Extending solar power

[Dr Bob]

2 hours ago, WotEver said:

Sorry but no, they don’t ‘have to’ be linked. Some controllers have that facility, which may give extra control over simply paralleling up the outputs. 

I was going to write an explanation as to why it works just fine with two (or more) controllers in parallel but I just came across this website which explains it well enough and even gives a video demonstration. 

https://www.altestore.com/blog/2016/08/wiring-solar-charge-controllers-in-parallel/

All they will do is to sum their outputs just like having two alternators in parallel. Once the charging is out of the bulk phase and into absorption then one controller might take over the bulk of the charge but that’s not a huge problem if the batteries are already up to 80%-ish. 

Thanks for that. A fairly simplistic explanation in the video - and assume it is true.

.....but can you help explain what is likely to happen with charge rates as we near fully charged. I dont understand exactly what 'tail' current I should have on my cheapo lead acids to indicate 100% SoC as the current is different from my 3 charging sources ie Victron combi battery charger, sterling atob/alternator and solar. My battery bank is 660Ahrs now 12 months old and I have 200W of solar. The bit I am interested in is the last 5% of capacity (95-100% SOC) as that is what the solar is aimed at. Overnight I typically use say 100Ahrs and a couple of hours cruising with the engine on will put back in say 60Ahrs so with efficiciency losses I need another 60-70Ahrs. Lets take this as the example.

After a couple of hours with the engine on, the current is dropping to 10-12A (14.4V) and then it goes into float mode. Very similar performance with the Victron when back on shore power. If I force either charge device back on for a second or third time, the tail current typically shows up as 3-5A  which is less than 1% of capacity. At this point though I am very doubtful if I have put in that 60-70Ahr needed to balance what I took out the night before (ie if you plot a graph of A vs Time and then integrate - or measure area under graph) yet the tail current is less than 1% capacity. Now, lets introduce solar. In parrallel with the engine charge, there is solar going in all the time (assume its summer!). What I find is that once the alternator or battery charger is off, the solar shows 10A+ if it is sunny regardless of the state of charge and even if the engine/shore power charge is <1% of tail current. Now the current solar set up only gives up to around 11A max, although there is normally circa 2A going out all the time as the inverter is powering the 240v fridge hence the actual solar charge is likely 14A. What I am confused about is the tail current of 11A with the solar but this drops to 3-5A if either charger is on.

By doubling the size of the solar I should be able to get nearer 30A in on a sunny day which then is likely to be reduced by the demand of the batteries but is the tail current then going to be say 10A as per now as the SoC reaches 100%. My reason for putting more solar on is that I then dont have to run the engine each day and there is more chance of getting a decent solar charge on cloudy  or spring/autumn days.

Aplogies for the ramble - I am mixing two issues.

- the difference in tail current with a higher tail current seen on solar

- I never seem to be able to reconcile Ahrs out with Ahrs back in (always too little back in) although the battery SoC must be near 100% most days as the batteries are still in good nick - 90% of original capacity after 1 year (and not tried de-sulphating yet).

[WotEver]

What voltage is the Solar showing when tail current is at 10A?

What voltage is the alternator/charger giving when tail current is at <1%?

if the Solar voltage is higher, that explains the higher current. At these temps (close to 0C) the tail absorption voltage should ideally be 15V+ if wet batteries. 

1 hour ago, Dr Bob said:

I never seem to be able to reconcile Ahrs out with Ahrs back in (always too little back in) although the battery SoC must be near 100% most days as the batteries are still in good nick - 90% of original capacity after 1 year (and not tried de-sulphating yet).

If you’re regularly charging to 95%+ then you won’t be harming the batteries too much. 

[WotEver]

1 hour ago, Dr Bob said:

the current is different from my 3 charging sources

That can only be because the voltage is different. Think of the charger as voltage source and the battery as a resistor. E=IR and all that, so with a fixed load (battery) the only way I can be bigger is if E is bigger. 

[peterboat]

4 hours ago, WotEver said:

Sorry but no, they don’t ‘have to’ be linked. Some controllers have that facility, which may give extra control over simply paralleling up the outputs. 

I was going to write an explanation as to why it works just fine with two (or more) controllers in parallel but I just came across this website which explains it well enough and even gives a video demonstration. 

https://www.altestore.com/blog/2016/08/wiring-solar-charge-controllers-in-parallel/

All they will do is to sum their outputs just like having two alternators in parallel. Once the charging is out of the bulk phase and into absorption then one controller might take over the bulk of the charge but that’s not a huge problem if the batteries are already up to 80%-ish. 

Tony its a blog, all I know is with two tracers I used to get boiling batteries. I spoke to midnite controllers they said if paired comms cable needed to make sure batteries not cooked, I believe them because they have been in the business for years other distributors said the same,  so I purchased a controller what could do the job and batteries dont boil anymore so I believe what I see

[WotEver]

1 minute ago, peterboat said:

Tony its a blog

Yet correct. 

