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Running two solar controllers / arrays


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If running through one controller ie 40 amp instead of the a 20 amp remember to upgrade the cable from the controller to the battery, so you don't get a bigger volt drop, and to upgrade the fuse! 

 

As a addition the percentage charge displays on any solar controller are lying to you, they have no idea of amps out of the battery only out of themselves so don't know how much is charging the battery and how much is feeding inverters fridges pumps etc.

 

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4 hours ago, Detling said:

 

 

As a addition the percentage charge displays on any solar controller are lying to you, they have no idea of amps out of the battery only out of themselves so don't know how much is charging the battery and how much is feeding inverters fridges pumps etc.

 

Like most percentage meters

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16 hours ago, Detling said:

the percentage charge displays on any solar controller are lying to you,

 

12 hours ago, ditchcrawler said:

Like most percentage meters

96% of percentage meters tell porkies according to my percentage meter accuracy percentage meter.

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oh god..i can't believe I'm going to continue this on... so what would be the easiest way to obtain an accurate state of charge meter??   Just seems if one is going to the effort of maximising the solar charge capacity, I should probably try and have a way of knowing how it is performing and when our demands are outstripping supply.

 

 Ideally something that can be read from a panel, rather than requiring a phone app etc.....?

 

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11 minutes ago, TandC said:

oh god..i can't believe I'm going to continue this on... so what would be the easiest way to obtain an accurate state of charge meter?? 

If you can design one - you'll make 'millions'.

 

The battery capacity changes almost daily, all you can do is do a manual capacity check (say) weekly or monthly.

 

You can accurately tell when the battery is 'fully' charged, but there is no accurate 'meter' method of determining capacity.

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I have a similar (older) setup wired like this:

 

                  ______________________ To controller + in

                 +    

             100W

                 -     

     --------+--------

     +                      +

  150W                150W

     -                       -

     --------------------------------------- To controller - in

 

Drawn in ASCIICAD (tm) (unofficial copy)

 

The two identical panels are in parallel to avoid voltage difference issues.

The older 100W panel is at the front of the boat, the remainder at the rear and I get charge even when half the boat is in the shade.

Worked great for 7 years now

Newer panels are far more efficient and I will get around to upgrading (one day...)

And don't forget to put a fuse inline between the controller and the batteries.

 

Edited by Duck-n-Dive
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4 hours ago, TandC said:

what would be the easiest way to obtain an accurate state of charge meter??

A SmartGauge.  But it only works accurately on discharge (arguably when you need it most). 

 

To determine SoC when charging, look for the charge current to be around 1% of the bank capacity when charging at a voltage above 14.2V. You may find that the SmartGauge tracks the SoC when charging quite closely, but it can be up to 10% out.

 

Note that this measurement is of charge current into the batteries, not a total of what the panels are putting out, as they might be supplying other consumers (lights, pump etc).

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5 hours ago, TandC said:

so what would be the easiest way to obtain an accurate state of charge meter?? 

 

 Ideally something that can be read from a panel, rather than requiring a phone app etc.....?

 

It is generally accepted that lead acid batteries are as good as full when they are drawing only 2% of capacity, (some prefer to use 1% of capacity), when the charging voltage is 14.4V.

 

I have a NASA BM2 which shows Amps being drawn by the battery when charging, along with the voltage. It has a stab at SOC %age, but it is as much use as a chocolate fireguard.

 

Given that the actual capacity of a battery bank is going to change, (fall), over time, it is difficult to be certain of capacity. You can do tests with a lightbulb, or you can make an educated guess. With a 450Ah bank of Trojan T105s, I used to consider them definitely full if they were drawing 4A at 14.4V when charging. Even if their capacity was a bit less than 50% of nominal when new, this was still a bit less than 2% of capacity.

 

I also have a Smartgauge and would advise anybody with one to ignore what it says when it is reading over 80%, and to definitely not consider their batteries as full when it reads 100% when charging. A Smartgauge is good for telling you when you need to start charging, but not when you can stop.

