Battery Upgrade

[KemoSabeFLG]

Last summer I installed a basic solar panel array on my Imagine 17MKE. It consists of 3 each, Renogy 100W panels wired parallel through the pre-installed solar connector, and a Renogy Adventurer 30A PWN charge controller. This set up has served me well for boondocking so far.

Now it's time to get rid of the lead acid battery and upgrade to lithium. I will also upgrade my controller to a Victron MPPT unit. I am looking at getting 2 each LiTime 12V 100Ah batteries. The MPPT Sizing Calculator on the Victron web site recommends a 100/20 controller for my current 300W set up. If I calculate for adding 2 more panels, it recommends a 150/35 controller, and a 250/60 for three more panels.

My thinking is that I might want to eventually expand the system for 500 or 600W, and add an inverter. Should I get a controller that allows future expansion, or should I stick with one that fits the current set up?

Jeff Johnson
Yuma in the winter
Flagstaff in the summer
2021 Imagine 17MKE

[howson]

KemoSabeFLG -- easy question to answer. There's no downside (other than the cost) to getting a controller that can grow with future upgrades. Even if the upgrades are not done, the larger controller will still work fine.

You didn't ask for this info...but I suspect the Renogy panels are the same that I have on my 315RLTS. What you might not be aware of is that a Victron MPPT starts working at 5V above the battery voltage. The Renogy panel works at a Vmp of 17.7v. A typical lithium battery rests at 13.6V. With your three Renogy panels in parallel, can you see the problem? The Victron may never turn on as there must be at least 18.6V to start to start charging the battery.

What I did was tie two of the 100W panels in series (effectively making them 200W panels with a Vmp of 35.4V) and then I put six of these series-pairs in parallel (for a total of 1200W). This combination has served me well.

You can see what I'm saying in this chart from the VRM portal documenting the performance of my system today.



Howard

[TucsonJim]

Hi Jeff,

If it's within your budget, I'd go with a controller with the 150/35. It will work great for 2, 3, 4, or 5 of your Renogy panels. If you eventually go with more than five panels, you can control the other panels with a separate controller. The price difference between the two controllers is about $100.

If you're purchasing Victron equipment, I'd recommend you go with a dealer who will provide support before, during and after the sale. It may be difficult to get support if you buy from Amazon.

I used a company called NAZ, which used to be called Northern Arizona Wind and Sun. But there are many good ones out there.



Jim

[rtrainer]

There is a big jump in cost so you could by the smaller MPPT controller and just get another one later.

[KemoSabeFLG]

I appreciate the recommendation for NAZ. Since I will be spending most of the summer in Flagstaff, that's a good connection.

If I am interpreting Howson's advice correctly, I would need to rewire two of my three existing panels in series? Or, if I add two panels, wire those in series and leave the three existing ones in parallel? Or maybe just keep the existing PWM controller for now?

Thanks for the helpful replies!

[howson]

I appreciate the recommendation for NAZ. Since I will be spending most of the summer in Flagstaff, that's a good connection.

If I am interpreting Howson's advice correctly, I would need to rewire two of my three existing panels in series? Or, if I add two panels, wire those in series and leave the three existing ones in parallel? Or maybe just keep the existing PWM controller for now?

Thanks for the helpful replies!

An exhaustive explanation with full rationale is here: https://gdrvowners.com/forum/solar/1...n-2019-315rlts The first five posts in that thread speak specifically to your question.

Howard

[KemoSabeFLG]

My panels are Renogy RSP100D-BK-US. The specs show optimum operating voltage 20.4V, optimum operating current 4.91A. I didn't see a Vmp in the specs but I understand it's 70 to 80 percent of Voc.

Your discussion on the 2019 315RLTS was illuminating. Much more complicated than what I want to do but I learned a lot reading it. Thanks.

I'll be talking with the folks at NAZ next time I am in Flagstaff.

[Kathy&Jim_Imagine]

As usual, good feedback from the forum. And I apologize if I missed it in the conversation but my question(s) are; Why not size to what you currently have and if you decide to add additional panels down the road, simply add a second MPPT? Not knowing when "down the road" will be, you might not be able to get the same panels (or specifications) so there is a possibility of losing some of your charging capacity if connecting panels with different specifications together. And having a second MPPT doesn't hurt. If all your eggs are in one basket and the basket breaks... Just my thoughts....