2 minutes ago, peterboat said:

all I know is with two tracers I used to get boiling batteries.

Yet with no explanation as to why. 

Obviously Midnight or any other controller supplier will be happy to sell you a nice shiny bigger new one. Where is their evidence as to why that is necessary?

[peterboat]

9 minutes ago, WotEver said:

Yet correct. 

Yet with no explanation as to why. 

Obviously Midnight or any other controller supplier will be happy to sell you a nice shiny bigger new one. Where is their evidence as to why that is necessary?

Because they went to all expense of making all their controllers have comms ports so that they can control other controllers nobody does that without good reason [ie they dont want to be sued when they shag your batteries!]

[WotEver]

2 minutes ago, peterboat said:

nobody does that without good reason

It’s hardly difficult. 

It enables them to prevent one of the controllers from shutting down once the charge gets into absorption. Afaik it doesn’t offer much more than that. 

If their controllers are boiling batteries then they deserve to be sued! It’s pretty fundamental that a charger shouldn’t do that!

[peterboat]

2 minutes ago, WotEver said:

It’s hardly difficult. 

It enables them to prevent one of the controllers from shutting down once the charge gets into absorption. Afaik it doesn’t offer much more than that. 

If their controllers are boiling batteries then they deserve to be sued! It’s pretty fundamental that a charger shouldn’t do that!

But two operating together dont do what one on its own does, I used to watch the two meters on the tracers and its like they didnt know what to do up and down all the time. Me I have had solar for thirteen years and that was the only time I had problems, I sold both of the tracers and on their own both worked ok, so no issues with the controller

Anyway the problem for me is sorted I had to take the batteries out, have them checked over and the acid redone and since then on one controller no issues

[Richard10002]

Dr. Bob.....

Tail current can be confusing:

The tail current recognised as indicating that your batteries are full should be monitored at a particular voltage during the absorption phase. BULK - ABSORPTION - FLOAT

I use 14.4V as I read it on the Smartgauge Web site a few years ago.

When your alternator and shore power are in float mode, the voltage will be a bit over 13V, which is why the current is lower than when your solar is showing 14V or more.

My Sterling shore charger tends to revert to float after  only an hour, which is never enough to get the tail current down... so I turn it it off and on to start the hour again. I also set my phone for a 55 minute alarm so I can check the current before it reverts to float. I turn it on and off again if necessary.

[WotEver]

14 minutes ago, Richard10002 said:

I use 14.4V as I read it on the Smartgauge Web site a few years ago.

Gibbo wouldn’t disagree with 15V at winter temps at the end of charge. But 14.4V will just about do the job. 

[WotEver]

44 minutes ago, peterboat said:

But two operating together dont do what one on its own does, I used to watch the two meters on the tracers and its like they didnt know what to do up and down all the time.

Sounds to me like they need to go back to the drawing board with those then and pull them from sale. 

Seeing as you don’t like blogs, here’s Morningstar’s observations:

https://www.morningstarcorp.com/parallel-charging-using-multiple-controllers-separate-pv-arrays/

[Dr Bob]

2 hours ago, WotEver said:

That can only be because the voltage is different. Think of the charger as voltage source and the battery as a resistor. E=IR and all that, so with a fixed load (battery) the only way I can be bigger is if E is bigger. 

Yes, I understand and agree. The victron/Sterling are at 14.4V but the solar mppt tends to be 0.2-0.3v higher. That could explain the difference in tail currents. It will be interesting to see how it works out with the extra panels. I am still somewhat confused over balancing what has gone in and out and will take somemore detailed notes once we get back out sailing more often.

 

1 hour ago, Richard10002 said:

Dr. Bob.....

Tail current can be confusing:

The tail current recognised as indicating that your batteries are full should be monitored at a particular voltage during the absorption phase. BULK - ABSORPTION - FLOAT

I use 14.4V as I read it on the Smartgauge Web site a few years ago.

When your alternator and shore power are in float mode, the voltage will be a bit over 13V, which is why the current is lower than when your solar is showing 14V or more.

My Sterling shore charger tends to revert to float after  only an hour, which is never enough to get the tail current down... so I turn it it off and on to start the hour again. I also set my phone for a 55 minute alarm so I can check the current before it reverts to float. I turn it on and off again if necessary.

No, when I talk about different currents they are all measured at absorption voltages. I am turning my sterling & victron off and on again to force them into absorption so the voltage goes up to 14.4v and then I can see tail current. When I do this, the tail current appears to be down near the 5A (once it has settled) rather than the 12A from before - ie on resetting the charging, it immediately starts at 20A but then decays to a tail current of 5A. This is similar to what you described. What I dont do is set the alarm for 55 mins ....and often get back too late and it is then in float. That is a good idea.

 

[smileypete]

On 1/18/2018 at 18:09, Dr Bob said:

Thanks Tony. That's what I was thinking. 30A will be fine. I will try this first.

