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Old 03-12-2022, 04:38 AM   #1
Old_Salty
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Advice on Lithium and solar

We have a 2021 3791RD Legacy with the factory solar (not super solar) and FLA batteries. As our needs have changed, we plan on being off grid more and are looking to install 3 - 100 Ah lithium batteries to begin the upgrade process.

Our coach has an onboard generator we plan on using occasionally so we need the capacity to start the genny. 3791RD has the residential fridge.

The system has a Victron 100/30 MPPT. Stock converter and 2000 watt inverter. Stock shunt - how to connect genny leads?

Our concern is the ability to power the furnace and fridge through the night and the recharge time for the batteries. I am a newb in this and have found a lot of posts get quickly confusing as they tend to go deeper than I can comprehend at this point.

Thanks in advance.
 
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Old 03-12-2022, 07:42 AM   #2
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I would say you are just on the cusp of not having sufficient CCA to start your onboard generator under anything less than ideal conditions. I might suggest that you take a look at your design and consider keeping a small 12v AGM battery and trickle charger just for starting the generator. You could also simply increase your LiFePO4 bank size but only you know if the price delta is worth it to you. If your plans are to be off grid more and more just realize that one your 2000 watt inverter will not power all of your loads. The smaller inverter will actually complicate your wiring since it is incapable of powering one side of your power distribution panel. I suggest that you determine realistically how you want to live while off grid and then use that to guide your design. It may turn out that you will want to budget to change out some of your existing equipment. You may determine that you don’t need more than the 2000 watt existing inverter and you are willing to deal with moving inverter loads to a sub-panel. Bottom line is that doing this project twice is no fun either on you or your wallet.
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Old 03-12-2022, 10:46 AM   #3
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First, ID your converter so you know what you are working with. Lithium capable or not. Charge Wizard or not. Open the circuit breaker panel door, inside you will find a white sticker with the model number of the converter. Mine for example PD4575K18LS8.
It is not Lithium ready but it does have the charge wizard which I use occasionally in manual mode to boost up my Lithium batteries charge if I know I'm going boondocking the next day or so.
Go to PD website and download your manual.

Next, you need to do an energy audit. Figure out what each appliance draws and add it up. This will tell you how many amps per day you use. From this you can size your batteries and solar panels.
Excellent article on energy audit (in watt hours)
https://docs.google.com/document/d/1...t?usp=drivesdk

You can do the same thing in Amp/hours but you will need to distinguish (convert) between AC and DC.

For example, most batteries are rated in Amp hours. your furnace uses about 12A dc. Worst case scenario, on a cold night
12A x 12 hours = 144Amp hours (Ah).
If you have a 100Ah battery it will be long dead before morning.
On top of that you should NOT run a FLA battery below 50%. It will shorten its life.
Lithium batteries you can go down to 10% safely.

How to find happiness with lithium batteries
https://www.solacity.com/how-to-keep...tteries-happy/

Will Prowse on YouTube has excellent tutorials.
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Old 03-12-2022, 02:46 PM   #4
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I would check with battle borne batteries
battlebornbatteries.com
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Old 03-13-2022, 10:49 AM   #5
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Salty, I certainly understand how needs change and the implications. Lots of good suggestions already. If it were me, my first purchase would be a Victron battery monitor to begin developing an understanding of usage. I know if I look at my Victron app when I’m in bed with the lights out, I’m using 10 amps continuously. That 10 amps is device chargers, propane detector, night lights, satellite dish (draws power even when not watching TV), and the inverter when the furnace comes on, it jumps to 20 amp, unless the fan on the furnace is et to auto (this doesn’t work like I thought - it runs the fan on the heat pump along with furnace blower), in which case it jumps to 40 amps. Once you know your usage, then you can purchase what you need.

Based on personal experience (ymmv), it looks like if you take the wattage of solar and divide it in two, that is a good ratio of solar wattage to battery amperage. With our Super Solar (1200 watts/540 amps), we are able to recharge to 100% battery at the end of a typical day. Now, we’re running microwave, instant pot, TV, anything we have plugged in since the entire coach is live all of the time. We are typically down to about 50+% by morning. I find we overcome typical loads around 8:30 am and start discharging around 4:30 pm.

Here is where reality meets budget and wants/needs. Just add money. I know people that have 1000 amps of lithium and over 2000 watts of solar. I don’t have the budget or roof space for that on our 3230CK. Keep us posted on what you decide.
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Old 03-13-2022, 11:01 AM   #6
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Another thing to think about would be a small generator and/or a DC-DC charger.
I did a write up on my DC-DC charger install and results.
https://www.montanaowners.com/forums...hlight=charger
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Old 03-14-2022, 02:30 PM   #7
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Thanks for the info so far. It is appreciated!

After more research, the shunt is rated for 500 amps - so good there when starting the genny. The PD Converter - PD4575A - is one that is rated for lithium - has a switch to change to lithium. Next step is to start the genny and watch the load while cranking.

To clarify. we are not looking to go entirely off grid, I wasn't comfortable with the lead batts. Looking more for a day or two while traveling or at the races to help cut back on genny use.

Does the tow vehicle provide any amount of charge while driving? I have a stock 2021 Ford F450 with a 397 amp alternator. I know the 7 pin isn't rated for anywhere close to that - thinking maybe 10 - 15 amps. But combined with the solar panel (200 watt - OEM option from Keystone in 2021) it may help significantly on travel days.

