Splitting up the batteries and charging

[Vintage465]

I want to install a second battery dedicated to running the forced air furnace. I know there are going to be a lot of suggested alternatives like generators, catalytic heaters, rent a space with hook-ups, more covers on the bed etc. But suffice to say, I want to be able to run the existing Forced Air Unit(FAU)while boon docking w/o having to fire up a generator. I am going plan on adding a second battery and connect the charging up to the existing Samlex 300w/30a system. I will tap into the existing 8 gauge (8ga) wire and then add two disconnects downstream of the tap. That way I can either charge the "Coach Battery" or the "FAU Battery". Couple questions. Currently I run two 6v in series. Makes me think the second battery for the FAU should also be two 6v in series....thinking I read somewhere that you shouldn't mix one 12v with two 6v in series? Also, related, but not really detrimental to the entire situation is that I will almost certainly add one more 150w Samlex panel to get me 450w of charging. Other than personal preference, does anyone see anything really wrong with my tentative plan? I attached a little sketch plan.

[Vintage465]

So I did a pretty darn thorough maintenance of the two 6v Interstate Batteries on the trailer. They are right at 2-1/2 years old. They've been run flat three times. By flat, mean they would not light up a test light...........pretty darn flat. When I checked them out at the earlier part if the year I had them unhooked from the coach, charged them fully, let them rest and they all had good cells according to the hydrometer. Today there was some corrosion, but not bad, and all connections solid. They seemed to be fully charged at 13.31 volts, but one cell in each battery measured below the "good" and was in the "fair" zone of the hydrometer. It was on the upper side of fair, but definitely not in the green. When I hooked a charger up to the battery, it says the batts are full and the needle just bounces around like it does when the battery is fully charged. The only other place to look is where the 8ga. wire goes to the "line" side of the converter and I found that the lug where the 8ga. wire connects was loose. Not sure if it was loose enough to cause the issues I experienced last week end, but I'll tell you, it was anything but tight for sure.

We are heading out for a week toward northern California Coast next Friday and I will see how the dude works with the lug tightened.

[doughere]

MrWizard wrote:
You will have to isolated the furnace circuit
12v hot and ground of the heater from the fuse box, and attach to the new battery

To me it makes more sense to just double the size of the current bank by adding the new battery
Instead off trying to sperate circuits , using one battery for just the heater and having to charge them separately

I'm with this.

Follows all the KISS principles (keep it simple S#$%&*)

Doug

[time2roll]

The plan is fine. However I agree with the others to just make one battery and use it as such. With all the manual switches it sounds like a pitn to manage and I speculate in time you will get bored and just leave it all connected as a group of four.

To truly isolate the second battery set I recommend a battery combiner such as a BIRD relay.

With the additional solar charging all as a group... you can always separate later if you really feel the need. What is missing in the analysis is the actual voltage during charging and discharge conditions. Also when you think the batteries are charged check them once with a hydrometer.

With all together you do gain some capacity due to the Peukert effect.

[valhalla360]

westend wrote:
I don't see any of the dreaded draining or capacity loss that some theorize.

If the old batteries are in good shape, you likely won't have any problems.

Since the OP is trying to fix a problem and there is a good chance it is related to the battery, best not to complicate things by introducing additional variables.

[westend]

I have two banks of batteries. one bank of 2 x 6V's and another with 3 x agm 12v's. I have a multi-switch distribution panel that I built that can separate the two banks between converter, inverter, and solar charging. For the last few years, both banks have been interconnected and primarily charged from the solar controller. I don't see any of the dreaded draining or capacity loss that some theorize.

I don't have any worries about the furnace draining batteries since I use a propane space heater that doesn't use electricity to operate. I do have a 120V fridge and that is the biggest draw among the various devices I power.

I'd suggest to interconnect another pair of 6V's to the 12V system and monitor charging/draw. If you have a battery monitor and a more sophisticated solar controller, it's a piece of cake. Having all the 12V power interconnected will afford more power (Peukert) and result in lower cycling level draw-down (batteries last longer).

[valhalla360]

Vintage465 wrote:
Gordon Three and Drew,
I've noticed when the heater is running on a cold evening, then we have a couple lights on and turn on the water, the lights dim and the heater fan slows. This would leave the heater alone when we mess with other 12v draws. Also, on a real cold night, say 20-30 degrees and the heater cycles through out the night and pulls the battery down to say 40%, I will wake up to nice bright lights and easy running pump. Really that's the whole idea.

