ADDING AN AUXILLARY DC POWER SOURCE TO THE FURNACE

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ADDING AN AUXILLARY DC POWER SOURCE TO THE FURNACE

March 30, 2021, 08:08:36 pm

Has anyone added an alternate source of DC power to supplement running your furnace overnight, off-grid?

We are thinking of getting a Jackery Solar Generator (for example) to plug into the furnace wiring setup, as needed, as a backup to get us through a cold night if the house batteries run too low. If it's feasible to make such a hookup, has anyone tried it? I would like to have the Jackery-type power source on hand for my C-PAP machine but would like it to double as a backup for the furnace, too.

I've looked at Youtube videos on servicing a Suburban furnace. It showed four wires connecting it to the RV system. A red and yellow for 12VDC and two blue wires for the thermostat. Switching the red/yellow wires away from the RV to a 12VDC alternate source looks like it would work to me, depending on how accessible the furnace wiring is.

Thanks,
-Lance.

Re: ADDING AN AUXILLARY DC POWER SOURCE TO THE FURNACE

Reply #1 – March 30, 2021, 10:53:26 pm

The furnace draws about 6 amps, as I recall. Running it all night would use about 30 amp-hours, assuming a 50% duty cycle. Your house batteries have about 110 amp-hours of "safely usable" power--that is, power you can use repeatedly without jeopardizing their longevity too much. So if you can charge them fully by nightfall, you'd probably be OK with what you have now.

But let's take the portable powerpack case. 30 amp-hours at 12 V is 360 watt-hours. A Jackery 500 could supply that all by itself. Or it could run your CPAP all night, assuming you can get along without the hose heater and humidifier. (I do, but everybody's different.) It probably couldn't do both, though.

So yes, you could do this with a Jackery powerpack. But switching back and forth between two power sources, and charging up the powerpack every day, sounds cumbersome. I'd give serious thought to upgrading your house bank instead. You have a midbath, and there's a space under the fridge that is perfect for installing more batteries, if you go with AGMs (which need no outside venting). I'm not saying it will be cheap, but neither are the Jackery powerpacks. And you'll have a better system for your whole coach, rather than an awkward add-on for one or two appliances.

The Jackery powerpacks are great for tent or van campers who need an-all-in-one portable battery pack/inverter that can be charged at home and then taken out for a weekend. But your Lazy Daze already has a complete power system with a charger, inverter, outlets, and batteries. All you really need is to increase that battery bank's capacity. Unless you really require something self-contained with a handle you can lug it around by, it may make more sense to improve on what your coach already has.

Just a thought. :-)

Re: ADDING AN AUXILLARY DC POWER SOURCE TO THE FURNACE

Reply #2 – March 31, 2021, 09:23:08 pm

My thought is similar to Andy’s, throw one BattleBorn in and your situation is already improved, 2 would put you over the moon.

Re: ADDING AN AUXILLARY DC POWER SOURCE TO THE FURNACE

Reply #3 – April 01, 2021, 12:12:09 am

"throw one BattleBorn in and your situation is already improved, 2 would put you over the moon."

Let's expand upon that a bit. (As it happens, I have two Battle Born 100 amp hour LiFePO4 batteries fight now.)

First, just to be clear: you can't mix battery types (or even vintages, really). You can't just add a Battle Born lithium battery to your existing lead-acid batteries. Neither would be happy.

So... using the "20%" LiFePO4 rule of thumb--that is, for longest life, these lithium batteries should not be discharged below about 20% of their rated capacity, at least not on a regular basis--one Battle Born battery will give you 80 "safely usable" amp hours*. That's a lot less than the 110 safely usable amp hours you get from a pair of 225 Ah Trojan T105s or equivalent Lifeline AGMs. Two Battle Borns, on the other hand, would give you at least 160 usable Ah, and that's a big improvement over the Trojans or Lifelines. So if I were going to go the lithium route, that would be my minimum configuration.