 

If you have the money for one, but not both, get the NASA BM1 or BM2

 

If you have the money for both, get a Victron BMV712 :) 

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10 minutes ago, Richard10002 said:

It is generally accepted that lead acid batteries are as good as full when they are drawing only 2% of capacity, (some prefer to use 1% of capacity), when the charging voltage is 14.4V.

 

I have a NASA BM2 which shows Amps being drawn by the battery when charging, along with the voltage. It has a stab at SOC %age, but it is as much use as a chocolate fireguard.

 

Given that the actual capacity of a battery bank is going to change, (fall), over time, it is difficult to be certain of capacity. You can do tests with a lightbulb, or you can make an educated guess. With a 450Ah bank of Trojan T105s, I used to consider them definitely full if they were drawing 4A at 14.4V when charging. Even if their capacity was a bit less than 50% of nominal when new, this was still a bit less than 2% of capacity.

 

I also have a Smartgauge and would advise anybody with one to ignore what it says when it is reading over 80%, and to definitely not consider their batteries as full when it reads 100% when charging. A Smartgauge is good for telling you when you need to start charging, but not when you can stop.

 

If you have the money for one, but not both, get the NASA BM1 or BM2

 

If you have the money for both, get a Victron BMV712 :) 

 

If you have a Smartgauge and a battery monitor which shows amp hours used, you can assess battery capacity by taking a fully charged battery down to 50% on the Smartgauge, then noting the amp hours used and doubling it.

 

You can also discharge to a higher value and multiply the amp hours used accordingly, for example discharge by 20% and multiply by 5, discharge by 25% and multiply by 4 etc.

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6 minutes ago, cuthound said:

 

If you have a Smartgauge and a battery monitor which shows amp hours used, you can assess battery capacity by taking a fully charged battery down to 50% on the Smartgauge, then noting the amp hours used and doubling it.

 

You can also discharge to a higher value and multiply the amp hours used accordingly, for example discharge by 20% and multiply by 5, discharge by 25% and multiply by 4 etc.

Sorry - of course you can, and that was how I made my educated guesses :)

 

and how I came to know that I am a destroyer of lead acid batteries, no matter how anal I was with regards to a charging regime :( 

 

 

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9 minutes ago, cuthound said:

If you have a Smartgauge and a battery monitor which shows amp hours used, you can assess battery capacity by taking a fully charged battery down to 50% on the Smartgauge, then noting the amp hours used and doubling it.

Yup.  Absolutely THE easiest way to measure battery capacity.

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12 hours ago, TandC said:

oh god..i can't believe I'm going to continue this on... so what would be the easiest way to obtain an accurate state of charge meter??   Just seems if one is going to the effort of maximising the solar charge capacity, I should probably try and have a way of knowing how it is performing and when our demands are outstripping supply.

 

 Ideally something that can be read from a panel, rather than requiring a phone app etc.....?

 

A voltmeter and an ammeter

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27 minutes ago, ditchcrawler said:

A voltmeter and an ammeter

Get a Victron BMV battery monitor. It does both voltage and amps in so can easily be used to monitor tail current decrease. Ignore the SoC reading though. None of them work on telling you when the batteries are fully charged.

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11 hours ago, Dr Bob said:

Get a Victron BMV battery monitor. It does both voltage and amps in so can easily be used to monitor tail current decrease. Ignore the SoC reading though. None of them work on telling you when the batteries are fully charged.

 

The SoC reading on  Victron BMV can me made to read reasonably accurately.

 

You just need to:

 

1. Reset the BMV to 100% when the batteries actually are at 100% monthly, and,

 

2. Reset the battery capacity to the measured the capacity annually.

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1 hour ago, cuthound said:

 

The SoC reading on  Victron BMV can me made to read reasonably accurately.

 

You just need to:

 

1. Reset the BMV to 100% when the batteries actually are at 100% monthly, and,

 

2. Reset the battery capacity to the measured the capacity annually.

 

Agreed (Post #31) but I suggested monthly.

