MPPT Battery Connection on Dual Batteries?

[Scrimma]

Hi everyone. I have a Dehler 39 monohull. I am installing 2x Sunpower E20 - 327W solar panels in parallel through a Victron SmartSolar 100/50 MPPT. The panels will be on an arch at the aft. Cables will be run into the STBD aft cabin to beside the engine near where the house batteries are located. That's where I would like to install the MPPT and then run charging cables to the house batteries which consist of 2x 260ah Fullriver sealed AGM (520ah house total).

My question is; would it be advisable to run the output cables from the MPPT to the one battery on the STBD side, or should I run positive to the STBD battery and the negative to the PORT side or vise versa? I want to make sure both batteries are equally charged. Both batteries are connected in parallel with very heavy duty cables, so voltage drop would be minimal, but I have heard can add up in the long run. The PORT battery is the one connected to the house loads with the STBD battery being the 'sleeper' in parallel.

Let me know your thoughts on that please

I also have a question about the size of cable I should be using for those panels to the MPPT (approx 25' run to the MPPT).

Additionally, what size cabling (maybe the same?) from the MPPT to the batteries? (3-6' away depending on battery I connect to)

Ive attached the spec sheet for the solar panels I will be installing.

Thank you all in advance for dispelling your wisdom!

Cheers

[ozsailer]

Hi Scimma,
I am a bit confused. I understand you have two house batteries being 2 x 260 totalling 520 AH capacity. You indicate that they are on either side of the vessel and connect in paralel by large cables. When you say one is the "sleeper" battery what are you actually referring to. Is it the case that you have an isolation switch so can switch from one battery to the other.
The other question I have is do you have a battery moniotor system with a current shunt as this may determine how you connect your system.


Greg H
Lagoon 440

[Scrimma]

Originally Posted by ozsailer

Hi Scimma,
I am a bit confused. I understand you have two house batteries being 2 x 260 totalling 520 AH capacity. You indicate that they are on either side of the vessel and connect in paralel by large cables. When you say one is the "sleeper" battery what are you actually referring to. Is it the case that you have an isolation switch so can switch from one battery to the other.
The other question I have is do you have a battery moniotor system with a current shunt as this may determine how you connect your system.


Greg H
Lagoon 440

Hi Garry. I can see the confusion caused there. I just mean that there is nothing coming off that battery directly as it ties into the PORT battery in parallel. There is no isolation switch.

I have recently installed a Victron BMV712 for monitoring batteries through the victron supplied shunt..

[Scrimma]

Originally Posted by ozsailer

Hi Scimma,
I am a bit confused. I understand you have two house batteries being 2 x 260 totalling 520 AH capacity. You indicate that they are on either side of the vessel and connect in paralel by large cables. When you say one is the "sleeper" battery what are you actually referring to. Is it the case that you have an isolation switch so can switch from one battery to the other.
The other question I have is do you have a battery moniotor system with a current shunt as this may determine how you connect your system.


Greg H
Lagoon 440

I just quickly sketched the current setup. Hope it's clear enough?

[ozsailer]

Thanks for the info. Based on what you have supplied I would connect the active supply from the MPPT to the positive terminal of the nearest battery. The shunt for my battery monitor is connected in series with the negative of our battery system and this is where I connected the neutral from the MPPT so I could monitor the power input of the solar panels. Ensure you connect to the correct side of the shunt if you do this.


Greg H

[Scrimma]

Originally Posted by ozsailer

Thanks for the info. Based on what you have supplied I would connect the active supply from the MPPT to the positive terminal of the nearest battery. The shunt for my battery monitor is connected in series with the negative of our battery system and this is where I connected the neutral from the MPPT so I could monitor the power input of the solar panels. Ensure you connect to the correct side of the shunt if you do this.


Greg H

Beautiful! Thanks for taking the time to help out Greg! Apologies for calling you Garry in previous post!

I'll definitely put the negative on the load side of the shunt. Electrical is definitely not my strong point, but man it's satisfying when plans start coming together.