Based on what you describe, something is wrong beyond the size of the battery bank. Nothing you describe should overwhelm a charged bank to the point that the batteries dim.

One possibility is your current bank is near the end of it's life. If you are regularly pulling it down to 40% (or more), that's hard on the batteries.

Another possibility is bad wiring or connections. Under light loads it's OK but when pushed a little bit, the corrosion on a bad connection limits the amps that can flow and you see diming as the various loads compete for the limited amps.

A single house battery bank is generally best. Google the peurket effect. A single large bank can absorb more power more quickly and will allow greater overall discharge compared to two smaller banks of equal overall size. The exception would be if this is a MH and you want to keep the engine starting battery independent, so you can always start the motor.

First step would be to check the batteries.
Next would be to pull the connections apart clean them and put them back together.

One catch particularly if you have been hard on the current batteries is if the new ones are in any way connected, the old ones will try to constantly pull power off the new ones. It's best to install battery banks at the same time.

[Vintage465]

GordonThree wrote:

Vintage465 wrote:

GordonThree wrote:
Another 2x 6v batteries should cure those issues. A battery drain protector between the bank and the furnace will stop it from draining too much from the bank.

Have you switched your lights to LED yet, preferably the kind with built in regulators?

We have all LED lights in our trailer from the factory.

Something's wrong with a connection then, as another poster previously suggested. Have you separated the batteries and checked cell volts after a good charge and rest?

I charged the batteries up fully, checked them with a hydrometer around March-ish 2017. They were solid at that time. I will do a little follow up before my next outing in 2 weeks, but my guess is all is good and I just want better. But, won't really know till I remove the battery cover and check/clean the connections and test the cells. Do that this week and get back to y'all.

[GordonThree]

Vintage465 wrote:

GordonThree wrote:
Another 2x 6v batteries should cure those issues. A battery drain protector between the bank and the furnace will stop it from draining too much from the bank.

Have you switched your lights to LED yet, preferably the kind with built in regulators?

We have all LED lights in our trailer from the factory.

Something's wrong with a connection then, as another poster previously suggested. Have you separated the batteries and checked cell volts after a good charge and rest?

[Vintage465]

GordonThree wrote:
Another 2x 6v batteries should cure those issues. A battery drain protector between the bank and the furnace will stop it from draining too much from the bank.

Have you switched your lights to LED yet, preferably the kind with built in regulators?

We have all LED lights in our trailer from the factory.

[MrWizard]

You will have to isolated the furnace circuit
12v hot and ground of the heater from the fuse box, and attach to the new battery

To me it makes more sense to just double the size of the current bank by adding the new battery
Instead off trying to sperate circuits , using one battery for just the heater and having to charge them separately

[DrewE]

The dimming/slowing may just be not the best connections between the battery and the rest of the RV. Obviously the battery voltage will depend on the load to some extent, but a somewhat high resistance connection will exacerbate that.

If you have twice the total battery capacity and the furnace is using 60% of your capacity currently over the course of a night, it would only use about 30% after the upgrade and your lights would still be decently bright.

I don't mean to suggest that there's any inherent reason why it's impossible or unworkable to have a separate battery for the furnace, it's just I don't see any benefit. (Intriguingly, my house--and several others of the same general vintage--is wired much like what you're proposing. I have two independent 100A electric panels side-by-side in the garage, connected to the electric meter, originally one for electric heat and one for other things. Over time the separation of loads has become a bit mixed, with some non-heat loads now on the heat panel, but that was the original setup. I'd slightly prefer a single 200A panel given the choice.)

[azrving]

Huumm. Not that it's probably a lot more wire but more wire and more connections equal more resistance in theory. Drawing one battery down with x amount of amps vs spreading it over twice the amount of battery may reduce the Peukert effect. May be splitting hairs. One blue seas rotary switch can separate batteries 1/2/both positions.

[GordonThree]

Another 2x 6v batteries should cure those issues. A battery drain protector between the bank and the furnace will stop it from draining too much from the bank.

Have you switched your lights to LED yet, preferably the kind with built in regulators?

[Vintage465]

Gordon Three and Drew,
I've noticed when the heater is running on a cold evening, then we have a couple lights on and turn on the water, the lights dim and the heater fan slows. This would leave the heater alone when we mess with other 12v draws. Also, on a real cold night, say 20-30 degrees and the heater cycles through out the night and pulls the battery down to say 40%, I will wake up to nice bright lights and easy running pump. Really that's the whole idea.