually require a voltage difference of 2 volts between load and source. So what does one do to keep the starting battery up? The previous owner used a portable 25 watt solar panel and controller. I'm looking for a better solution.

Thanks,
Jim.

 

[Mark_K5LXP]

Is your only power source the solar panel? Otherwise I'd just say to get a $35 battery tender and check the box.

You can get a maintainer like the trik l start that will take power from your house battery (12-18V) and provide a controlled charge rate to your chassis battery. But if your sole power input is a solar panel then it's that much less power available to the house side, if that matters. If solar goes away or it can't keep up (for any number of reasons) then you end up with both house and chassis side going down.

Most direct and foolproof is to use a cutoff switch or lift a cable off the chassis battery. Nothing to buy, nothing to go wrong.

Mark B.
Albuquerque, NM

 

[Gary RV_Wizard]

Sound advice from Mark. Don't overthink the chassis battery charging problem, especially if you don't stay on solar power alone for weeks at a time. An automotive starting battery routinely sees 13.6v-14.4v from the alternator and lives many years, so some higher voltage is not a disaster. Even 14.6v isn't too much as long as it is not sustained for several hours at a time.

Odds are your existing battery combiner would do the job nicely, stealing some power from the house battery bank to provide a float charge to the chassis (starting) battery. As long as you can afford the small load on the house batteries, that's the simple way to do it. Another would be to plug a battery trickle charger (maintainer) into on inverter powered from the house batteries. Maybe put it on a time so that it only runs a couple hours each day.

 

[uchu]

Here's a setup similar to what you're thinking:

Charging Chassis Battery from Solar - Page 2 - Forest River Forums

So here's what I did. Purchased a 10 pack of 8 AWG 5/16 hole wire lugs from Amazon, torch soldered 3 mm female (electric motor RC airplane) connector to lug for each end. Purchased 15A manual reset

www.forestriverforums.com

 

[Ave]

Is your only power source the solar panel? Otherwise I'd just say to get a $35 battery tender and check the box.

You can get a maintainer like the trik l start that will take power from your house battery (12-18V) and provide a controlled charge rate to your chassis battery. But if your sole power input is a solar panel then it's that much less power available to the house side, if that matters. If solar goes away or it can't keep up (for any number of reasons) then you end up with both house and chassis side going down.

Most direct and foolproof is to use a cutoff switch or lift a cable off the chassis battery. Nothing to buy, nothing to go wrong.

Mark B.
Albuquerque, NM

I'm thinking about the cutoff switch for when it's parked. I have a 2000 watt inverter/converter that give me 12 volt power when plugged into the mains. When the sun is shining is suspect the converter isn't doing anything most of the time, but overnight it'll run whatever load is present. Since the combiner isn't in the circuit the alternator isn't charging either. Since the chassis battery drives things like the radio and a couple of lights and the step, I don't want to disconnect it when we're using the rig. There are 800 watts of solar and two 100 AH batteries and of course a generator, so I don't think I'll be without some sort of power.

 

[Krazeehorse33]

How long are you planning on leaving it sit without starting? Unless I’m missing something it sounds like you have a non issue. Plus you should have a momentary switch to allow you to start off the house batteries if necessary for a “plan B”.

 

[Ave]

Sound advice from Mark. Don't overthink the chassis battery charging problem, especially if you don't stay on solar power alone for weeks at a time. An automotive starting battery routinely sees 13.6v-14.4v from the alternator and lives many years, so some higher voltage is not a disaster. Even 14.6v isn't too much as long as it is not sustained for several hours at a time.

Odds are your existing battery combiner would do the job nicely, stealing some power from the house battery bank to provide a float charge to the chassis (starting) battery. As long as you can afford the small load on the house batteries, that's the simple way to do it. Another would be to plug a battery trickle charger (maintainer) into on inverter powered from the house batteries. Maybe put it on a time so that it only runs a couple hours each day.

I like the trickle charger idea. I have a small inverter I could use. I'll give that a try.

I hear you wrt the chassis battery seeing >14 V from the alternator but your qualification "as long as it is not sustained" seems to suggest that I shouldn't leave the combiner on full time. I don't think I have any control over it except to disconnect it and that's a pain.

 

[Ave]

How long are you planning on leaving it sit without starting? Unless I’m missing something it sounds like you have a non issue. Plus you should have a momentary switch to allow you to start off the house batteries if necessary for a “plan B”.

