MPPT Battery Connection on Dual Batteries?

[Uncle Bob]

Originally Posted by Scrimma

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!

I believe that their panels are made in Malaysia, Philippines, Mexico and China.

[Scrimma]

Originally Posted by Uncle Bob

I believe that their panels are made in Malaysia, Philippines, Mexico and China.

Indeed you are correct sir! I was confusing victron with sunpower. Now saying that, victron is probably manufactured elsewhere too! Haha. Either way, good products whoever is clocking them all together.

[noelex 77]

Ideally the positive feed should be taken from one battery, and the negative feed from the other battery. Not both from the same battery as your diagram shows. See picture.

This reduces voltage imbalances between the batteries, but also means if I understand your system correctly, that the wire from the solar controller to the battery will be shorter on one side. This will help reduce the voltage drop between the controller and the batteries.

With 45A under ideal conditions , 6AWG wire is just OK from a current carrying capacity, but it is unlikely to be OK from a voltage drop stand point. Especially if you have a longer run, you will need to use a larger diameter wire between the controller and the batteries. The distance has to be measured before this size can be calculated.

There are various ways to reduce the wire size, just before it enters the controller. Perhaps start another thread on this topic.

[Scrimma]

Originally Posted by noelex 77

Ideally the positive feed should be taken from one battery, and the negative feed from the other battery. Not both from the same battery as your diagram shows. See picture.

This reduces voltage imbalances between the batteries, but also means if I understand your system correctly, that the wire from the solar controller to the battery will be shorter on one side. This will help reduce the voltage drop between the controller and the batteries.

With 45A under ideal conditions , 6AWG wire is just OK from a current carrying capacity, but it is unlikely to be OK from a voltage drop stand point. Especially if you have a longer run, you will need to use a larger diameter wire between the controller and the batteries. The distance has to be measured before this size can be calculated.

There are various ways to reduce the wire size, just before it enters the controller. Perhaps start another thread on this topic.

Good evening sir and thank you for your wisdom. All good info and I've taken note. I do have another question though that may help out this whole mess. What do you think of i installed my mppt right next to my inverter and then had VERY short cable run (300-400mm) to the battery connections on the back of my inverter. The inverter is in no way connected to the A/C panel. It's just a regular inverter that I can plug into if needed (1000w continuous, 2000w peak). The inverter is wired to the battery that isnt connected directly to the house load/draw, so having the mppt pushing into that positive should help out any equalization issues? Or will that just create the same problem but in the other direction? Also, the inverter negative is running to the shunt (2m away) to monitor loads etc through my battery monitor, and that cable, along with the positive cable can effectively be used as the mppt to battery cables. The inverter cables are oversized at 2AWG (2B&S) so will carry all the amps that the controller can throw at it and then plenty more. I feel like this could be the unicorn solution I've been searching for...but I'm still learning. What do you think?

[noelex 77]

It is not ideal, but it is acceptable, especially if the inverter is only used infrequently and/or for low loads.

Don’t forget that the 6 awg wire to the solar controller will need its own fuse or circuit breaker, as the fuse for the inverter will be too large for this gauge of wire.

This solution still leaves you with the batteries wired incorrectly (both load leads from the same battery). Given (if I understand correctly) the long distance between the batteries, this will have some practical impact on your battery life.

Boat wiring is rarely perfect and at least this fault is not a safety concern, but installing 654W of solar means in the future you will become a boat that can use quite a reasonable amount of power and because you can you will .

Many older boats were conceived with a very basic, low demand electrical system. Moving to greater demand with higher currents sometimes needs a rethink. This might be a good time to have a professional (and I am not a professional so I have no axe to grind) look over the total electrical system and provide some recommendations. Ideally the time to do this is before the solar installation.

However, please do not be put off asking questions on the forum. There are many knowledgeable professionals who kindly provide free advice. The limitation is that it is difficult in forum posts to gain an overall picture of your electrical system and I think it is time for a more holistic approach.

[Scrimma]

Originally Posted by noelex 77

It is not ideal, but it is acceptable, especially if the inverter is only used infrequently and/or for low loads.

Don’t forget that the 6 awg wire to the solar controller will need its own fuse or circuit breaker, as the fuse for the inverter will be too large for this gauge of wire.

This solution still leaves you with the batteries wired incorrectly (both load leads from the same battery). Given (if I understand correctly) the long distance between the batteries, this will have some practical impact on your battery life.

Boat wiring is rarely perfect and at least this fault is not a safety concern, but installing 654W of solar means in the future you will become a boat that can use quite a reasonable amount of power and because you can you will .

Many older boats were conceived with a very basic, low demand electrical system. Moving to greater demand with higher currents sometimes needs a rethink. This might be a good time to have a professional (and I am not a professional so I have no axe to grind) look over the total electrical system and provide some recommendations. Ideally the time to do this is before the solar installation.