* Battle Born says you can discharge their batteries to 100%, but since their LiFePO4 technology is not significantly different from that of their competitors, I choose to interpret that as marketing hype, and play it safe.

But it isn't just a matter of swapping in Battle Borns instead of your lead-acid batteries. LiFePO4 batteries need different charging voltages and schedules than lead-acid (flooded or AGM) batteries. The converter in a 2003 Lazy Daze, unless it has been replaced, will probably not be good for these expensive new LiFePO4 batteries. So you'd also want to upgrade to a converter that can be set up correctly for LiFePO4 batteries.

LiFePO4 batteries don't like hot temperatures (it'll shorten their lifespan), and when temperatures drop to freezing or below, they will stop allowing charging to prevent being damaged. So putting them in the same outside compartment where Lazy Daze put the house batteries isn't the best idea. Yes, you could insulate it, but that's still less than ideal. Fortunately, with a midbath, as I mentioned earlier, that compartment under the fridge is a perfect place to put batteries and keep them in a more temperate climate. You'll have to move some cables or make some jumpers, but it's not too bad.

Bottom line: LiFePO4 batteries have many advantages--faster charging, more usable capacity, lighter weight, and so on. I like mine a lot! But they are pricey, and although Battle Born markets them as drop-in replacements for lead-acid batteries, they really aren't... quite. You'll probably need to upgrade your converter, and you'll want to relocate the batteries inside the rig. I'd be the last person to discourage you from doing this, but on the other hand if you said "That's just too much money and trouble," I'd completely understand. A couple thousand dollars worth of Battle Borns plus a new converter add up to a lot more than the $500 Jackery powerpack you started off this thread by considering.

Re: ADDING AN AUXILLARY DC POWER SOURCE TO THE FURNACE

Reply #4 – April 01, 2021, 01:26:45 am

I would start by installing a battery monitor to determine if you are draining the batteries too deeply or if the existing system is adequate and if it has enough solar to fully charge the batteries daily.
Even if a Jackery is in your future, you need to keep it charged. There is no way to accurately measure the battery charge level without a true battery monitor, the LEDs on the hood's monitor panel do not show this.

If your 2003 LD had the solar option, you will have either one or two 85-watt panels, this isn't enough solar to recharge the coach battery that is used for a C-PAP machine. Increasing the solar to 400-watts or more is suggested along with changing to a Maximum Power Point Tracking (MPPT) solar charge controller, for maximum efficiency.
Increasing battery storage more complicated than just adding capacity.

Larry

Re: ADDING AN AUXILLARY DC POWER SOURCE TO THE FURNACE

Reply #5 – April 01, 2021, 12:15:10 pm

I'm kicking myself, because Larry brought up the very first thing I should have said: if you don't have a good battery monitor (e.g., Victron BMV 7xx series, or better still, Balmar SG200), how do you know whether you need auxiliary batteries? Maybe you're OK with what you have. Maybe you do need more batteries. Or maybe your batteries are adequate, but you need more solar panels to keep them charged, in which case adding batteries would be a waste of money. You just don't know.

Before making any decisions about add-ons, get a good battery monitor and watch your usage over a period of time, to see what if anything you need to add.

(About that Jackery Solar Generator kit you initially mentioned: Jackery's solar panels are not weatherproof, so if you did go that route, you'd have to bring them indoors at night, when leaving the rig, and in general whenever precipitation was a possibility. Better to get a more robust solar panel or panels, such as Renogy's rigid panels. Avoid flexible panels; they don't have a good record for reliability or longevity.)

Re: ADDING AN AUXILLARY DC POWER SOURCE TO THE FURNACE

Reply #6 – April 01, 2021, 01:38:26 pm

Quote from: Andy Baird - April 01, 2021, 12:15:10 pm

.

(About that Jackery Solar Generator kit you initially mentioned: Jackery's solar panels are not weatherproof, so if you did go that route, you'd have to bring them indoors at night, when leaving the rig, and in general whenever precipitation was a possibility. Better to get a more robust solar panel or panels, such as Renogy's rigid panels. Avoid flexible panels; they don't have a good record for reliability or longevity.)

