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Old 17-06-2012, 04:45   #1
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Float voltage too high?

I've just finished installing my solar panels, 4x80w with a mppt regulator, now the regulator charges pretty much all it can give till the bank reaches 14.4v , it then throttles back to 14.2v for a while, then drops to 13.8v , it is supposed to float at 13.4v which it does if i turn everything off, so there is no load on the batteries.

The problem is, living aboard I have the fridge on constant and various other loads , the regulator is rarely dropping down to 13.4v and staying mostly at 13.8v, this is kinda high for the agm batteries which say a float from 13.2 to 13.6 , I am wondering if it will do them any long term harm?

Granted I will shortly be back out on the open water, so will be using much of the excess power to run the water maker and ice maker for a while each day, which should certainly reduce the time the batteries are spent at full charge.

For those that are interested, the mppt is giving about 5-10% more amps than the panels are producing, So if you are maxed out on space for solar panels, I'd say they are well worth looking into. It even ups the voltage for when the panels voltage is lower than the batteries voltage, ok only worth a few watts at the start and end of the day, but every little helps!
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Old 17-06-2012, 05:54   #2
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Re: Float voltage too high?

It sounds like it is not really making it to float, or that it is not staying in the absorption stage long enough to fulfill its programed scheme. When this happens, do you know for sure that your batteries are fully charged?

If you are drawing current, then your batteries will not go to float unless the charging source can make up for the draw. If your observations are happening late in the day, it is possible that the solar cannot compensate for this.

I wouldn't worry about the higher voltage on the AGMs - I doubt the batteries are seeing it as a static, equilibrium voltage and I doubt it stays at that voltage long enough to matter.

We have 480W of solar through a MPPT and never see the batteries reach float off of it. Several hours in absorption is a good day for our batteries.

If your panels are not shaded much, try hooking them up in 2 parallel sets of series - you will probably get another 10%. If they have no shading issues at all, try hooking all four in series.

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Old 17-06-2012, 06:47   #3
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Re: Float voltage too high?

Before hooking 4 panels in series which means an open circuit voltage of about 70 v, make sure that your controller can handle that voltage. Most can't. Also 70 V is getting to the dangerous level and I suspect that the electrical code requires an entirely different wiring approach for that voltage.

David
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Old 17-06-2012, 07:11   #4
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Re: Float voltage too high?

The float voltage should be same irrespective of the load. It may be temperature compensated and it is very cold this will raise the float voltage, but it should still be same with and without load.

Most regulators operate on 2 voltages bulk /absorption (which are the same voltage point) and float which is lower.
Some regulators can be set with a separate bulk and absorption voltage ( giving 3 voltage points)
In adittion most can be set for an occasional equalisation voltage.

The 4 different regulation set points you are experiencing (14.4, 14.2, 13.8 and 13.4) presumably with excess solar power are unusual and not how the charging algorithm normally works.

Very few regulators can boost voltage

Be a bit suspicious of the regulators display reading they often exaggerate the boost MPPT is providing.

What brand and model is the regulator?
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Old 17-06-2012, 08:17   #5
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Re: Float voltage too high?

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Originally Posted by djmarchand View Post
Before hooking 4 panels in series which means an open circuit voltage of about 70 v, make sure that your controller can handle that voltage. Most can't. Also 70 V is getting to the dangerous level and I suspect that the electrical code requires an entirely different wiring approach for that voltage.

David
Excellent point, I should not have given that advice without mentioning this.

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Old 17-06-2012, 08:27   #6
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Re: Float voltage too high?

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Originally Posted by noelex 77 View Post
The float voltage should be same irrespective of the load. It may be temperature compensated and it is very cold this will raise the float voltage, but it should still be same with and without load.

Most regulators operate on 2 voltages bulk /absorption (which are the same voltage point) and float which is lower.
Some regulators can be set with a separate bulk and absorption voltage ( giving 3 voltage points)
In adittion most can be set for an occasional equalisation voltage.

The 4 different regulation set points you are experiencing (14.4, 14.2, 13.8 and 13.4) presumably with excess solar power are unusual and not how the charging algorithm normally works.

Very few regulators can boost voltage

Be a bit suspicious of the regulators display reading they often exaggerate the boost MPPT is providing.

What brand and model is the regulator?
I agree, but I suspect he is never really getting to float mode.

Fluctuations due to loads are normal. We will often be at, say, 14.2V on our way to absorption when the fridge kicks on and we then go down to 13.6V, but the solar controller is still running its charging regime as normal. Normal cyclical loads will effect the battery voltage you see during the day - which is not indicative of the charging regime of the solar controller.

Most charging regimes are programmed to spend several hours in absorption, so getting to float on solar is uncommon in most cruising boats.

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Old 17-06-2012, 08:51   #7
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Re: Float voltage too high?

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Originally Posted by colemj View Post
Most charging regimes are programmed to spend several hours in absorption, so getting to float on solar is uncommon in most cruising boats.

Mark
No problem here in the sunny Med.
4 hours 47 min on float today and there is still 3 hours of daylight to go.
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Old 17-06-2012, 11:02   #8
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Re: Float voltage too high?

