Goin’ Solar! DIY

[Bob K]

Originally Posted by jjason

Here is my progress so far:
Mounted 1500W pure sine wave inverter.

What method did you use to attach the inverter to the thin paneling? I think I see a board mounted to the paneling and L-brackets. Does the hardware go all the way through the paneling?

[lateott]

I think 2/0 is the right choice. I went with 2/0 based on my inverter’s instructions, and mine is only 2000W.

Also, I found it very easy to drill through the floor right outside the main frame rail after seeing the water tank overflow hose go right out there. Much easier than working my way through the enclosed underbelly. I used a pre-made cable with lugs attached, scraped the frame rail down to bare metal where I attached the lug.

(Photo should be rotated 90• clockwise)

[jjason]

Originally Posted by Bob K

What method did you use to attach the inverter to the thin paneling? I think I see a board mounted to the paneling and L-brackets. Does the hardware go all the way through the paneling?

There is a vertical slat (1x2?) under that cross piece that supports the bunk. I added a 2nd slat to the left. You can actually see my pen lines on where I added it. Then I attached some 1/2" scrap plywood/OSB to those.
There is nothing visible on the outside of the paneling. I attached my slat with a pocket hole kreg jig screw.

The L brackets came with the inverter.

[campin]

Originally Posted by lateott

I think 2/0 is the right choice. I went with 2/0 based on my inverter’s instructions, and mine is only 2000W.

Also, I found it very easy to drill through the floor right outside the main frame rail after seeing the water tank overflow hose go right out there. Much easier than working my way through the enclosed underbelly. I used a pre-made cable with lugs attached, scraped the frame rail down to bare metal where I attached the lug.

(Photo should be rotated 90• clockwise)

Clean looking install. Did you apply any treatment between metals to reduce oxidation/corrosion? If so what did you use (dielectric grease, Vaseline, etc.)? Thnx

[campin]

The way things are going, I’m boondocking in the winter and have an efficient Mr. Heater. But when sleeping my source of heat is a toasty 24V electric blanket.

[Mikec557]

Originally Posted by campin

The way things are going, I’m boondocking in the winter and have an efficient Mr. Heater. But when sleeping my source of heat is a toasty 24V electric blanket.

We use a king size electric mattress pad. Although it's low voltage like cold weather motorcycle gear, it plugs into 120vac. Just one more reason we have an inverter and lithium batteries. LOL.

[DanNJanice]

Originally Posted by campin

been AWOL but finally drafted a wire diagram. Thnx for reviewing and your thoughts, it’ll help me a lot!

Hi Campin,
I was examining your schematic and noticed you are using the LVD function of the battery monitor. Do you have any info regarding how much current the coil of the relay draws? Also, you show both NC and NO contacts on the relay, does that model have both contact sets? I ask because most automotive starter relays only have a NO contact.
Do you have a manf/model number?

[campin]

Originally Posted by DanNJanice

Hi Campin,
I was examining your schematic and noticed you are using the LVD function of the battery monitor. Do you have any info regarding how much current the coil of the relay draws? Also, you show both NC and NO contacts on the relay, does that model have both contact sets? I ask because most automotive starter relays only have a NO contact.
Do you have a manf/model number?

The control circuit of the NO SPST 24V 200A Continuous Duty Solenoid draws about 0.34A. Cole Hersee Part No.: 24214-BX. The relay symbol in the schematic is the only one offered by the software so ignore it : )

[campin]

As I wait for parts and tools, I equalized voltages between cells by connecting them in parallel. Readings were 3.299 to 3.302 volts...now all at 3.301 (70% SOC). I’ll bottom balance (for my application) the battery pack prior to installation.

[jjason]

I received my batteries. I connected them in series and charged them with my 12V 50 amp lithium charger.

I then connected them in parallel with a power supply set at 3.65V to top balance. I waited until current from the supply dropped to about 200mA.

Connected them back in series with BMS attached and charged with my charger.

Hooked up inverter and used a heat gun to put around 60AMP load from batteries until BMS triggered low cell cut off. Noticed BMS current measurement is over measuring by around 20%.

Connected external shunt to BMS to measure current.
Charged battery with my 50 amp charger until BMS kicked off cell over voltage.

Looks like usable energy in battery is around 3.87 kW-hr

I need to calibrate the current measurement on the BMS. This is possible using a Windows application, but requires a TTL->RS232/USB converter which I don't have on hand. Will do that soon.

After going through this exercise, I'm not sure how you can ensure you don't over charge or over-discharge a cell without a BMS monitoring those voltages.


Pictures:
1. top balancing
2. "assembled" battery
3. charging through BMS
4. external shunt measurement after charging.

[campin]

Originally Posted by jjason

...After going through this exercise, I'm not sure how you can ensure you don't over charge or over-discharge a cell without a BMS monitoring those voltages.

I don’t suggest others X the BMS but it’s unnecessary in my application.

My cells and battery are monitored by an active balancer, charge controller, inverter, volt checker, smart battery monitor with Bluetooth/shunt and relay disconnect. And LiFePO4 chemistry is “very stable” if balanced properly. A BMS can have issues which I don’t need in the boondocks Lol. I’m not into battery management but battery monitoring (once a month). My system will operate 10% to 90% SOC (state of charge) as recommended by the manufacturer to prolong battery life. All’s good and I’ll report performance

[campin]

And for those who’ve a sense of humor....

