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Old 07-02-2019, 01:25   #1
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Q? Solar/MPPT/2 banks and a Battery Isolater

What to do? OK no such thing as a silly question just silly people but here we go...

Present situation... 2 x 50W panels.... a PWM controller ... feeding just the house bank.

Not normally an issue as I have two banks "Engine' 1 x 115 Ah, 'House' 1 x 230 Ah, which I always run with the switch at 1+2 so any solar finds its way to all three batteries.

When she is laid up alongside and on the grid switch is set to 'Off' and all 3 batteries are charged by shore power...

Recently however she was laid up alongside with no shore power and with the batt switch to 'Off' only house was getting benefit of solar...'engine' was left to its own devices.... This is the sort of problem you don't realise you have until it manifests itself.....

So I am currently overhauling her electrical system which has suffered major 'equipment creep' over the last 25 years.

I was planning to fit a Victron MPPT such as this one https://12volttechnology.com.au/sola...bluetooth.html

And I was also thinking of fitting one of these... https://www.solar4rvs.com.au/argo-fe...ttery-isolator

Now the question... that unit is designed to take 100 A from an alternator... is it overkill for a system where we are dealing with less than 10 A?

Not that the $$$$ are a real issue ( yes cheaper is always often better ) but is there a better way?

Thankee..
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Old 07-02-2019, 01:57   #2
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Re: Q? Solar/MPPT/2 banks and a Battery Isolater

A big thumbs up for the Victron, we have two but only because it was easier to wire up our panels that way. You might stretch for the 15/75 if you plan to increase the solar panels as this would provide some future proofing. I do like the app with them to see exactly what is going on and see the charging history.

To combine the engine and house batteries we have a VSR. Solar connected to house and when the bank has reached 13.7v (I think) the VSR kicks in and connects the engine battery in circuit. The VSR is from BEP, but there are lots of others and cheaper than a battery to battery widget.

Note we did have one problem. Initially I wired the solar to the engine start battery as recommended by BEP. However, what happens is the engine battery charges up to 13.7 volts and the VSR connects engine battery to the house with a big clunk. The discharged house bank then pulls down the engine battery voltage and the VSR disconnects when the voltage drops below 12.8v with another big clunk, repeating every couple of minutes. This became quite annoying so I moved the solar to the house bank and peace was restored.

http://www.ebay.co.uk/i/153199449890

or

https://www.kiravans.co.uk/catalog/p...fo.description

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Old 07-02-2019, 02:44   #3
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Re: Q? Solar/MPPT/2 banks and a Battery Isolater

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Originally Posted by El Pinguino View Post
And I was also thinking of fitting one of these... https://www.solar4rvs.com.au/argo-fe...ttery-isolator

Now the question... that unit is designed to take 100 A from an alternator... is it overkill for a system where we are dealing with less than 10 A?

Not that the $$$$ are a real issue ( yes cheaper is always often better ) but is there a better way?

Thankee..
Unfortunately there is a good chance the splitter will not work. The problem that there is 0v on the input pin when idle. No problem for an alternator, but it causes issues with most solar controllers. Controllers generally require or at least expect to see a battery voltage at start up.

A VSR will work.

So cheaper is better .
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Old 07-02-2019, 11:36   #4
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Re: Q? Solar/MPPT/2 banks and a Battery Isolater

Many thanks Pete and Noelex,

A VSR it is then.....
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Old 08-02-2019, 11:14   #5
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Re: Q? Solar/MPPT/2 banks and a Battery Isolater

I have made a cable with a Crocadile Clip on each end (Look away noelex 77) for just this scenario and parallel the two batteries so that solar tops them both up while laid up. The only problem I have had is finding the cable each autumn!
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Old 08-02-2019, 12:14   #6
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Re: Q? Solar/MPPT/2 banks and a Battery Isolater

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Originally Posted by Rapanui View Post
Look away noelex 77
.

My eyes are suitably averted.

Actually, I think manually linking the batteries to share the solar supply can be a good solution. While I understand using jumper leads, a better way of doing this is with a battery switch that parallels the house and start batteries. This prevents wrong connections, sparks, nothing to lose etc. Essentially this is just permanently wiring the jumper leads.

The solar panels can be permanently connected to the house bank. Simple. When required, operating the battery switch will parallel the start and house banks, fully charging the start bank. This can also be used when leaving the boat for extended periods, ensuring solar replaces the self discharge of the start bank.

A VSR does this automatically, but these devices do fail more often than a simple battery switch. The battery switch will also allow the house bank to start the engine, so it has a dual function.

The start bank has very little draw. Over complicating the charging of this bank is not always the answer in the goal for reliability. A VSR for the solar supply is a great solution for many boats, but do not entirely dismiss a simple, manual battery switch that will parallel the solar supply to the house and start banks.
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Old 08-02-2019, 12:50   #7
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Re: Q? Solar/MPPT/2 banks and a Battery Isolater

A friend, who has a near sister of my boat, has just advised me that you can use the Victron Argo FET . Seems you just need the "Ground" and "Energize" pins connected to make it work.


He also suggested I go RTFM which sounds a bit rude so I don't think I will go quite that far.....
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Old 08-02-2019, 17:13   #8
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Re: Q? Solar/MPPT/2 banks and a Battery Isolater

I've had great results using this Victron Cyrix unit to prioritize my main refrigerator vs inverter batteries.

Flawless for 6 months on a 272 watt system.
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