looking for charge controller for a 275 watt, 31v, rated current 8.9amps solar panel. I want to charge a 12v battery for my boat.

[billfloat]

I was given a 275 watt, 31v, rated current 8.9amps solar panel. I want to charge a 12v battery for my boat. I'm a complete novice at solar. Previously there was a smaller solar module connected to a charge controller that matched it. .I'm hoping to find a charge controller to charge a 12v 100ah battery that sits on the dock. There is a connection that lets me connect the 100ah battery in the boat to the other 100ah battery on the dock. That's all I want to do so I'm hoping it won't be too expensive. So I need a charge controller to fit the module but I'm not sure which one to get. Thanks!

 

[Dzl]

Victron Smartsolar 100 | 20 would be a good fit. 75 | 15 could work too but is slightly undersized.

 

[billfloat]

Victron Smartsolar 100 | 20 would be a good fit. 75 | 15 could work too but is slightly undersized.

So I need to get kind of a fancy one for this size solar panel?

 

[Dzl]

So I need to get kind of a fancy one for this size solar panel?

Not necessarily, it depends on your goals. Victron makes really solid products and the bluetooth app is very nice and simple and configurable, that's what draws me to them, and makes them my first recommendation.

But there are cheaper options if that is the priority. Epever is a popular value oriented controller. A PWM controller would be cheapest but it wouldn't be a good fit with your panel, maybe someone else can chime in?

 

[Bob142]

So I need to get kind of a fancy one for this size solar panel?

You will need an MPPT style solar charge controller (SCC) to take full advantage of that panel charging a 12V battery.

I don't recommend a PWM SCC. The combination of an old-school PWM, a 12V battery, and your panel's open circuit voltage (Voc) of 39.4V and rated current (Imp) of 8.94A would reduce your 275W panel into something like a 120-130W panel. The PWMs basically pull the panel voltage down to the battery voltage. So as an approximation just to show you an example, you'd get 8.94A x 13.5V = 120.7W.

I looked around to see if I could come up with an inexpensive, easy, and reliable MPPT option for you. You may be able to get away with the Victron BlueSolar 75/15 ($89 on Amazon) if your batteries are AGMs and can live with the default charge profile settings shown below (from the manual):

• Default absorption voltage: 14.4V
• Default float voltage: 13.8V

(I was told by a tech support manager at a Victron reseller that the BlueSolar line default charge profile is aimed at AGMs.)

If that charge profile works, you could use it right out of the box and not worry about paying extra for the SmartSolar with built-in Bluetooth. Down the road you could buy the Victron Bluetooth dongle if you needed to use the SCC on a different type of battery.

If you can't go that route, you are still in it for a min of around $80 for an MPPT SCC, even if you go with the budget Epevers.

 

[billfloat]

Appreciate the replies. I'm really a beginner in this area. Although the solar installation will stay on the dock it may only really be used for the next year. After that the boat may be sold and the dock left empty. It could be that another comes along later and really uses the solar but right now I'm looking for the cheapest way. During the heat of the summer the boat might get used once a week for a bit. There's also a motion sensor 12v light on the dock. When it cools off, sometimes the boat's trolling motor battery might be used each or every other day so it would be great if it could be replenished overnight. I didn't know about those agm batteries. They're pretty expensive. Originally I thought I would just get a 100 mah deep cycle lead acid battery for the dock battery box. Right now it has two extra large 6v lead acid batteries connected together but they seem to have run out of life as they quickly drop down to 11 volts after a charge (from a landline charger). Thanks for the help on this.

 

[Bob142]

Let's see if we can sort out how to keep it cheap given the short time this would be in use.

1. What was the wattage of the original solar panel?
2. Do you still have the charge controller from it or is the whole setup gone?

My thinking now is that if the other panel was 100W or smaller, you'd still be getting an upgrade in charging capability if you used the bigger panel and a PWM SCC. If you still have the original SCC we can check out the specs and see if it could be used with the bigger panel. If you don't have it, we can find a decent PWM for you that won't come anywhere near the prices of the MPPT SCCs.

