Lithium battery in Lil Snoozy - Fiberglass RV


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Old 05-22-2018, 09:38 AM   #1
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Lithium battery in Lil Snoozy

I have finished the LiFePO4 battery installation in our Lil Snoozy. We used the Li battery boondocking for 4 days a few weeks ago but I finally hard wired in all the pieces, including the ability to charge while driving, yesterday. I am no expert in batteries and chargers, I am a geologist. So I may have done something really stupid in my installation. I am only describing what I did. Please do your own research and make your own decisions. Please let me know if you have ideas for improvement.

Putting in a single Battle Born 100 Ah battery ended up not being a drop-in installation. It did eliminate the need for a battery management system, which made the installation much easier. If you mainly camp in RV parks and can plug in every night, you can just drop in the BB Li battery and be fine (but then you don't need a Li battery) but if you boondock, you need to make some changes. Only the charger wiring is absolutely necessary but you will significantly limit the benefits of Li batteries if you donít do the others. Why buy an expensive, high performance battery and then handicap it?

The changes I made are:

Replace the stock WFCO 9835 35 amp charger/converter with one that is designed for Li batteries. A Li charger will charge at higher voltage and higher amperage and doesnít have features designed just for lead acid. The WFCO won't charge the Li battery unless the voltage drops pretty low (see initial post in this thread). So this change is not entirely mandatory, but pretty close. One of the advantages of Li is high-amp charging so you can fully recharge in an hour or two off of shore or generator power instead of many hours for lead acid. I installed a Progressive Dynamics 60 amp lithium charger purchased from Battle Born. The Progressive Dynamics charger/converter charges at 14.6 volts, but the BB Li battery is regulated against overcharge at 14.4 volts, so no problem there. When I charged a 90% full battery with the new charger and wiring, it charged at 55 amps, as designed. Another advantage of the PD charger is that the fan doesn't come on all the time like the WFCO, and when it does, it is really quiet.

Replace the stock 12 gauge charger/converter wiring with 6 gauge so you can charge at up to 60 amps. This is a big deal. If you keep the WFCO 9835 and try to charge a depleted LiFePO4 battery with it, it will charge at close to 35 amps, which far exceeds the ampacity of the 12 gauge wiring supplied with the Snoozy. It is even worse with the Progressive Dynamics 60 amp charger I installed. So you must replace this wiring.

Build a new battery rack. You don't need the big, plastic battery box because the LiFePO4 battery is solid state and not lead acid. That frees up a ton of room and you can easily fit two BB Li batteries between the hot water heater and the hatch door.

Install a 300 amp fuse on the battery because it has the ability to discharge to a short at a much higher rate than the stock AMG battery.

I installed a Victron battery monitor (BMV 700) with dongle so I can keep track of charge level, amp-hours used, and charge/discharge rates. This is not essential but it is really hard to track battery status doing it manually with a multimeter. There is a video on the Battle Born website on how to program the monitor for their battery.

My 4Runner has a factory isolator that keeps the trailer from draining the vehicle starter battery in camp with the engine off. If you don't have that, you will have to install one, or unplug the trailer wiring harness in camp. This is a potential issue with either lead acid or Li batteries, but the next paragraph describes a much better solution to a battery isolator alone, that is needed for the Li battery.

To charge the Li battery while driving, you need to install an isolated DC/DC converter between the tow vehicle and the battery. I use a 7-pin tow connector so that the vehicle will charge the battery and run the Truck Fridge while driving. It is optimum to arrive at camp with a cold fridge and charged battery. The stock trailer AMG battery setup works okay because the vehicle and trailer batteries are both lead acid. But the Li battery has a higher voltage at full charge so it won't charge from the vehicle without a modification. While driving, a fully charged trailer Li battery will actually discharge to the vehicle lead acid battery. To prevent this and charge the trailer Li batteryn instead, the DC/DC converter takes alternator current at, say, 13 volts and bumps it up to 14 volts or so, enough higher to charge the Li battery. Putting the DC/DC converter near the trailer battery also takes care of the voltage drop from the alternator over ~30-40 feet of 12 gauge wire to the trailer battery, which is probably about 1 volt. I got a Victron DC/DC converter (Victron Orion-TR 12/12-9) and set it to charge at 14.2 volts, although it can be set to charge higher. Since it is isolated, it also prevents discharge from the trailer to the tow vehicle. When charging a 90% charged battery it was running at 8.5 amps, plenty for a fast recharge.
Finally, I installed a battery cut-off switch that I can use to isolate the battery for storage or in case of a short somewhere. This is something I would install regardless of battery type.