One last quiz for you. I'm connecting a 1000w max continous pure sine wave inverter to the positive on the STBD battery and also running the negative to the load side of the Victron shunt. All should be good with that too right? It is just a regular inverter from repco. Not an inverter charger and the 240v side won't connected to the AC panel or anything. It will be a simple plug in type to allow charging power tools etc and running the odd kitchen appliance. I have a little generator for anything requiring more power for short bursts etc. Thoughts?

Link to inverter:

https://www.repco.com.au/en/brands/r...0-1/p/A9622428

Cheers!

[ozsailer]

Hi Scrimma, while I have an electrical background I am always reluctant to advise people, even in person without seeing what required work is to be undertaken with much of this type of work outside of my qualifications. In saying that I am happy to advise on some aspects of your work.
A couple of things I would raise. 1) Personally I would much prefer your batteries to be next to each other reducing or eliminating having batteries in different locations and othe associated issues such as voltage drop etc 2) I would highly recomend an isoation switch between the solar panels and the MPPT unit to make working on either much easier and safer. 3) You DO require a fuse or circuit breaker between the MPPT unit and your batteries. 4) Ensure you read the manufacturers installation manual on the correct procedure for connecting your solar panels and batteries to your MPPT unit. 5) Also ensure your MPPT unit is set for charging the right type of battery. Check with the manufactuer for the charging voltage of your batteries and set your MPPT to those requirements.6) Ensure your MPPT is located in a well ventilated area as they can get quite warm and the heat needs to escape somewhere. This will also increase the efficiency of the unit. 7) The total distance from the MPPT to the battery and return is critical when working out voltage drop. The wrong size cable can cause major issues. The distance from my MPPT to the batteries was 3.5 metres for a total return distance of 7 metres. I ran 25mm square having worked out the voltage drop over that distance and the amount of maximum current that could be used.

In regard to the inverter. I have little experience with these other than playing with my own inverter. Each installation is different. I would once again highlight the need for a well marked easy reached isolation switch as well as the correct size cable and fuse or Circuit breaker protection. The inverter will also require a well ventilated area due to the heat that requires dissipation. I would also recomend a remote switch to turn the invertor on and off when not in use to save drawing on your batteries as inverters still consume power even when not under load.

Youtube is a wonderful resouce for a lot of information in regard to the above but I must warn you that most of the information I have seen not given by qualified people so beware of what they are saying. At the end of the day its always good having a qualified person go over your work. It may cost a couple of bucks but it great peace of mind. I shudder at some of the electrical work done on boats and scratch my head how more boats have not burnt to the waterline.


Greg H
lagoon 440

[Scrimma]

Originally Posted by ozsailer

Hi Scrimma, while I have an electrical background I am always reluctant to advise people, even in person without seeing what required work is to be undertaken with much of this type of work outside of my qualifications. In saying that I am happy to advise on some aspects of your work.
A couple of things I would raise. 1) Personally I would much prefer your batteries to be next to each other reducing or eliminating having batteries in different locations and othe associated issues such as voltage drop etc 2) I would highly recomend an isoation switch between the solar panels and the MPPT unit to make working on either much easier and safer. 3) You DO require a fuse or circuit breaker between the MPPT unit and your batteries. 4) Ensure you read the manufacturers installation manual on the correct procedure for connecting your solar panels and batteries to your MPPT unit. 5) Also ensure your MPPT unit is set for charging the right type of battery. Check with the manufactuer for the charging voltage of your batteries and set your MPPT to those requirements.6) Ensure your MPPT is located in a well ventilated area as they can get quite warm and the heat needs to escape somewhere. This will also increase the efficiency of the unit. 7) The total distance from the MPPT to the battery and return is critical when working out voltage drop. The wrong size cable can cause major issues. The distance from my MPPT to the batteries was 3.5 metres for a total return distance of 7 metres. I ran 25mm square having worked out the voltage drop over that distance and the amount of maximum current that could be used.