A friend has a Jackery 1000, with the solar panel option, I was amazed that the panels were not waterproof, really, panels that must be sheltered from rain? This eliminates leaving them out when away for the day.
It's better to buy a high-quality suitcase panel kit that can withstand hard rain or permanently mount panels on the roof.

Larry

Re: ADDING AN AUXILLARY DC POWER SOURCE TO THE FURNACE

Reply #7 – April 01, 2021, 04:42:44 pm

Wow, thanks, guys. These are the comments I've been needing. Very much appreciated. I'm sure I'll have a few more questions but at the moment, I have one. I had occasion to replace the original solar controller with a Blue Sky Solar Boost 3000i. It has an Ah setting for the readout but it doesn't seem to function, unless I don't understand how it works. If it does function correctly, would that suffice as a battery monitor?
My understanding of the above comments: Add a monitor to see what's what first. Then, if adding more batteries, AGM's are simplest. They are fully compatible with existing factory equipment. Except I will need to upgrade the under-powered factory solar panels
Thanks again. -Lance.

Re: ADDING AN AUXILLARY DC POWER SOURCE TO THE FURNACE

Reply #8 – April 01, 2021, 04:57:51 pm

Quote from: Lance Echo-Hawk - April 01, 2021, 04:42:44 pm

I had the occasion to replace the original solar controller with a Blue Sky Solar Boost 3000i. It has an Ah setting for the readout but it doesn't seem to function, unless I don't understand how it works. If it does function correctly, would that suffice as a battery monitor?
My understanding of the above comments: Add a monitor to see what's what first. Then, if adding more batteries, AGM's are simplest. They are fully compatible with existing factory equipment. Except I will need to upgrade the under-powered factory solar panels

The 3000i is a solar controller, not a battery capacity monitor, it does not have an amp-hour setting. The 3000i will not provide the information needed on the battery's charge level.
Victron, Xantex and Balmar all sell battery monitors.
http://www.xantrex.com/power-products/power-accessories/linklite-battery-monitor.aspx
https://www.victronenergy.com/battery-monitors/bmv-700https://balmar.net/sg200-battery-monitor/
SG200 Battery Monitor - BalmarBalmar

Larry

Re: ADDING AN AUXILLARY DC POWER SOURCE TO THE FURNACE

Reply #9 – April 01, 2021, 06:05:38 pm

Quote from: Lance Echo-Hawk - April 01, 2021, 04:42:44 pm

Wow, thanks, guys. These are the comments I've been needing. Very much appreciated. I'm sure I'll have a few more questions but at the moment, I have one. I had occasion to replace the original solar controller with a Blue Sky Solar Boost 3000i. It has an Ah setting for the readout but it doesn't seem to function, unless I don't understand how it works. If it does function correctly, would that suffice as a battery monitor?

The amp-hour reading threw me for a loop also until I read this in the manual. At first I thought it was reading how many amp-hours the batteries were at:

SOLAR CHARGE AMP-HOUR COUNTER
The battery essentially serves as a “storage tank”, with the battery storing electrical energy in units referred to as amp-hours. Amp-hours are computed by multiplying current in amps X time in hours. For example 20 amp-hours may be a current of 10 amps flowing for 2 hours, or may be 1 amp flowing for 20 hours. The battery receives and stores amp-hours when being charged, and then delivers those stored amp-hours when being discharged. The amp-hour counter displays total solar charge amp-hours accumulated since the last time the counter was cleared up to a maximum count of 999 amp-hours. Amp-hour production varies widely with operating conditions, but as a very broad brush approximation 100 watts of PV modules can deliver up to a maximum of about 30 amp-hours per day. Any partial shading, lower sun intensity, shorter days, or time spent in Absorption or Float will decrease amp-hours produced. The present amp-hour count may be cleared by pressing Display Select for 5 seconds while viewing amp-hours on the display.

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