How has it worked? I didnít have the DC/DC converter installed when we went camping so we went more than a day without charging on the trip down. There was plenty of power to run the fridge, lights, and water pump for over a day. The stock AMG would have been nearly depleted. I used my generator for 30 minutes one day and I vampired off of my neighborís generator for 45 minutes another day. I got plenty of juice and returned home with about 70% charge remaining. We head out for a 5-day trip this weekend and I will report back afterwards.
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Old 05-22-2018, 08:31 PM   #2
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Sounds like an interesting set up. Please post some pictures when you are able to, I had to get over ten posts before it would let me. I will be redoing the electric system in my camper and would like lithium but the cost is a hard one for me to swallow. Two 6v batteries are so much cheaper and I am less concerned about weight. I would also be interested in your DC amp consumption vs what you are running. What is your truck fridge drawing in real life? Are you planning to draw your battery down to 80 or 90 percent?
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Old 05-22-2018, 11:23 PM   #3
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Doug, thanks for the informative write-up. When our AGMís die, the Battle Born batteries are what I will be getting, so it looks like I will also be adding a few other features that you mentioned.
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Old 05-23-2018, 04:16 AM   #4
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Doug, nice post.
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Old 05-23-2018, 07:39 AM   #5
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Thanks for the post. I am considering a BB Li battery for my LiL Hauley buildout. It sounds like you have considered all the design aspects. My estimation is that, due to the lower weight as compared to a lead acid battery, you took about 40 pounds off your tongue weight.
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Old 05-23-2018, 07:48 AM   #6
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Gene,

Thanks for the info on posting pictures. I tried to and wasn't able to, so I will post a few more comments first, then try again.

I don't keep a log of our real life power usage but do pay attention to it. The Truck Fridge draws from 3.5 to 4.5 amps when running. It doesn't run all the time and runs more when it is warmer out, of course. I budget for it to run 1/4 time.

One of the vampire loads was the illuminated power and light switches that came with the Snoozy. They draw about 0.1 amp each. So leaving the master 12V switch on for a day uses 2.4 amps. I swapped two of them out for LED-illuminated switches which use a few milliamps each.

I am planning to draw down to 20% although I don't have a big problem with going lower if I have to. Right now I am still hauling the generator so there is no need to go lower. On the other end, there is also no need to charge up to 14.4 volts. I set the DC/DC converter to 14.2 and plan to turn off the Progressive Dynamics charger when it is close to that as well.
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Old 05-23-2018, 07:54 AM   #7
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Carl,

I didn't weigh the two batteries so don't know for sure but your estimate of weight savings sounds about right. The battery sits just in front of the axle so I am not sure about how it affects the tongue weight. The Snoozy is so light that I don't worry about it and didn't notice a difference in practice.

Another aspect that I didn't appreciate until the installation was the space savings from doing away with the battery box. My initial plan was to build a rack to stack two BB batteries on their side, one on top of the other, next to the hot water heater. I even had all the aluminum supports cut. Then I realized that there is enough room to mount them on the floor. That was much simpler and more secure.
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Old 05-23-2018, 08:21 AM   #8
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Doug,


Weight distribution is a big consideration for me, since I am planning to move the water heater and pump under the sink, and install fresh water tank(s) beneath the trailer, like the grey water tank, and not have the sofa, so I can open up the 'living room' area. We are planning to have two swivel rocking deck chairs and a drop leaf table, where the sofa is.
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Old 05-23-2018, 09:27 AM   #9
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Doug,


I re-read your original post and have one concern regarding the 300 amp fuse. Because the battery can deliver high currents does not mean you should base your fuse size on it. The purpose of fuses, in most cases, is to protect the wiring from overheating and burning up. For example if you have 30 feet, to and back from a load, of 16 awg wire, the total resistance is 4 milliohms/foot times 30 feet or .12 ohms. 12 volts divided by .12 ohms is 100 amps. The fuse will not blow and the wire will dissipate 100 amps times 12 volts or 1200 watts. That spells fire! Make sure you have a heavy gauge wire from the battery fuse to the distribution panel. I would recommend a smaller fuse, maybe 30 amp time delay from the battery to the distribution panel and 10 awg wire or larger.


Regarding the charge circuit, you have to consider that the battery will also supply current if you have a short in that wiring. If you keep this wiring short (low risk of a short circuit) and of adequate size to handle the charge current you can probably not fuse it. If the wire is long enough to potential be shorted, I would put an additional fuse to the charger at the battery of sufficient size to handle the maximum charge current. Also make sure the wire is adequately sized.
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Old 05-23-2018, 11:34 AM   #10
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Nice job Doug. Can you give us the final cost to do this.
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Old 05-23-2018, 12:18 PM   #11
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The Renogy manual suggested a 40A fuse between my battery (100W Battle Born) and the 40A solar charge controller with 10AWG wire.
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Old 05-23-2018, 12:49 PM   #12
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Finally some sanity for Trailer Electrics

For at least two decades the numbnuts exploitative camper industry has been loading up campers with electrical amenities without concern for where the power comes from to run them to sell trailers off a showroom floor

This project is a breath of fresh air in that it recognizes the over provisioned state of consumer campers and the under provisioning of their power supplies.

None of the amenities is worth a hoot if they cannot be powered. It is time for buyers to hold manufacturer's feet to the fire and equip their offerings for real world use rather than owners having to remanufacture them.
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Old 05-23-2018, 06:12 PM   #13
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Rita,

The 40A fuse seems right for your solar circuit.

Doug
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Old 05-23-2018, 06:35 PM   #14
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Charlie,

Here is an approximate cost breakdown.

Doug

Battle Born battery - 950
Blue Sea 5191 fuse block - 19
300A fuse - 12
Cable, 6 gauge 2x10 feet - 54
Victron BMV 700 (minus bluetooth dongle) - 144
lugs - 8
Blue Sea 9001e battery selector switch - 35
Victron Orion-Tr 12/12-9A isolated DC/DC converter - 65
Misc. wire, shrink wrap, terminals, aluminum, screws, strap etc - 70

Total is about $1635
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