Bear in mind I'm sitting in a marina just now, so the batteries started off well topped up,as best as i can see, it runs to 14.4.v max then backs down to 14.2v with 10a max, then drops to 13.8v is i unload things it drops to 13.4 i imagine that must be the float phase, its just as soon as i put anything on its jumps back to 13.8 and a few amps, the amps kinda appear related in a way to my use, eg if drawing 4 amps it puts in 6 if drawing six it puts in 8.

Its a german unit, Solar Fernbedienung IVT is the company name, looks kinda like higher end chinese stuff with a bit of thought put into it, Have measured current in/out of the panels, the logger is correct it is gaining anywhere from 0.5 to 2 amps extra over the panel output.

Colemj , you must be one power hungry boat with that much and never reaching float
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Old 17-06-2012, 12:09   #9
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Re: Float voltage too high?

There was a thread a few months ago about IVT regulators.
They seem to use a very unusual charging procedure.


MTTP Solar Charge Controllers

The important question is will the charging algorithium hurt the batteries. I doubt it but
What type of AGM batteries are they?
How long do spend at 14.2 or 14.4v?
What current is going into the battery at the various voltages?
What temperatures?
Have you checked the voltages at the battery?
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Old 17-06-2012, 12:26   #10
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Re: Float voltage too high?

Thanks for the pointer, read the thread, they appear to work quite well, looks like a kind of fuzzy logic, no preset routine, once it gets to around 14+ volt mark, it kinda hops forward and back, from up to 14.4v then back down to 13.8, with all load off it drops to 13.4 and does the pulse desulphation thing, until you load the batteries and away it goes again.

it must sense the voltage drop under load, then apply enough current to bring the voltage back up to 13.8v, ie trying to compensate for any load you put on the system, fairly clever in some respects.

Checked all currents and voltages at the panels/battery and they all match, def 5-10% boost over the standard regulators. all in all it was about 200 UK pounds with the display /data logger, pretty good value all in all.
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Old 18-06-2012, 06:11   #11
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Re: Float voltage too high?

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Originally Posted by stevensuf View Post
Colemj , you must be one power hungry boat with that much and never reaching float
Well, it's all relative. We know boats that use less than us and boats that use more. We seem to be about average with all the boats we meet. We use ~150Ahr/day - a bit more when we run the watermaker a long time and a bit less when we don't use our computers much. Surprisingly, our fridge is third down on the list for power after those two!

So, here in Panama with 480W of solar through a MPPT controller, we see 120-170Ahr output/day from solar. The daylight is always ~12hrs here due to latitude and the heat is tremendous, which cuts the output of the panels. When we lived in CT, USA, where it is cooler and the summer days are longer, we had no problem getting 200+Ahr out of them.

So on a sunny day here, the panels mostly take care of our daily usage when we don't run the watermaker much, but never provide enough to put the batteries into float mode. We are happy spending an hour or so in absorption and bringing the batteries up to a full charge once a week or so by bringing them up to absorption in the morning with the generator and letting the solar take it from there.

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Old 18-06-2012, 06:13   #12
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Re: Float voltage too high?

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Originally Posted by noelex 77 View Post
No problem here in the sunny Med.
4 hours 47 min on float today and there is still 3 hours of daylight to go.
In Panama, we get 12hrs between sunrise and sunset. Your time spent in float is almost our entire solar-usable daylight!

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Old 18-06-2012, 06:32   #13
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Re: Float voltage too high?

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In Panama, we get 12hrs between sunrise and sunset. Your time spent in float is almost our entire solar-usable daylight!

Mark
15 hours between sunrise and sunset today.
Sunset is not till 9 pm.
The only drawback is sunset drinks need to be started early. Crusing involves some sacrifices
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Old 18-06-2012, 06:36   #14
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Quote:
Originally Posted by stevensuf
Thanks for the pointer, read the thread, they appear to work quite well, looks like a kind of fuzzy logic, no preset routine, once it gets to around 14+ volt mark, it kinda hops forward and back, from up to 14.4v then back down to 13.8, with all load off it drops to 13.4 and does the pulse desulphation thing, until you load the batteries and away it goes again.

it must sense the voltage drop under load, then apply enough current to bring the voltage back up to 13.8v, ie trying to compensate for any load you put on the system, fairly clever in some respects.

Checked all currents and voltages at the panels/battery and they all match, def 5-10% boost over the standard regulators. all in all it was about 200 UK pounds with the display /data logger, pretty good value all in all.
This sounds normal to me. Regulators doing a good job!
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Old 18-06-2012, 07:05   #15
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Re: Float voltage too high?

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This sounds normal to me. Regulators doing a good job!
It's not how most regulators behave. Some of the behaviour like increasing the float voltage when a load is applied is very atypical.
It is difficult to come to conclusions without seeing it in action. I don't think it's doing any great harm, but it's probably not charging the batteries as quickly as they could be, so in many situations the algorithm will reduce the solar panel output.
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