Solar not Working Correctly?

[noelex 77]

Originally Posted by monte

Battery bank is 700Ah lead acid..so 2% is erm ???not sure what the 2% figure relates to?

It is a bit confusing since it is a mixing of terms, (AHrs and A), but the 2% means a current entering the battery of 2x700/100= 14 Amps in your case. The voltage needs to specified as well.

So a your battery accepting 14A, or less at the absorption voltage of say 14.6v or over means it is time to drop down to float. (Others believe 1.5% (10.5A in your case) or 1% (7A in your case) is more appropriate.

[socaldmax]

Originally Posted by simonpickard

Reason I'm getting into this more is that I'm doing the ARC rally soon.

Before I never bothered with my readings overly as every few days we'd head into a marina anyhow and fully charge up. But for the ARC crossing I wanted to know if I could have a net positive at the end of each day.

All I'll be using is autopilot, fridge, instruments and lights. I've measured the cost of each so know my net loss per day. Just need to know how much I can get in on an average day.

Will run some tests and get back to you all.



Please visit my blog:
Sailing-Interlude | Sailing the Med… and beyond

You've gotten a lot of great advice and great background info so far, but maybe we've been looking in the wrong direction. I don't have a BMS, I just look at current and voltage on my solar controller to tell me what is going on at the moment, at dusk I look at voltage under load to determine SOC.


The questions I have for you are:
1. What brand of solar controller is it?

2. What do you have your bulk voltage set at?

3. What do you have your float voltage set at?

4. When you turn on a bunch of loads (like 30A) at midday, what V and A do you see on the controller?

Your float V shouldn't be above your bulk V, but I've seen weirder things.

I didn't see any mention of your wiring gauge. I would check the total length between the panels and controller. Find an ampacity chart and size your cables for 1% total loss or less. Same thing for controller to batteries but keep in mind that section is even lower voltage, so it might need even larger cable for an equal length run. Size matters, as maine sail pointed out.

Whenever I suspect I'm getting shading or the panels are dirty, I simply throw on a big DC load and see what the panels and controller put out. If it seems lower than expected, I'll go up and wash them off or move the rig for less shading (I'm going to move the panels to eliminate that altogether.)

The only time I check SOC is right after dusk. If it looks like there's not enough in there to last the night comfortably, I'll just run the genny for an hour or two. To me, the important issue is harvesting max. power from the panels, and that requires low resistance cabling, no shading and (IMHO) high bulk charging setpoint to keep the controller in bulk mode longer to get a higher SOC.

[socaldmax]

The reason I haven't bought a BMS is so far, it looks like they can be more misleading than accurate unless fiddled with, how long that takes, I don't know.

Since I have constant loads on the battery, whatever current and voltage I see on the controller panel is voltage under load and is pretty easy to get a rough SOC from that. I originally started off with 2 x 155w panels and a 25 A controller feeding 4 x 4 6V GC batteries, for a total of 440AH (220 usable.) After a while, I noticed that I still needed to run the genny at times to help with extra loads (lots of rope lights, TVs, stereos, blenders) so I added another 165w panel and 2 more batteries when I bought new ones.

My point is, instead of trying to wring out every last 1/2 w or cutting back on power consumption, I think it's better to minimize shading, use nice big cables, add panels or batteries to keep up with or exceed your lifestyle (power demands) and suddenly the stress of having enough power disappears.

Nowadays, as cheap as used solar panels are (I recently bought 3300w of panels for my house at 75 cents/watt, these are Sharp panels only 3 yrs old) the only limiting factor is how much room do you have on your boat?

[monte]

Thanks for the explanation noëlex. That explains my question.

[Maine Sail]

Originally Posted by monte

Thanks for the explanation noëlex. That explains my question.

Monte,

The best way to determine this is not necessarily with solar. Fire up the engine when you think it is close to full.

*Is the voltage at the batteries 14.4V +?

*Is the net current the alternator is putting into the batteries less than 1.5% or 2% of 700Ah?

In your case anything less than 14A, but preferably 10A or less at 14.4V, and you bank is cruiser full....

[monte]

Thanks. Simple is good .

[Ex-Calif]

Originally Posted by Maine Sail

Monte,

The best way to determine this is not necessarily with solar. Fire up the engine when you think it is close to full.

*Is the voltage at the batteries 14.4V +?

*Is the net current the alternator is putting into the batteries less than 1.5% or 2% of 700Ah?