Our genny is an Onan 5500 LP onboard. Again, looking to make our life a bit easier and more predictable to manage...
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Old 03-14-2022, 02:39 PM   #8
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On your 7 pin, figure around 5 amps +/- 2. Most people that want to charge batteries from their truck use either a Renogy or other DC-DC charger or a Smart BIM (Battery Isolation Manager). With my BIM I get around 40 amps per hour while driving. Of all the advantages of lithium (weight savings, elimination of voltage drop while discharging, ability to mount in enclosed spots, etc) the faster charge profile is a game changer. I can recharge 100 amps per hour.
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Old 03-14-2022, 02:45 PM   #9
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If you already have a PV array why are you bothering with DC to DC charging. Your array is charging whether you are driving down the road or not.
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Old 03-14-2022, 02:59 PM   #10
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Daryles - I should have read the post beforehand...
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Old 03-14-2022, 03:00 PM   #11
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There are those cloudy days.
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Old 03-14-2022, 03:03 PM   #12
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PNW Fireguy - We thought about keeping one of the lead batteries for starting the genny. We'll see what the actual load is for starting. Onan states 350 amps max. The online videos show it much less. I need to test at a lower temp.

Maybe my concerns are not well founded with a need to supplement the panel. As I stated, I am a newb and learning and maybe over thinking this.
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Old 03-14-2022, 08:46 PM   #13
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Depending on the lithium batteries you choose and how you many you install you can use your battery bank to start your Onan. We did this with our old rig and a 12v LiFePO4 pack. I believe that BB or Lion Energy even has a FAQ on the topic. I am not 100% certain but I believe their advice is that 3 of their 100AH batteries can work as a starting battery for the onboard generator but 4 would be better. Assuming my memory is at least somewhat accurate and the four battery configuration (min) is within your design needs and budget then this is a spot where you can both save a buck on installation and parts as well as simplify your installation by not requiring multiple charging profile capabilities. No dc to dc, no trick-L-charger, no battery isolator needed. I never measured the CCA but our old pack was set to autostart our Onan 6500 lp generator when the pack SOC was 10%(about 12.1vdc). It started everytime. I probably would not use a SOC that low if I were doing this with drop in ~100AH batteries because they generally have much lowere C ratings than the cells I used. 15% would probably be the lowest SOC I would attempt just in case.
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Old 03-14-2022, 09:08 PM   #14
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I agree there are cloudy days. But the OP has an onboard generator and either has or will have a PV array. I don't see any ROI for incurring the added costs of adding yet an additional charging source to the two existing...which by the way can only be used when hooked to the TV and it's running.
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Old 03-15-2022, 01:04 PM   #15
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I have 3 Renogy batteries on order - 100 Ah. Looking at the specs, 100 amp warning for discharge, 120 amp max trip. I'm hoping they will be adequate. We will know in a couple of weeks.

My rig has a 200 watt panel. With my current Victron 100/30 MPPT I should be able to connect another in series.

I guess I should have shared my thoughts from the beginning - utilize the batteries for their capacity, take advantage of the sunlight and top off with the genny as needed. The batteries were my biggest concern as I have the residential fridge, and wanted the capacity to run the furnace through the night and have enough reserve to start the genny after quiet hours were over to recharge. My convertor is lithium compatible and rated at 75 amps so I should have a decent charging rate available.

Not perfect by any means, but it will get us started and we will adjust, add-on, etc. as we go.

Again, I can't say this enough, thanks for the advice and suggestions!
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Old 03-15-2022, 04:00 PM   #16
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Old_Salty is your 2000 watt inverter a charger or inverter only? I am assuming that you have done your homework in selecting your battery choice. I would look hard at getting 4 if your budget will support it. If you decide to add batteries later try to do it before you get past 200-250 cycles. That's complete charge cycles. Your pack is only as strong as your weakest prismatic cell within those plastic cases. Best of luck with your plans. Don't forget to show your finished product.
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Old 03-18-2022, 02:24 AM   #17
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The invertor is inverter only. The converter is the charger - two separate devices.

After having some nicer weather and being able to open things up, I tested the starting amps for the genny. It was about 90 amps, much lower than I anticipated, given Onan's specs. The Renogy batteries (3) I ordered are 100 amp each max discharge so I am more comfortable with that.

The solar panel is actually a 300 watt panel, not 200 as I thought. If I add another panel, I would look to purchase one with similar specs and connect in series. The wiring in place would support that capacity.

I have learned a lot about this!
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Old 03-18-2022, 03:43 PM   #18
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Now you have extra budget to add more panels and upgrade your MPPT controller.
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Old 03-20-2022, 02:36 PM   #19
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Seriously consider building your own lithium battery. Search for will Prowse on you tube for all the info you need For $800 you will be able to build a 600ah battery compare to the cost of one battle born 100ah battery. Quite a bargain and very very easy to build!
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Old 03-20-2022, 04:08 PM   #20
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I have been living in my 2020 3719RD SuperSolar for 18 months. I find I used about 25% of my storage overnight. That's about 150 Amp hrs. Watch tv in the evening about 3 hrs then bed. Meter says 75% first thing in the a.m. winter time meter says 60%. We have 6 100Ahr lithium. Works great for us. 2000 watts solar and no generator.
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