 

[billfloat]

Interesting. Yes, It's still there. I'm going to go down and have a look at it. Thanks.

 

[billfloat]

It's a Thunderbolt
I found this for product 96728 at Harbor Freight:

Product Overview
This solar charge regulator protects and regulates the charge of a 12 volt storage battery using solar panels. The solar charge regulator features three LED indicators (high voltage, low voltage, charging) and three connections for the solar panel (keyed two-pin connector), battery (keyed two-pin connector) and 12V output (3 in. pigtail). The regulator provides overcharge protection at 14 volts and discharge protection at 10.5 volts.

• Prevents battery overcharge and discharge
• Three LED indicators (High Voltage, Low Voltage, Charging)
• Three connections for: Solar Panel (keyed two-pin connector), Battery (keyed two-pin connector), and 12V Output (3 in. pigtail)
• Overcharge protection at 14 volts
• Discharge protection at 10.5 volts
• Maximum input voltage: 22 volts

Important Information

• For use with 100 watts max solar panel input

 

[Bob142]

Maximum input voltage: 22 volts

That spec takes it out of consideration since your new panel will put out well over 30V. Then there's that blunt warning about if you exceed 7A you risk fire. So let's not risk fire!

I should have asked this in the beginning: what's the max you're willing to spend on a new charge controller?
Once I know that number I can do some thinking and digging (maybe others will help too) to see if I can come up with something suitable.

 

[DASH]

You may find this helpful.

 

[billfloat]

That spec takes it out of consideration since your new panel will put out well over 30V. Then there's that blunt warning about if you exceed 7A you risk fire. So let's not risk fire!

I should have asked this in the beginning: what's the max you're willing to spend on a new charge controller?
Once I know that number I can do some thinking and digging (maybe others will help too) to see if I can come up with something suitable.

Well, as I said, I don't have background in this but strictly in terms of what I hoped to spend I guess 50-60 would have been what I had thought about. It would be good to get a quicker charge from the bigger panel if possible but not critical. My friend brought it over. He only has experience in solar for his house going into the grid. He had a few extra of these so he could spare this one. He had no experience in what I'd be doing so he said he'd learn from me in case he might want to do something similar in the future.

 

[Bob142]

Good news, there's a seller on eBay listing an Epever Tracer2206AN 20A MPPT for $60 new. I don't have personal experience with them, but the Epevers are a popular budget MPPT (as @Dzl pointed out). I had only seen 20A Epevers for over $80 but those are the 100V models. I didn't realize Epever also made a 60V (46V at 25C) cheaper model. Since you only have a single panel with max open circuit voltage of 39.4V this controller is compatible and should work well for you. With it you'd be able to take advantage of all that extra power.

20A 10A Epever MPPT Solar Charge Controller 12V/24V Battery Regulator Max PV 60V | eBay

Battery Temperature Sensor Epever Monitor Adapter RS485/USB Communication Cable. when the internal temperature reach 81â, the power reduction mode will be turned on. MPPT 1000W Grid Tie Inverter For 18V/36cells Solar Panel AC110V SolarEpic Power.

www.ebay.com

 

[billfloat]

I went ahead and ordered it. Thanks a lot for the help with this. I guess now I need to order some cables with those special ends that to go between the panel and box. They'll be pretty close together.

 

[Dauntless]

Sorry I saw this so late.
I used a cheap, $25 PMW controller for the last 6 years on my boat for 200W of solar panels. Worked fine. While I just changed to an MPPT, it was for other reasons.