[jjason]

Well I am pretty much done.
I put battery in trailer.
Put dc-dc charger in trailer
Wired it all up
Removed old battery thats on the tongue and associated wiring
Ran new wire to break-away switch from new battery
Did some discharge and charge tests and pulled break-away switch to ensure it worked properly.
Replaced old smoke alarm
Installed new smoke alarm near battery

Some problems/notes I encountered:
1.My original choice of a 150amp breaker would trip on a 60amp load after a few minutes. It would trip on a 120amp load in a few seconds. Replaced with a different 200 amp model.
2. I misunderstood how the ac->dc converter worked. I was assuming I could just take some kind of output from the box and hook that up to my dc-dc charger input. Now I see the "output" is also an input in battery mode, its all tied to the same bus so my idea was not going to work. Fortunately I had an extra slot available in my transfer switch. Now, I redirect the DC line of the converter to either the input or output of my dc-dc charger based on transfer switch position.
3. Tested charging from my tow vehicle. To my surprise, I was getting 18 amps to the battery, after a few minutes it increased to 20 amps. Voltage at TV battery should have been 14.2-14.4V. Voltage at dc-dc input was around 10.4V. I measured 32amps on the input side of the dc-dc charger. All seemed good until I went to unplug the 7pin harness. It was pretty toasty on the trailer side, and it looked like some of the plastic may have been melting. All my wiring elsewhere felt good.
The charger has a setting to limit charge output to 10amps instead of 20... just needs an input driven high. So I wired up a 3 position switch that lets me change from "charge off" to "charge at 20amps" to "charge at 10amps". I'm just going to need to remember to do this when the 7pin is plugged in.... I should probably replace my current breaker on that line to a 20amp or something.
4. Everytime I turned on my inverter, the BMS would trigger some over current alarm and disable output (even with no load on output of inverter). Saw a setting that is some in-rush short circuit protection. Increased the limit from 111 amps to 200 amps. No problems thereafter.
5. Can run the microwave. Pulls ~120amps from battery. Ran for two minutes just to test. Haven't tried longer.
6. Did a full capacity test with just air conditioner running. Ran for 4 hours and 33 minutes. I was shooting for 4 hours so this is pretty good. It was a cooler day today, not sure if a hotter day will use more energy or not.

Still need to:
1. Secure battery
2. Tidy up romex wiring
3. Figure out a decent way to hook up my portable solar panels to charge that way. I thought about this after I removed all my old battery wiring on the tongue. Maybe I could have a mating connector at the 7pin harness and charge that way.
4. Find out where the handle to my transfer switch went....

[campin]

Originally Posted by jjason

Well I am pretty much done....

Wow you’ve been busy, nice!

That’s weird the 150 amp breaker tripped under spec. I’ll use a 200 amp ANL fuse, hope all’s good.
I removed the 700 watt microwave after learning of low efficiency (40-60%) and replaced it with an instant pot. What’s cool is extra cabinet space with minimum modification, just make doors. The pot fits in there and an existing receptacle.
Anyway I’ll begin to install solar hardware on Thursday. ...I like where you placed the battery.

[campin]

I chose to bottom balance LiFePO4 cells and will build a DC discharger (power resistors, switches and heatsink) to slowly achieve 2.5+ volts per cell.

[jjason]

Originally Posted by campin

Wow you’ve been busy, nice!

Have a trip planned for next weekend! Too excited to wait to finish until after the trip. I think we have our overnight pit stop at cracker barrel to test it out.

[jjason]

I wasn't happy with the thought of accidently leaving the 20amp charge mode enabled and melting my connector, so I added an Anderson connector rated for the current.

When I originally wired the 7pin harness on the tow vehicle, I used spade connectors to make the jump to the 7pin harness, so that was an easy swapout.

I let my vehicle idle for about 30 minutes while running 32 amps through the connector. Neither the 7pin or the anderson connector got warm. The spade connector did get a little warm, but nothing like the 7pin previously did.

However, I see my 40 amp circuit breaker that protects this aux line tripped.. makes sense since its rating de-rates at elevated temperatures. After a few minutes it started charging again. I think I am ok with this. Maybe driving down the highway will allow it to keep cool and prevent tripping with all that airflow.

[mass-hole]

This is a really cool setup. The Wife and I and our (now) two kids boondock 95% of the time. I probably would not need this stout of a setup as we don't go that long, a downsized version would be awesome.

Also, I've really wanted to move my batteries inside, but the whole ventilation thing is an issue. When we get down below freezing at night and are running the heater off battery, they get really weak. A lithium battery would be a great way to go but $$$.

[billcf7]

Lithium aren’t much more than AGM and keep getting cheaper

[mass-hole]

Originally Posted by billcf7

Lithium aren’t much more than AGM and keep getting cheaper

Looking around, it seems like Lithium is about 2x the cost of AGM for the same AH rating. You can get a 100 ah AGM for about $250 whereas it seems like the Lithium batteries are around $450-500? Am I missing something?