In regard to the inverter. I have little experience with these other than playing with my own inverter. Each installation is different. I would once again highlight the need for a well marked easy reached isolation switch as well as the correct size cable and fuse or Circuit breaker protection. The inverter will also require a well ventilated area due to the heat that requires dissipation. I would also recomend a remote switch to turn the invertor on and off when not in use to save drawing on your batteries as inverters still consume power even when not under load.

Youtube is a wonderful resouce for a lot of information in regard to the above but I must warn you that most of the information I have seen not given by qualified people so beware of what they are saying. At the end of the day its always good having a qualified person go over your work. It may cost a couple of bucks but it great peace of mind. I shudder at some of the electrical work done on boats and scratch my head how more boats have not burnt to the waterline.


Greg H
lagoon 440

Hi Greg. Great info!

The house batteries are just over 600mm apart, but with the cable run, it's closer to 1200mm I would say. Unfortunately I cannot move them closer. I might need to upgrade to a Lagoon 440! I'll run that past the wife!

I think most of those great points you brought up I feel good about...well the ones I can do something about anyway. The main queries would be what size fuse/circuit breaker between MPPT and batteries. The panels max out at just under 6amps each, 54.7w and 327w. There will be 2 of them in parallel, so am I wrong in thinking a 15amp inline breaker on 6awg wire between the MPPT and the battery positive connection be appropriate?

I'll definitely throw an isolation switch in the line between panels and the MPPT. Good reminder!

The location of the MPPT will be within 600mm of the battery connection and in an open rear cabin, along with the inverter, so I feel ventilation should be golden. I can also open 2 small vertical hatches near them to increase cool air flow (not much cool air up here in the tropics, but it'll do something!)

You mentioned return trip from the battery to the MPPT. So if my MPPT is only 600mm away, I should cable for 1200mm? If so, 6awg should still be fine I believe. I'm not sure what size the Victron MPPT can connect to, but I assume 6awg would be about max?! 6awg is good for 37amps from my research, so I could probably go down to 9awg (19amps) or even 10awg (15amps)? Not wanting to cut it too close to the max for the cabling though...

The inverter itself has a kill/power switch on the front of it allowing me to turn it off when it's not in use. My question is, would adding another isolator switch between it and the battery be redundant with the built in off switch that's already on the inverter? I've got a 120amp circuit breaker (that can be manually tripped) for that already to go on the positive line that will run approx 1000mm. Suitable? The inverter is rated at continuous 1000w with a peak of 2000w.

As for youtube...yes, I have learnt ALOT from youtube...but I've started to shy away a little for things that are potentially critical especially electrical issues.

I like your idea of getting a pro to do a quick walk through of the system before it fires up though. I will do that. I hope to iron out as many issues, aswell as learn as much as I can about the systems on my boat (soon to be home).
The brain cells are firing flat out!

[Copacabana]

Following to see the replies concerning wire size...

[LooseGoose]

Hi there.....I am just planning to change over from a PWM charge controller to an MPPT controller on a small system, so I thought I might share some new knowledge.

Here is a link to a resource for calculation of wire sizing

https://www.bluesea.com/resources/1437

Which you might find useful.

You will be feeding 60 plus volts at around 12 amps to the controller in full sun.

However, the way an MPPT controller becomes so efficient as energy harvester is to convert the 50 plus volts down to the 12 to 14 volts needed to charge the battery. It then coverts all that voltage differential intoMORE CHARGING AMPS.

All this to say be careful about wire sizing to the batteries. Your amps will be much higher at 12 volts ... Do the calculation to solve for amps at 650 watts at 14 volts....there are of course losses in the DC to DC conversion, but amps will surely be higher.

Check out this video at 5:17 to see a fellow demonstrate this conversion from high input voltage to battery voltage using meters....you can actually see the amps climb way past nominal amps

https://youtu.be/u4WDBnqrkZU

Your supplier can likely estimate charger output amps so you can size wires and fuses realistically.

Good luck with your project

[Scrimma]

Originally Posted by LooseGoose

Hi there.....I am just planning to change over from a PWM charge controller to an MPPT controller on a small system, so I thought I might share some new knowledge.