 

[billfloat]

I received the charge controller today. Looks fine in terms of shipping condition. Since my panel has those special connectors I was looking at some cables on Amazon with the connectors on one end and the bare cable on the other. I was looking at something like this. https://www.amazon.com/iGreely-MC4-...B07V3L4FQQ/ref=psdc_13638744011_t1_B07Q467BYY For my purposes do I need the thick cable like 10 or would less do the same? Fairly pricey for two cables but it's all ready to go. I'm assuming it's best to get the cable all in one piece rather than soldering yourself? I'm going to set it up by the house just to see that it's working before figuring out the dock setup. Thanks!

 

[Bob142]

I received the charge controller today. Looks fine in terms of shipping condition. Since my panel has those special connectors I was looking at some cables on Amazon with the connectors on one end and the bare cable on the other. For my purposes do I need the thick cable like 10 or would less do the same? I'm going to set it up by the house just to see that it's working before figuring out the dock setup. Thanks.

It depends on how many feet the panel will be from the charge controller when installed at the dock. You can use a voltage drop calculator to guide you. Shoot for 3% or less voltage drop. Here's a link to one where I punched in some numbers to show you how it works:

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

 

[billfloat]

Appreciate the link. I went ahead and ordered those 10 foot 10 thickness cable. I feel the odds are the panel won't be too far from the battery box. Next to get a battery and will be trying it out. Thanks

 

[Bob142]

Appreciate the link. I went ahead and ordered those 10 foot 10 thickness cable. I feel the odds are the panel won't be too far from the battery box. Next to get a battery and will be trying it out. Thanks

Cool. Keep us posted on your progress.

 

[Bob142]

@billfloat, how’s the little Epever working out for you?

 

[billfloat]

Hi. I think it's been working well. Really appreciate the guidance. Actually, I've waited to reply because I've been putting together some video clips and pictures showing how it is now to see how I should proceed. I've got a temporary setup just to see if the batteries are charging. They are. I've been experimenting with the solar panel on ground level but haven't been able to quite figure out how to mount it on the roof. Anyway it's going to take me a little more time to get that video done. Thanks!

 

[Bob142]

Hi. I think it's been working well. Really appreciate the guidance. Actually, I've waited to reply because I've been putting together some video clips and pictures showing how it is now to see how I should proceed. I've got a temporary setup just to see if the batteries are charging. They are. I've been experimenting with the solar panel on ground level but haven't been able to quite figure out how to mount it on the roof. Anyway it's going to take me a little more time to get that video done. Thanks!

Didn't mean to jump the gun! I look forward to your next official update. No pressure...

 

[billfloat]

It's currently set up on the gangplank. There used to be a smaller one mounted by the roof facing at an angle south. This panel is 2 -3 times bigger than the old one so I don't think that mount would be strong enough. I just positioned 3 different ways on the gangplank to see if it was working. I'm hoping it's much bigger than the minimum needed to charge 2 batteries (60ah and 100ah)? Right now I've got the older 60ah in the box and the new 100ah in the boat for the trolling motor. The plan is to put the 100ah in the box and replace the older 60ah. At night there a 12v motion sensor LED light that's pretty bright. It rarely comes on, as far as I know. Originally I had it connected to the "load" terminal on the box but it didn't seem to be working right. I then connected the light straight to the battery. I tried it the other night with the light going and it moved the 60ah battery immediately down to 12.3 volts but it was right up to 13.8 the next daytime. I'm thinking on the roof is the best for the future but now am unsure how to mount it. The roof slopes to the east at the entrance which would be the most convenient place. It's charging fine so I'm hoping it won't have to be in the perfect position as that might be a lot of work to do that on the roof? Occasionally, on the worst weather days, there can be pretty strong winds. Most days are pretty mild though. That other, smaller solar panel was able to handle the wind although at the end one corner showed a small crack.The area is kind of in a little valley on 3 sides. Thanks again for the advice. The box seems to be working fine! https://youtu.be/EoDR26fdopI

 

[billfloat]

So, basically, I now wonder if I should use the post from the old solar install, in some way, to tilt the panel a bit south or take the easier way and just put it in the direction of the roof line above the gangplank. It would be getting sun but tilting eastward.?