In your case anything less than 14A, but preferably 10A or less at 14.4V, and you bank is cruiser full....

Originally Posted by monte

Thanks. Simple is good .

And again I always feel it necessary to "foot-stomp" this part.

That doesn't necessarily mean you have 350 amp hours of capacity available to 50% SOC.

You have to do a controlled discharge test periodically to determine how much capacity has been lost to your bank.

[Stu Jackson]

For the OP:

You could buy a book or two, as suggested.

You could also read these:

Electrical Systems 101

If you do, it'd save Maine Sail and a lot of the rest of us retyping the same stuff over and over again.

Research and homework. sailinglegend is right. See #30 on page 2.

Good luck.

Read the Gotcha article, too. Will help you understand how to work your coulomb counter.

[roetter]

Originally Posted by monte

Thanks Maine sail, great info as always. My monitor is showing
Attachment 87607
So I guess it is close to full...? I'll keep an eye on the voltage in futures..

No! Your batteries are NOT full. The battery monitor is showing 14.28V. If you have lead acid batteries then you need to see these number:

1. 14.4V+ on the battery monitor. I hope you have your solar controller programmed for 14.4V minimum for absorption. Some are programmed out of the box way too conservative.
2. Then (while constantly showing 14.4V+ at the battery monitor) you need to see the amps into the battery go down below 2% of your battery's capacity. For a 400Ah battery that would be less than 8A.

Only those two number together will be 100% full in cruiser's terms. I had to tweak my Victron battery monitor to not sync to full way before the solar had a chance to fill it up. I forget the numbers but is was somewhere around 14.1V and less than 2% amps. All summer long my 950W solar had been filling my batteries to 100%. Then in fall it still showed 100%, but I got low voltage errors even with moderate draws. I hooked up a friends generator and saw over 100A go in, and not even at 14.5V yet. So I was lied to all the time.

Back to your picture: At th point (14.28V and 4A) the solar controller does not have enough intput to push the voltage up to 14.4V+. For that reason you are seeing the low amps. If there was more sun input you would see 14.4V+ but also much higher amps, probably around 25A. Over time if there is enough sun left in the day, the voltage will rise to 14.4V+ if your contoller is programmed properly.

Right now one can only speculate that your batteries are likely about 90% full. But even that can be misleading, because you may have 400Ah installed but they are so badly sulphated that in reality you only have 200AH capacity available.

[roetter]

Originally Posted by simonpickard

Reason I'm getting into this more is that I'm doing the ARC rally soon.

Before I never bothered with my readings overly as every few days we'd head into a marina anyhow and fully charge up. But for the ARC crossing I wanted to know if I could have a net positive at the end of each day.

All I'll be using is autopilot, fridge, instruments and lights. I've measured the cost of each so know my net loss per day. Just need to know how much I can get in on an average day.
....

For the ARC crossing you need to have a bomb proof charging system. Friends of ours lost their generator on day 2, on day 4 the alternotor kicked the bucket. The solar was inoperational from the start and way too small. They went blackship on day 5. Did I say the they had electric heads. With large waves, two people on a rolling mono, with a bucket for their business, and next to no sleep - not fun.

On our crossing I had a wave kill my back up Honda genrator that was running on deck, so now I had to start one engine every 4 hours for two hours during the night. During the day 950W of solar kept up with the demand and gave us enough until about midnight. Many days were cloudy.

Our main consumers - 2 fridges, 1 freezer, autopilot, 2 chart plotters, instruments.

The days are only getting shorter from now on. You are crossing near the shortest day light time of the year. If your solar does not easily provide what you need now then you need more solar. 300W is not a lot, and only getting 100W peak now looks more like 60W peak during the crossing, and that only for 3-4 hours with tapers at both ends.

You should do some crossings now that are 36 hours or more with two nights to check what you get. You still have time to upgrade the system.

Every year there are a few blackships in the ARC.

[Adrian Wood]

In my experience the most important issue if you have multiply panels connected is Blocking Diodes. These are not the ones within the panel itself but external diodes fitted to each +ve side of the panels. I have modified many cruisers' installations' usually with amazing results. Just find as many 40Amp diodes as you have panels and connect them between the panel and the +ve out wire. MAKE SURE THEY ARE THE CORRECT WAY ROUND. This stops one panel trying to back feed into the other panels, especially if one is slightly shaded, or even salt or dust covered and not producing the same voltage as the others.