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On 07/07/2020 at 09:29, Duck-n-Dive said:

I have a similar (older) setup wired like this:

 

                  ______________________ To controller + in

                 +    

             100W

                 -     

     --------+--------

     +                      +

  150W                150W

     -                       -

     --------------------------------------- To controller - in

 

Drawn in ASCIICAD (tm) (unofficial copy)

 

The two identical panels are in parallel to avoid voltage difference issues.

The older 100W panel is at the front of the boat, the remainder at the rear and I get charge even when half the boat is in the shade.

Worked great for 7 years now

Newer panels are far more efficient and I will get around to upgrading (one day...)

And don't forget to put a fuse inline between the controller and the batteries.

 

At best you have a 250 watt solar system there, the current is going to be limited to 5 ish amps by the 100 watt panel it will not allow any more through, so the 150 watt panels which probably are each capable of 6 or more amps ie 12+ in parallel, are being limited to 5 amps total maximum, you would get more solar power by just shorting out or removing the 100 watt panel, provided the controller can cope with 300 watts and 12+ amps input.

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17 minutes ago, Detling said:

At best you have a 250 watt solar system there, the current is going to be limited to 5 ish amps by the 100 watt panel it will not allow any more through, so the 150 watt panels which probably are each capable of 6 or more amps ie 12+ in parallel, are being limited to 5 amps total maximum, you would get more solar power by just shorting out or removing the 100 watt panel, provided the controller can cope with 300 watts and 12+ amps input.

Yes this is true whenever all panels are getting the same sunshine, but when half the boat is in shade then I still get some power.  It is a compromise and I will rectify this when it approaches page 1 of my "to do" list ?

Edited by Duck-n-Dive
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2 hours ago, Alan de Enfield said:

 

Agreed (Post #31) but I suggested monthly.

 

Unless you really, really abuse a lead acid battery its capacity is unlikely to change significantly in a week. Same over a single month or two unless you are not fully recharging it every significant discharge.

 

My Lifeline AGM's are 12.5 years old now and still have about 40% of their original capacity left. They were at 65% of their original capacity when I bought the boat at 6.5 years old.

 

I will keep them until they can no longer support the boat overnight, but given the eye watering cost of Lifeline's now, will probably replace them with something else.

 

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20 hours ago, cuthound said:

given the eye watering cost of Lifeline's now, will probably replace them with something else.

Is it really eye watering when amortised over 13+ years?

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On 05/07/2020 at 16:27, Jen-in-Wellies said:

I'll ask again. What are the open voltages of the panels? If they are the same, say around 19V on all, then they can be wired in parallel fine. If the 320W panel has twice the open circuit voltage of the 100W panels, then the two 100W's can be wired in series, then in parallel to the 320W. All in to one controller.

 

Point of order, it is matching the Vmp that is relevant, not the Voc, although to be fair if one is matched the other is not likely to be too far off.

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5 hours ago, WotEver said:

Is it really eye watering when amortised over 13+ years?

 

I have 4 of these for my leisure batteries so replacement over £1600 for 450 Ah, plus 3 x 12 volt batteries for the starter and BT.

 

https://www.tayna.co.uk/marine-batteries/lifeline/?ordering=&A-8=6&A-22=220

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On 08/07/2020 at 12:33, cuthound said:

Same over a single month or two unless you are not fully recharging it every significant discharge.

According to battery manufacturers every discharge is 'significant' - boaters usually use 50%, but this is just an arbitrary figure that appears to give the best balance between Cost / Life

 

But - not fully recharging back from (say) 50% SoC every 2 days (repeatedly) is going to have a fairly big cumulative impact over a relatively short period.

 

There seems to be more and more boaters talking about their battery banks as having just two 'domestics'. Assuming these are 110AH, and, assuming an 'average' daily consumption of 100AH (which is probably not an unreasonable number) then every two days they will be at 50% SoC and require (possibly) 8+ hours charging, the recommended "4 hours per day" will mean that they progressively get deeper and deeper discharged.

Solar will obviously have a positive effect for the Summer months.

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