Help me choose a new, compatible charge controller

Hi there! I just bought a used yurt with a used solar system. The charge controller is not reading properly (the screen turns off randomly and does not give reliable information) and I think needs to be replaced. I will also need to replace the batteries before winter. I'd like the new charge controller and batteries to be compatible with the existing gear. Can you help me figure out what to buy?

Currently I have:
3 LG 335 watt 24 V panels (only 1 is connected, will be in parallel due to shading)
Trace engineering C40 charge controller
4 6V Trojan T-105 batteries wired in series for 24V
Cotek SP-1000 inverter
Cotek CX2415 battery charger

I greatly appreciate your recommendations! I'm worried about getting something that is not compatible.

Evan

A Victron will be compatible.

YurtSolar said:

Hi there! I just bought a used yurt with a used solar system. The charge controller is not reading properly (the screen turns off randomly and does not give reliable information) and I think needs to be replaced. I will also need to replace the batteries before winter. I'd like the new charge controller and batteries to be compatible with the existing gear. Can you help me figure out what to buy?

Currently I have:
3 LG 335 watt 24 V panels

YurtSolar said:

(only 1 is connected, will be in parallel due to shading)

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Trace engineering C40 charge controller
4 6V Trojan T-105 batteries wired in series for 24V
Cotek SP-1000 inverter
Cotek CX2415 battery charger

I greatly appreciate your recommendations! I'm worried about getting something that is not compatible.

Evan

Click to expand...

First lets look at the specs to determine what you need.

With the 3 panels in parallel, the Array Voc will be the same as the Panel VOC: 41V. I don't know what temps you might experience so I will assume a really bad worst case of -41deg C. (-41.8deg F). The beta of the panel (Voc Temp Coefficient) is -.27 so the worst-case Voc is 48.3V. This says you should look for a controller that can handle at least 50V.

The total power from the panels will be 3 times a single panel: 3 x 335W = 1005V. Since it is a 24V system the current to the battery will be 1005/24=41.9A. This says you should look for a controller that can handle at least 42A of battery current. (assuming you go with a single controller).

For stand-alone controllers, I really like Victron SmartSolar. The SmartSolar 100 | 50 would be a good match.

YurtSolar said:

(only 1 is connected, will be in parallel due to shading)

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With shading problems, you might want to consider a separate controller for each panel. This is expensive but will get the most power out of the panels. Each controller would still need to handle 50V, but would only need to generate ~14A of battery current. If you go this rout, a SmartSolar 75 | 15 would be a good match.

BTW: You may want to think about any panel upgrades you might want to do in the future and buy larger controller(s) that can handle the upgrades.

Thank you @ncsolarelectric and @FilterGuy for this helpful information - two votes for Victron! Good to know they are compatible with my system. Very good reviews too! I've read a few that mention firmware updates - would I need an internet connection to use this charger long term? I don't currently have internet at home and not sure if I could do the required updates without it.

My electricity needs are pretty basic, I can probably use only one panel but all three were part of the package I purchased so I might as well use them. It looks like the smart solar 100|50 is $325 and the 75|15 is $90, so it would be cheaper to do one of the 75|15 chargers per panel (3 total), unless I have to account 3 6 AWG cable costs. Would I need to run 3 cables of 6AWG, one from each panel to each of the chargers inside the yurt? I could see the cost of the 3 cheaper chargers go way higher than the one larger charger if I need to run that much cable.

I am surprised that I need such a expensive charger, the previous owner used the C40 40 amp without issues although she also didn't put fuses on the 3 panels so maybe not the best example for my upgraded system

Thank you both!
Evan

YurtSolar said:

My electricity needs are pretty basic, I can probably use only one panel but all three were part of the package I purchased so I might as well use them. It looks like the smart solar 100|50 is $325 and the 75|15 is $90, so it would be cheaper to do one of the 75|15 chargers per panel (3 total), unless I have to account 3 6 AWG cable costs. Would I need to run 3 cables of 6AWG, one from each panel to each of the chargers inside the yurt? I could see the cost of the 3 cheaper chargers go way higher than the one larger charger if I need to run that much cable.

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How far away from the chargers will the panels be? Unless they are really far away, I would be surprised if 6AWG would be needed.

Check out this resource for fusing and wire size information.

YurtSolar said:

I've read a few that mention firmware updates - would I need an internet connection to use this charger long term?

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If everything is working then don't bother updating any firmware. This is best accomplished by never upgrading your copy of VictronConnect on your computer and/or smart phone once your system is up and stable. Your stuff will continue to run just fine.