However, please do not be put off asking questions on the forum. There are many knowledgeable professionals who kindly provide free advice. The limitation is that it is difficult in forum posts to gain an overall picture of your electrical system and I think it is time for a more holistic approach.

Words of wisdom. Thank you! Yeah the batteries ar not ideal with how they are wired. They are 2x260ah fullriver sealed batteries. They have been in for at least 7 years, so it will be interesting to see how long they last once living aboard with this solar. Once they finish their service life I fully intend on a dressing that issue. It would be great to do it now, but I'm against the wall for time with everything else at the moment.

Yes the inverter will be used for charging power tools, the wife's power hungry design laptop, maybe a hair dryer or straightener from time to time (I think the wife will get sick of doing that when living on a boat...but time will tell!). So yes, relatively little use. I've got a 50a inline breaker for the positive from the charge controller to the inverter, and a 20a 2 post noak breaker for the wife's between panels and inverter. I also have a 120a breaker from the inverter to the battery positive. How does all that sound? All those breakers can be manually flicked to allow isolation of components etc.

Haha yes, I am planning ahead with this amount of solar on the rack. I figure I can live on next to no power, but some creature comforts keeps the admiral happy. Happy admiral, happy life!

Getting a pro to come take a look is definitely on the list in the coming months.

[Pete7]

Originally Posted by Scrimma

Words of wisdom. Thank you! Yeah the batteries are not ideal with how they are wired. They are 2x260ah fullriver sealed batteries. They have been in for at least 7 years, so it will be interesting to see how long they last once living aboard with this solar.

You are on borrowed time and probably only getting away with it because you are not currently living on board. On the positive side (sorry pun intended ) you have some serious clout in those panels, so if you minimise night time use, you might eke out a bit more time.

However, stand by for imminent failure, watch them like a hawk especially for them getting hot with that much power going in. Safe option, replace now if in the near future you will be away from civilisation making the replacement all so much more difficult.

Pete

[Scrimma]

Yeah, I think I'm definitely running at the end of their life. Although, they are still strong in the volts department and prior to purchasing this vessel a couple months ago, the previous owner used it once a week for twighlight racing with the only real draw being the very rare weekend spent on it with his wife and the LED anchor light between the weekly races. I'm feeling optimistic, probably foolishly, they they have a few legs left in them yet. When the time comes though, I plan on going with a couple drop in lithium batteries to the tune of around 400ah house. I'm sure there will be a myriad of problems to figure out once that happens! That's when I'll get all the parallel wires set up correctly for better balanced charging and will need to invest in a new charger for when I turn the motor on that has lithium charging algorithms. Money money money. Whoever said B.O.A.T. means bring out another thousand was wrong. It's being out another 5k!

Thankfully no long sails planned at this stage. Will spend the next 8 months or so around the Whitsunday islands and the reef in Australia (never more than a days sail from port) then head down the East coast as cyclone season rolls around in Nov/Dec.

[LooseGoose]

Originally Posted by Scrimma

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...?

Pleased you were able to watch the video and get the point of what these great charge controllers actually do for a living. I believe the controller is called at 50 amps out......it will put that out and no more, safely discarding excess power, so I don't think you have any concerns there. It will be a very rare occasion to see full amps from the panels. And don't forget voltage drop from panels to controller, as well as the fact power is also degraded in the DC to DC voltage conversion.

You'll be fine with #6. Just monitor the cables by feeling how warm they get on bright sunny days, and don't leave the system running unattended until you have physically experienced your peak conditions.

Your Manuel's will likely come with MC4 connectors. I have four it easy and useful to use a dedicated outdoor rated MC4 solar cable with factory ends to be a great way to get power fed into the boat. Buy the premade cable long enough for the home run distance to and from the controller, it will have a male and a female end....cut it in half and enjoy factory waterproof connections and outdoor rated cabling.

The Klein CL800 meter measures DC amps via clamp......very very useful on a boat, and will confirm what's going on in any wire....no guessing.

Digital Clamp Meter AC/DC Auto-Ranging 600 Amp Measures Voltage, Resistance, Temp, More Klein Tools CL800 https://www.amazon.com/dp/B019CY4FB4..._jkFxCbHBTX9TA


Best of luck with your project.

[Scrimma]

After looking into mc4 cables I order some 6mm mc4 lengths, a couple of mc4 T connectors to easily clip into parallel, some online fuses/breakers etc. Should be good to go. I'll use the 6AWG for the approx 300mm-400mm run to the power terminals for the inverter which will the carry the current along much heavier cables to the battery and shunt. It's all coming together...slowly!
That amp meter looks like a fantastic piece of gear for monitoring! Thank you.

Additionally, Thank you to you and all who take some time of your days to help people out on these forums. It's a huge resource and I'm very grateful to you all!

[Pete7]

There is a little tool kit for MC4 connectors which is handy to take them apart and fit.

https://www.amazon.co.uk/gp/product/...?ie=UTF8&psc=1