I was thinking this could be an issue with two controllers both fighting each other.

You have both convinced me.

Agree with Tony, 'just do it'. A suitable clamp meter will help tell if the different panels are working equally well or not.

Never heard of MPPTs 'fighting each other', again a clamp meter and voltage readings will help here too. Sounds like one may have been set at too high a voltage, or a battery might have been iffy. ISTR DeanS ran two tracers side by side with no problems.

Edited January 19, 2018 by smileypete

[WotEver]

49 minutes ago, smileypete said:

Never heard of MPPTs 'fighting each other', again a clamp meter and voltage readings will help here too. Sounds like one may have been set at too high a voltage, or a battery might have been iffy. ISTR DeanS ran two tracers side by side with no problems.

I was wondering if one of them had decided it was a good time to run an equalising cycle. It’s about all I can think of other than your suggestion that they were set to different profiles.

It still doesn’t explain ‘boiling the batteries’ though. 

[peterboat]

18 hours ago, WotEver said:

Sounds to me like they need to go back to the drawing board with those then and pull them from sale. 

Seeing as you don’t like blogs, here’s Morningstar’s observations:

https://www.morningstarcorp.com/parallel-charging-using-multiple-controllers-separate-pv-arrays/

Designed to operate in parallel I think is the the bit I noticed and why would I want the tracers back? the two people using them have no issues as I suspect they arnt designed to operate in Parallel which is why I had the problems that I did.

My Midnite is designed to operate in parallel it has a coms lead to make sure it delivers the best controlled charge, [remember these chargers also have a auto desulphation] what would happen if one or both both decided to do it? I dont know but those very clever people that made it do

[smileypete]

22 hours ago, Dr Bob said:

Thanks for that. A fairly simplistic explanation in the video - and assume it is true......but can you help explain what is likely to happen with charge rates as we near fully charged. I dont understand exactly what 'tail' current I should have on my cheapo lead acids to indicate 100% SoC as the current is different from my 3 charging sources ie Victron combi battery charger, sterling atob/alternator and solar.

For reasonably healthy batts I'd look for tail current to fall by less than a third over an hour and use that as a baseline.

This should happen only when tail current is less than one or two percent, depending on batt type and condition.

Also don't forget that using tail current to determine a full charge is only valid when the voltage is at the manufacturers recommended charge voltage, adjusted for temperature.

Edited January 20, 2018 by smileypete

[smileypete]

1 hour ago, peterboat said:

Designed to operate in parallel I think is the the bit I noticed and why would I want the tracers back:? the two people using them have no issues as I suspect they arnt designed to operate in Parallel which is why I had the problems that I did.

Suresure, but without enough detail it's probably best regarded as anecdotal evidence.

I guess the advantage of a comms link is that both controllers can be set simultaneously.

Edited January 20, 2018 by smileypete

[WotEver]

2 hours ago, peterboat said:

Designed to operate in parallel I think is the the bit I noticed..

Well yes, I would expect that to be the bit that you noticed

The only bit of the design that facilitates this, if you read the second half of that sentence, is that the output voltages are strictly controlled - just as they should be with any charge source. 

[Tony Brooks]

The output of the solar controllers would, I hope, be a better DC "wave" form that than from a PCM one and I trust its closer to the DC output of an alternator. Please note that I have not had a scope on the MPPT controller to check but I thought the "magic" happened at a high frequency. There for how does an MPPT controller know the voltage it is looking at is coming from an alternator, battery charger  or another solar controller? If it caused battery boiling indicating an over high charging voltage with another charger why did it not do it with the alternator towards the end of a long day.

This whole thing seems very suspect to me and more likely to be caused by an incorrect setup form the factory. However if the second controller was connected in bright sunshine  and fully charged batteries is it not possible that it set itself to 24 volt, specially if the original one was doing an equalisation charge at the time.

There is something here I simply do not understand. Maybe we will find out what was going on one day.

[WotEver]

4 hours ago, Tony Brooks said:

if the second controller was connected in bright sunshine  and fully charged batteries is it not possible that it set itself to 24 volt, specially if the original one was doing an equalisation charge at the time.

Yup, that’s certainly a possibility. All this gumf about not having them in parallel makes no sense whatsoever. It was either installation error or a faulty unit. 

[Bricksh]

16 minutes ago, WotEver said:

Yup, that’s certainly a possibility. All this gumf about not having them in parallel makes no sense whatsoever. It was either installation error or a faulty unit. 

We have had two tracers running in parallel since April and have had no issues. They are two identical units and I set the settings the same on each. I'm thinking of adding some more panels and a third tracer this year. 

[WotEver]

Just now, Bricksh said:

We have had two tracers running in parallel since April and have had no issues. They are two identical units and I set the settings the same on each. I'm thinking of adding some more panels and a third tracer this year. 

Yup, no reason at all in theory why this shouldn’t work.