The only reason to bother updating the firmware on a working system is because it provides some new feature you want or resolves some minor issue that you have been having. If you do need to upgrade then you can install the updated Victron Connect on your computer or smart phone somewhere that you have Internet access. Then bring that computer or smart phone to where your Victron gear is located. VictronConnect will then let you update the firmware without any Internet connection.

So, in short, you do not need an Internet connection for your Victron gear to run just fine for a long time.

YurtSolar said:

Would I need to run 3 cables of 6AWG, one from each panel to each of the chargers inside the yurt?

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You can use the existing pair of 6AWG if you put the 3 panels on one controller. If you put one panel per controller (3 controllers) then you can probably get by with 3 pairs of 10AWG wire between the panels and the controllers.

FilterGuy said:

How far away from the chargers will the panels be?

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You may wish to see the OP's other thread with lots of details.

YurtSolar said:

I've read a few that mention firmware updates - would I need an internet connection to use this charger long term?

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I agree with @rmaddy that once things are working you can leave it alone and not update the FW.

However, with Victron, you may need to hook up to the internet the first time you try to connect to the controllers.
On multiple occasions, the application insisted on upgrading the application when I tried to connect to the controllers. However, I was connected to the internet and the application clearly called home and found out there was a newer version. If you are not connected to the internet, this would not happen, but I don't know if there is ever a time when the application looks at the Firmware Rev and insists on an update to the Firmware.

Once you do get the FW and App synced, it should continue to work as long as you are not connected to the internet.

If you do need to sync things up on first connect, then you will need to take the controller to a place that does have internet and power it up.
The controller needs very little power so hooking a small 24V battery or even a small power supply to the controller should work fine. (You will not have to hook up solar panels to get the FW and Application synced up

FilterGuy said:

How far away from the chargers will the panels be? Unless they are really far away, I would be surprised if 6AWG would be needed.

Check out this resource for fusing and wire size information.

Fusing & Wire Sizing guidelines for solar panels

To get the paper, click on the orange'' button at the top of the screen. This resource is intended to help the user understand when they need to add Over Current Protection Devices (OCPDs - Fuses or Breakers) to the solar panel array and what...

diysolarforum.com

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Your other thread mentions 30Ft. Let's run some numbers on 30ft and 50ft for hooking the panels to separate controllers.

The key numbers for calculating voltage drop will be the Operating MP values.

• Vmp: 34.1 Volts
• Imp: 9.83 Amps

I will assume we are targeting a 3% or less voltage drop.
I like using this On-line voltage calculator.

Plugging the numbers in I find that for a single panel 12AWG would work for 30ft and 10AWG would work for 50ft.

@FilterGuy and @rmaddy this is incredibly helpful, thank you! I'm learning a ton from you both. Good to know I won't need Internet, or at least I can bring it to the neighbors house to set up at first.

It sounds like I have two solid options:

1. Order the Victron Smartsolar 100 | 50 and use my existing 30' 6 AWG to hook up all 3 panels in parallel. I like the simplicity of having only one charger, fewer cable connections outside and to the batteries, and less space used in the yurt. However I would need to add fuses to each panel as well. Total cost is ~$350 plus cost of fuses and maybe combiner box.

2. Order 3 Victron smartsolar 75 | 15 ($120 each) and ~150 feet of 10/2 UF-B cable ($220). This would be more efficient, let me place the panels further (up to 50' instead of 30'), and take away need for fuses, but take up more space in the yurt. Total cost ~$580. But I could start with only going up 2 of the panels which would cost $380 for 2 chargers and 100' cable.

I've contacted two local solar companies to see if they can order the Victron chargers. If not, I can order this week from Amazon. My C40 screen and LED indicator light is no longer working, if I bump it at all the screen turns off and it's giving inaccurate readings so the new controller will be a huge upgrade.

Which makes more sense to you? Keep in mind I'll likely upgrade the batteries, possibly to a single 24v LFP battery, and my electricity needs are limited (LED light, mini fridge, phones and laptop). I've tried charging the current batteries but they quickly drop from 28.9 V to 24.8 V so I think they might be dead.

Thank you SO much for working this out with me!
Evan

YurtSolar said:

$350 plus cost of fuses and maybe combiner box

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I have an Eco Worthy combiner box. (4 string $120) Not top shelf but it's been running 2 years without a problem.
https://www.eco-worthy.com/products...circuit-breakers-for-on-off-grid-solar-system
also sold on Amazon
They come in 4 or 6 string inputs, each string input is fused, there's a lightning arrestor and an output breaker.
Just for the convenience of having it all in a waterproof box is worth the investment, besides you'll spend about the same buying all the separate components of in-line fuse holders, fuses, breaker box and breaker and whatnot then having to put it together yourself.