There's enough parasitic load on the chassis battery to run it down in a few weeks. While I agree that there is supposed to be the switch to assist starting, I haven't found it yet. I don't like for lead acid starting batteries to discharge very far. They aren't as resilient as a deep discharge battery.

Thanks to everyone for the advice
Jim.

 

[Gary RV_Wizard]

I hear you wrt the chassis battery seeing >14 V from the alternator but your qualification "as long as it is not sustained" seems to suggest that I shouldn't leave the combiner on full time.

I'm thinking "sustained" is measured in days rather than hours. Besides, your solar isn't charging 24/7, so likely seeing the higher voltage only a few hours each day.

A relatively smart combiner like the Magnum SBC or Xantrex Echocharge or even the Trik-L-Start is going to avoid excessive charging anyway.

 

[Mark_K5LXP]

Two ways to approach a problem like this is to increase the input to, or decrease the output from the chassis battery. The common solutions are more about charge maintenance during storage than operating loads. An inverter powered maintainer will be a fairly inefficient solution but would work, if you have the power to burn. It certainly wouldn't hurt to use a maintainer but if you're running a lot of loads it might not keep up so a proper charger might be more appropriate. Something I would think about is moving some of those loads over to the house side, and minimize the load on the chassis battery. That kills both birds with one stone, the chassis battery won't go down and you don't have to mess with a charger.

Mark B.
Albuquerque, NM

 

[JayArr]

I leave my cars parked for months and they still start. I think you're chasing a non-problem. If you're doing this because you like gadgets and want a project then a small inverter hooked to a battery tender should work.

If you're really worried about it I'd just start the engine once a week. That's free.

 

[Ave]

I also have left cars for months with no problem. This isn't a car. It has parasitic loads that will and do run the battery down. I really don't like to draw a starting battery down very far since it will reduce the life of the battery. Since I understand the TV uses the car radio for audio, I'm worried that running the TV at night will put too much of a load on the chassis battery. Someone mentioned moving the load to the coach batteries but that may be easier said than done.
I can and will disconnect the chassis battery when parked but when on a trip, I can't really do that.

thanks,
Jim

 

[Skookum]

Another vote for just hook a battery tender to the chassis battery. And pro-tip, if your cars sit longer than about 10 days it's good to hook them up to a battery tender too. Batteries that just sit will sulfate, which isn't good for them either. And they also will lose charge.

In many motorhome models, Jayco is tying both chassis and house power into the in-dash radios in C's and Super C's. So with the ignition off and your TV using the chassis stereo/speakers to play sound, have you verified from where it's actually getting power?

 

[richconn]

Trickle start. Lslproducts.net

 

[Non-partic]

For storage, I would think you can just disconnect your your LiFeP04 battery bank and let it discharge 1-2%/month and you will be fine when you pick it up next season.

That will leave your L-A battery bank being charged off your solar controller and it has charging algorithms that will keep you your flooded L-A batteries full, but it will probably find your cells a little low on water when you pick up your RV next season.

In my RV, I installed a Keyline Voltage Sensitive Relay (VSR) to join and isolate my house batteries with my engine batteries and this has worked very well to keep both charged.

My preference for maintaining both my engine and house batteries, since there is a VSR joining and isolating them, is to add a Victron IP67(bluetooth) AC charger that works fantastic and I like the bluetooth app so I can look at my charging profiles on my cell phone.

https://www.amazon.com/dp/B07TJK3X71/ref=sspa_dk_detail_8?psc=1&pf_rd_p=d533dd31-f352-432f-87d0-ace6fec162b4&pf_rd_r=MYRHFVS0HFJFHD0V8320&pd_rd_wg=aAO8j&pd_rd_w=UXCw1&content-id=amzn1.sym.d533dd31-f352-432f-87d0-ace6fec162b4&pd_rd_r=98e264dd-ec95-45cf-bdaa-644e44950a0c&s=automotive&smid=AERMGYAT5R869&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExSFBYMElBMTJRVlkxJmVuY3J5cHRlZElkPUEwNDUyODI2Mk4xVkxCOVZIREFGSCZlbmNyeXB0ZWRBZElkPUEwMzA2NDYzMlFJSUY2NlA0VFFQRSZ3aWRnZXROYW1lPXNwX2RldGFpbF90aGVtYXRpYyZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=

Note: This Victron is now my primary RV charger and I turn off the charger function inside my Inverter/Charger. It also works fine with the solar controller.

If you have LiFeP04 batteries and L-A batteries, I would think you would be better off using a separate battery charger, but someone else with more experience than I have can comment more on this.