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Old 05-02-2022, 02:48 PM   #1
sunshine 1
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Lithium. Batteries

I have 6 100Ah Battle born batteries connected in parallel. I would like to get 2 more with a total of 800 Ah battery bank. I am not sure if it is a good idea to have 8 batteries connected in parallel in case one goes bad. Will that affect the others?
Any input would be great.
 
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Old 05-02-2022, 03:28 PM   #2
PNW Fireguy
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As long as you don't have thousands of cycles on the existing batteries go ahead and add the two additional BB's. They are self contained batteries so if something goes wrong with one or more the internal BMS is designed to disconnect the battery from the electrical circuit.
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Old 05-02-2022, 04:33 PM   #3
rames14
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How many watts of solar do you have?
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Old 05-03-2022, 07:35 AM   #4
sunshine 1
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Thanks PNW Fireguy,
I have about 2000 watts of solar.
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Old 05-03-2022, 07:42 AM   #5
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The reason I asked about your solar is that about 2 x your battery amperage is a good rule of thumb for sizing batteries to panel wattage. If your battery bank is oversized for your panels, they will never get fully charged unless you are topping them off daily some other way. You are fine with 2000 watts for 800 ah of battery. If you had the space and $’s, your solar array could actually handle 4 more batteries.
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Old 05-03-2022, 08:03 PM   #6
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Since we are on the topic of solar charging a large battery array, what kind of charging efficiency are you folks seeing from your panels? Let's assume a fixed mount system and non-pivoting mounts. Summer months when the sun is overhead. I have just under 1200W of panels. Most of the time (like this time of year), I see 750-850W during mid-day. That's around 66-70%. I run my array in a series/parallel configuration. six panels total, (3 in series and paralleled to controller). It usually puts out 75-80V and 10-15A.

I'm wondering if I'm losing too much from using the tiny factory solar wires even though I'm well under 20A.

I'm contemplating adding a second controller and running heavier wire to the roof and splitting the two sides.
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Old 05-04-2022, 07:53 AM   #7
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I can tell you all of my panels are in Series. That prevents shade on one impacting the others. In January, our 1200 watts were producing about 4.2 kWh per day. We were seeing a charge from about 8-4 pm. So, about 525 watts per hour. As the sun gets more overhead, I would expect to see what you are seeing.

Here is a good Battleborn article. They figure 350 watts/day from a 100 watt panel.
https://battlebornbatteries.com/rv-solar-panels-guide/
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Old 05-04-2022, 08:07 AM   #8
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Lot’s to digest here however your PV output based upon the time of year and your stated parameters is not way off mean numbers. If your roof is curved and you have both parallel strings on the same SCC this could effect the MPPT for the SCC assuming that you are using an MPPT vs PWM SCC. Separating the strings to individual SCC’s will help maximize each strings output. Based again on what info you provided it sounds like you may be using 190watt panels that have an IMP around 9 amps. If that is the case the amperage output from your array is inline. The factory solar wiring at your PV array voltage would be a challenge for me. You can check the voltage output of your array on the roof and then check the voltage at the SCC input to get a idea of your voltage drop. The voltage not the current should be your concern for that wire run. Think of it as the pressure available to push the 14-15A of current from the PV array to the SCC. I have factory installed 10AWG wiring from my roof to the basement but my PV array runs at 150vdc. Any voltage drop is neglible. One more item if your panels have bypass diodes then shading degradation is minimized. Most modern panels have them but you can easily verify by opening the connection box on the back of panel or via the manufacturer spec sheet.

Added some historical data for reference.
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Old 05-04-2022, 08:39 AM   #9
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2000 w of solar and eight batteries, you could probably run an arc welder with that setup. ;-)
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Old 05-04-2022, 02:09 PM   #10
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Originally Posted by PNW Fireguy View Post
The voltage not the current should be your concern for that wire run. Think of it as the pressure available to push the 14-15A of current from the PV array to the SCC. I have factory installed 10AWG wiring from my roof to the basement but my PV array runs at 150vdc. Any voltage drop is neglible.