Here is a link to a resource for calculation of wire sizing

https://www.bluesea.com/resources/1437

Which you might find useful.

You will be feeding 60 plus volts at around 12 amps to the controller in full sun.

However, the way an MPPT controller becomes so efficient as energy harvester is to convert the 50 plus volts down to the 12 to 14 volts needed to charge the battery. It then coverts all that voltage differential intoMORE CHARGING AMPS.

All this to say be careful about wire sizing to the batteries. Your amps will be much higher at 12 volts ... Do the calculation to solve for amps at 650 watts at 14 volts....there are of course losses in the DC to DC conversion, but amps will surely be higher.

Check out this video at 5:17 to see a fellow demonstrate this conversion from high input voltage to battery voltage using meters....you can actually see the amps climb way past nominal amps

https://youtu.be/u4WDBnqrkZU

Your supplier can likely estimate charger output amps so you can size wires and fuses realistically.

Good luck with your project

Hey! Thanks for that info. I appreciate you taking the time to help a brother out!

From looking at that graph and others i've found on the net (and estimating the length of cable I think i'll need at this point) I'm pretty confident that 6AWG will be more than enough for the solar panel side of the MPPT. I believe it will also be sufficient for the battery side of the MPPT as all tables i can find state the Maximum Amps for Power Transmission is 37amps.
When looking at the VICTRON Smart Solar 100/50, the Power Terminals are stated as 13 mm² / AWG6. So would it be unreasonable to go ahead and use this maximum usable wire to be on the safe side?

Before purchasing the solar panels, I contacted VICTRON and showed them the spec sheet for the Sunpower E-20 327w panels and they replied with the 100/50 being the correct choice but only if the panels are in parallel, otherwise the voltage would be more than the 100/50 can handle. That's no issues with me, so I went ahead and ordered the 100/50 and the 2 Sunpower panels.
When doing the calculation of 650w at 14v comes back at 46.43amps, at 12v it's 54.17amps. Quite a lot of power! This is what confuses me. If Victron told me that this 100/50 be adequate for these panels, then how do I cable big enough to get the 45-55amp max to the batteries when the biggest the controller can receive is 6AWG (37amps)? Or am I completely missing something in all this?

In the video that you shared, i did notice the amps spike to approx double the input amp reading which I understand is because of the MPPT doing its thing to ramp up the output amps because of the extra voltage being supplied by the panels...?

[SpaceRnglr]

Scrimma - Where did you get the SunPower panels? The seem to be hard to find and I will likely want the higher efficiency when I upgrade next year due to lack of space for panels. Thanks!

[Scrimma]

Originally Posted by SpaceRnglr

Scrimma - Where did you get the SunPower panels? The seem to be hard to find and I will likely want the higher efficiency when I upgrade next year due to lack of space for panels. Thanks!

I am in Australia, and there is a company here that sells them for a good price. The company is called Rainbow Power Company.
A link to their site: https://www.rpc.com.au

I called and there are super nice and helpful and have many of these panels in stock along with others. I paid and they shipped the next day. I don't know what their situation is for shipping overseas, but would be worth asking. I asked for a few $ off and they gave me a discount of $100 which was great. The panels were AU$446 each. Pricey, but excellent quality and warranty. They also had the best prices on Victron gear I could find anywhere, online or in a store.

Hope that helps

[SpaceRnglr]

That helps a lot! I’m in Singapore so shipping may not be diabolical... Maybe I could pick some up on a business trip sometime [emoji41]

[Scrimma]

Originally Posted by SpaceRnglr

That helps a lot! I’m in Singapore so shipping may not be diabolical... Maybe I could pick some up on a business trip sometime [emoji41]

Haha yes, if only the carry on bag side was a little bigger!

I should clarify that the $100 they discounted was off the total, which for me meant free shipping a couple states away from them.

I really don't understand why these panels are so hard to come by. RPC were the only one I could find with stock ready to go. They need to turn up the speed on the production line over there in 'merica!