Check CurrentConnected for the Victron Smart 100/50
https://www.currentconnected.com/product/ve-ssmppt-ved/
$324
A bonus is they can answer any questions you may have and I know from experience they will go out of their way to help.

wiseacre said:

I have an Eco Worthy combiner box. (4 string $120) Not top shelf but it's been running 2 years without a problem.
https://www.eco-worthy.com/products...circuit-breakers-for-on-off-grid-solar-system
also sold on Amazon
They come in 4 or 6 string inputs, each string input is fused, there's a lightning arrestor and an output breaker.
Just for the convenience of having it all in a waterproof box is worth the investment, besides you'll spend about the same buying all the separate components of in-line fuse holders, fuses, breaker box and breaker and whatnot then having to put it together yourself.

Check CurrentConnected for the Victron Smart 100/50
https://www.currentconnected.com/product/ve-ssmppt-ved/
$324
A bonus is they can answer any questions you may have and I know from experience they will go out of their way to help.

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Thank You so much for adding your experience here @wiseacre ! The combiner box looks good, although might be slightly less amps than I need? @FilterGuy said above I need to look at 42amp or above for the controller and I think the combiner box is limited to 40 amp, but maybe it's close enough? If so it looks like a great, convenient solution.

Current connected sounds like a gem and I'd be thrilled to order the Victron from them, thank you for the recommendation!! I'm not sure yet if I should move forward with 1 100|50 controller or 2-3 75|15, one for each panel - do you have a recommendation? Maybe I'll call current connected to get their advice tomorrow morning.

rmaddy said:

If everything is working then don't bother updating any firmware. This is best accomplished by never upgrading your copy of VictronConnect on your computer and/or smart phone once your system is up and stable. Your stuff will continue to run just fine.

The only reason to bother updating the firmware on a working system is because it provides some new feature you want or resolves some minor issue that you have been having. If you do need to upgrade then you can install the updated Victron Connect on your computer or smart phone somewhere that you have Internet access. Then bring that computer or smart phone to where your Victron gear is located. VictronConnect will then let you update the firmware without any Internet connection.

So, in short, you do not need an Internet connection for your Victron gear to run just fine for a long time.


You can use the existing pair of 6AWG if you put the 3 panels on one controller. If you put one panel per controller (3 controllers) then you can probably get by with 3 pairs of 10AWG wire between the panels and the controllers.

Click to expand...

@rmaddy and @FilterGuy I'm hoping to order the controller(s) tomorrow and would love your last take on which way to go, one 100|50 controller or 2/3 75 | 15 for 2 or 3 panels. What would you do?

YurtSolar said:

What would you do?

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That is really hard to say without seeing the situation. If the panels are all at different angles.... go with multiple controllers. If you can get the panels on the same angle and minimize the shading issue... keep it simple and go with one controller.

FilterGuy said:

That is really hard to say without seeing the situation. If the panels are all at different angles.... go with multiple controllers. If you can get the panels on the same angle and minimize the shading issue... keep it simple and go with one controller.

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I can definitely appreciate that, thank you for sticking with me as I figure it all out

Right now the panels are each on their own temporary stand until I get the system figured out, so I can still move them around. Seems like I'll probably be ok either way but it's hard to make the decision hahaha

The safest solution is separate controllers. No matter what, that will get the most from the panels.

FilterGuy said:

The safest solution is separate controllers. No matter what, that will get the most from the panels.

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Safer in terms of getting more energy to the batteries and having more energy to rely on or safer in terms of less risk of harm to people and equipment?

Also, am I right that with multiple controllers each connected to one solar panel I wouldn't need fuses or a combiner box? I read the pdf link you shared earlier and it says on page 4 you don't need a fuse for a single panel, and if I don't need fuses or a combiner box that could make up the cost difference between a single and separate controllers. That PDF also taught me that a disconnect should be between the panels and the SCC - currently it is been the SCC and the batteries, so I think I'll change that. Thanks for educating me!

3 controllers
no fuses, no combiner box
with only 3 independent panels I'd consider throwing a blanket over one to disconnect it safely instead of 3 separate disconnects

YurtSolar said:

Safer in terms of getting more energy to the batteries and having more energy to rely on or safer in terms of less risk of harm to people and equipment?

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Safer in the terms of getting the most out of them.

YurtSolar said:

Also, am I right that with multiple controllers each connected to one solar panel I wouldn't need fuses or a combiner box?

Click to expand...

Correct. No combiner box.

YurtSolar said:

That PDF also taught me that a disconnect should be between the panels and the SCC - currently it is been the SCC and the batteries, so I think I'll change that.

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Yes. The NEC code calls for a disconnect between the panels and the controller. However, unless you are trying to get code compliance for the yurt, I would consider it optional. The NEC code makes a lot more sense when you are dealing with strings of panels producing hundreds of volts.