I have the Victron 150/85 SCC. I have four 160W panels and two 270W panels. They have the same operating current of 8.77A. I did try to run all six in series, but it over voltaged my controller during that experiment. I do want to run a couple more panels so I think I'll get another controller and split the sides of the roof for each controller. That'll keep me under 150V on each string and the shading from the ACs won't have such a large impact on production during the lower sun angles.
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Old 05-04-2022, 03:54 PM   #11
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Be sure to take into account temp correction when determining how many panels to put in series. My PV strings total just under 150V without temp correction however dependent upon how cold the weather turns where I am they could potentially put out 187Vdc which would have damaged a 150/100. Over paneling also seems to be the IN thing right now as well. Your controller is plenty big enough for the current. As you stated it's the panel configuration and the resultant array voltage that's limiting. I have the same issue. I have a pair of 250/100 in a 24v system. As per my previous post you will want to make sure that your panels have bypass diodes. They block the shaded panel while keeping the unaffected panel in series output functioning.
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Old 05-04-2022, 04:12 PM   #12
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Yep. When I ran that series test, the temps were in the 50's so the panels were kicking out more than the standard published values. I have the diodes.


This is the highest I ever saw for output to the batteries - 68A. It was midday in March last year.
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Old 05-08-2022, 02:41 PM   #13
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Quote:
Originally Posted by rames14 View Post
I can tell you all of my panels are in Series. That prevents shade on one impacting the others. In January, our 1200 watts were producing about 4.2 kWh per day. We were seeing a charge from about 8-4 pm. So, about 525 watts per hour. As the sun gets more overhead, I would expect to see what you are seeing.

Here is a good Battleborn article. They figure 350 watts/day from a 100 watt panel.
https://battlebornbatteries.com/rv-solar-panels-guide/
I think you mean in parallel, series connections are affected by shade but not like the old days but they drive an MPPT better.
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Old 05-08-2022, 03:00 PM   #14
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You are correct, Parallel. Senior moment.
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Old 05-08-2022, 06:28 PM   #15
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I think you mean in parallel, series connections are affected by shade but not like the old days but they drive an MPPT better.



Yup, bypass diodes make all the difference in the world.
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Old 05-08-2022, 09:42 PM   #16
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For your batteries to charge and discharge equally, be sure the positive and ground cables connect at opposite ends of the 8 battery string.
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Old 05-09-2022, 08:29 AM   #17
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Sorry, this question is not directly related to the thread, but I've been wondering how people can have so much solar - panels, batteries, inverters, etc. - without exceeding the GVWR of the trailer? We only have 2 x AGM batteries - no solar - and we are at/over the GVWR. I would love to have a similar setup described here - 8x Battleborn - 2000+ solar - but I can't afford the weight. Do you just pack light or have you done axle and suspension upgrades?
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Old 05-09-2022, 08:58 AM   #18
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I am not sure what all you are carrying in your unit, and since you didn’t mention year or model, it is difficult to give a full answer. Typically, lithium batteries are about 1/3 the weight of your AGM batteries. A typical solar panel will check in at about 35-40 lbs. Ancillary equipment like SCC’s and Inverters will add another 40 lbs or so. I am probably lighter than my 4 6 volt golf cart batteries in the last rig. We did upgrade our suspension to IS, but matching the 7000 lb axles that came on our unit.
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Old 05-09-2022, 09:56 AM   #19
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We have a 2017 Montana 3811MS with a GVWR around 16,800. We are definitely packing too much and too heavy. The last time I weighed it, we were just over 17K loaded. We were on the road for 4+ months last summer and 5+ the summer before. So, we had portable generators, tools and lots of "just in case" type of items. I'll have to do a better job of packing lighter - and try to convince my wife to do the same.
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