[noelex 77]

Originally Posted by Adrian Wood

This stops one panel trying to back feed into the other panels, especially if one is slightly shaded, or even salt or dust covered and not producing the same voltage as the others.

Welcome to the forum Adrian, but I have to disagree with you on this one.

I presume you are talking about parallel connection of the solar panels. Shaded solar cells provide very high resistance. You can directly connect a completely covered solar panel to a battery and barely measure the current drain. The same is true of another solar panel they are both simply voltage sources.

Diodes in this application will have a reasonable loss (for a standard diode it is in the order of 0.5v). The loss is going to be greater than the gain.

For solar panels in series an extra bypass diode for each panel is good idea, but this is a very different application.

[monte]

Originally Posted by roetter

No! Your batteries are NOT full. The battery monitor is showing 14.28V. If you have lead acid batteries then you need to see these number:

1. 14.4V+ on the battery monitor. I hope you have your solar controller programmed for 14.4V minimum for absorption. Some are programmed out of the box way too conservative.
2. Then (while constantly showing 14.4V+ at the battery monitor) you need to see the amps into the battery go down below 2% of your battery's capacity. For a 400Ah battery that would be less than 8A.

Only those two number together will be 100% full in cruiser's terms. I had to tweak my Victron battery monitor to not sync to full way before the solar had a chance to fill it up. I forget the numbers but is was somewhere around 14.1V and less than 2% amps. All summer long my 950W solar had been filling my batteries to 100%. Then in fall it still showed 100%, but I got low voltage errors even with moderate draws. I hooked up a friends generator and saw over 100A go in, and not even at 14.5V yet. So I was lied to all the time.

Back to your picture: At th point (14.28V and 4A) the solar controller does not have enough intput to push the voltage up to 14.4V+. For that reason you are seeing the low amps. If there was more sun input you would see 14.4V+ but also much higher amps, probably around 25A. Over time if there is enough sun left in the day, the voltage will rise to 14.4V+ if your contoller is programmed properly.

Right now one can only speculate that your batteries are likely about 90% full. But even that can be misleading, because you may have 400Ah installed but they are so badly sulphated that in reality you only have 200AH capacity available.

Thanks again Rolf. I just checked the Victron Bluesolar 85 solar controller is set for absorption 14.4V max 8 hrs, float 13.8. The Mastervolt Easy battery monitor has the same settings and 2% for the battery full reset figure.
Our battery capacity is actually 840Ah so 2% would be 16.8A

Thanks again, learning a lot! Im surprised your solar didnt keep up crossing the Atlantic. What was your battery capacity for that crossing?

[simonpickard]

Thanks for all the info here everyone. Lots to read through which I will.

My controller is a victron mppt 75 | 50
Not sure what it's set to as I didn't install it but will check. Will also check out the wire gauge.

Need to run a load more tests but here in Spain on a hot day today with no shading on the panels at 11am I'm seeing 7amps in. However the battery monitor is saying I'm at 13.1v so I'm not sure if that's due to me not running the batteries down enough. The battery monitor is saying soc is 100% but the solar controller is in bulk.

Need to read up more of course but wanted to post these..

Great advice about the ARC also. This is the main reason I'm trying to get this sorted now.



Please visit my blog:
www.sailing-interlude.com

[noelex 77]

Originally Posted by monte

Thanks again Rolf. I just checked the Victron Bluesolar 85 solar controller is set for absorption 14.4V max 8 hrs, float 13.8.

8 hours is a very long absorption time. 1-3 hours in the norm.

The absorption time should ideally end when the absorption voltage is maintained and the battery is accepting 2% (I actually prefer 1.5%). Monitor a few typical cycles and see how long this takes to occur.
It will be a little bit variable and with flooded batteries it does not hurt to make it on the longer side of average, but 8 hours is very long.

My system is set up to do this on every cycle, which is better than better than just using an average, but such prescion is overkill especially for flooded batteries. Most systems will not do this, but my last 10 absorption times have been:
37,35,40,24,52,34,6, 21,50,22 mins. (It is set for >5mins at 0.1v below the absorption voltage and 1.5%). If I had a fixed absorption time an hour it would be plenty.

Someone's else usage will be different, which is why the absorption time is variable.

Undercharging kills far more batteries than overcharging, but this idea can be taken too far.

On the other hand your voltage is a bit low for flooded batteries, did you get this from the battery manufacturer?