Using an MPPT regulator to charge two separate battery systems

Submitted: Thursday, May 21, 2015 at 19:43
ThreadID: 118932 Views:1544 Replies:3 FollowUps:2
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I have a 100 AH battery in the front RH corner of my van. I have brought a short lead through the floor to an Anderson plug secured to the under side of the floor and protected behind a chassis cross member and a rubber protective plug. A 95 AH house battery just inside the tail gate of my tow vehicle is connected to the battery management system with an Anderson plug.

My solar panels have a capacity of 160 watt (2 x 80) and still has the original regulator and a 6 metre lead - about the size of those that you see on 12V compressors and the like. It works reasonably well but I want a longer lead to reach sunny spots when the van is parked in shade. I thought about 10 metres should do the trick.

I want to fit a MPPT regulator but also want to be able to charge both van and vehicle systems without paying for 2 regulators. So ....
1. Do I need 6 B&S cable or will 8 B&S do?
2. What size MPPT regulator will I need. I am thinking voltage drop here.
3. Is there a particular brand or type of MPPT regulator that lends itself to being placed "in line" as I assume I would need to fit it as near to the end of the cable that plugs into the leads to the batteries as possible. I plan to give it fuse protection.

I will appreciate any comments or suggestions.

Cheers, Kevin
Kevin
It is important to always maintain a sense of proportion

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Reply By: Member - Michael P (QLD) - Thursday, May 21, 2015 at 22:06

Thursday, May 21, 2015 at 22:06
Kevin Hi,
Looks like You and Ruth are getting serious about getting off the beaten track again.
Mike.
AnswerID: 554061

Follow Up By: Kevin S - Life Member (QLD) - Friday, May 22, 2015 at 10:05

Friday, May 22, 2015 at 10:05
HI Mike. You know how it is. If you are not travelling you are thinking about the next trip.

It looks like I will finally be able to retire at the end of this year. If so we plan a looooong trip to the West next year. So we are looking at fine tuning for that event.

Hope you are well. Are you going to the Gathering at Ross River?

Cheers, Kevin
Kevin
It is important to always maintain a sense of proportion

2019 Mitsubishi Cross

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Follow Up By: Member - Michael P (QLD) - Friday, May 22, 2015 at 13:46

Friday, May 22, 2015 at 13:46
Kevin,
Yes off to Ross river, while the van is hooked up will probably go up to Darwin or somewhere. Haven't been up there for a couple of years.
Will You really retire????
Had a coffee this AM with that other Kevin.

Regards Mike.
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Reply By: Member - Alastair D (NSW) - Friday, May 22, 2015 at 07:35

Friday, May 22, 2015 at 07:35
Kevin,
you will get as many opinions as replies but here is my try.

Make sure you feed direct from the solar panel not from the existing regulator. I would put a fuse protected Anderson plug on the panel so the new cable is not permanently connected.

180w means 15A flow at 12v therefore I will use this for the peak feed current.

At 15A 6BS will drop 0.21v over the 10m length whereas 8BS will drop 0.34v. This drop is not a problem in either case but obviously the heavier cable is slightly better.

You will need a regulator that is well above the maximum of your panels if you wish it to be reliable long term. Electronics and heat do not like each other. I would go for a 300w regulator. This also allows some margin if you add or change panels in the future.

Be aware that some of the cheaper regulators that are advertised as MPPT on the web are fakes and are really just cheap PWM units inside. Buy a brand name one to be sure. Most of the better ones come with settings for different battery chemistries and have a small readout. Most people find it compulsive to keep checking what output they are getting and it is interesting to see the changes. It also helps to get the position and angle right.

You are correct that the reg needs to go near the battery. Personally I would permanently mount the reg and have a convenient connector to plug the lead in. This avoids clips which I hate and makes the install simple neat and safer. Perhaps buy a cheap plastic tool box into which the cable will fit when coiled and mount the reg to it. This makes for a neat solution. By the way when buying the cable look for a nice flexible type - it will have more but thinner strands. The stiffer type will fatigue over time when you fold/coil it and break strands inside leading to higher voltage loss.

Jaycar used to sell some good cable in this size.

I have no opinion re the brand but I would go and have a look at some better brands and then search for the best price once you have got a shortlist.

hope this helps
AnswerID: 554066

Reply By: Member - Boobook - Friday, May 22, 2015 at 09:35

Friday, May 22, 2015 at 09:35
1. Do I need 6 B&S cable or will 8 B&S do?

If you remove your current regulator, and run wires from the panels to a MPPT regulator near the batteries then 8 B&S is plenty, while there will be a voltage drop the MPPT will accommodate this and fully charge the batteries. You must use decent cable from the reg to the batteries and keep that as short as possible. Throw the old reg in the bin.

2. What size MPPT regulator will I need. I am thinking voltage drop here.

20A is a good size. Your panels will charge at up to 12A approx. This has little to do with the voltage drop though.

3. Is there a particular brand or type of MPPT regulator that lends itself to being placed "in line" as I assume I would need to fit it as near to the end of the cable that plugs into the leads to the batteries as possible. I plan to give it fuse protection.

I like the Tracer ones, True MPPT You can get them on ebay from $130ish. They are resold by Projecta and co for twice the price. Avoid Juta like the plague. they say they are mppt but are not.

There are lots out there, the Tracer is the one I have and tested it really is MPPT.
AnswerID: 554070

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