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Old 29-08-2016, 07:51   #16
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Re: Battery Voltage in the Morning

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Originally Posted by sailorboy1 View Post
Not a different story, just different wording as I can see how post 1 could be misread.

The 12.6V to me seems to match close enough for me for a 460 AH (rated) battery bank that has 30 AH out (from overnight use), with a 1 amp discharge.

If what the Ah counter was telling you is actually correct then 12.6V with a 1A load is perfectly reasonable... If your batteries were fully charged & rested you should expect to see 12.71V - 12.74V. On a healthy 460Ah bank a 1A load (0.0022C load) should not cause more than a few hundredths of a volt load drop at 100% SOC..
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Old 29-08-2016, 07:55   #17
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Re: Battery Voltage in the Morning

According to what I've learned, your resting voltage after a 30 amp-hr draw down should be around 12.55v. Don't suppose you can cut the draw/input to zero to check?

A 3 amp load is not huge, but is not insignificant either. I would not be perturbed to see 12.5 on the meter (heck, I'd be ecstatic right now ), but 12.4 does seems a bit low.

Oops, I see Mainsail is here. I'll shut up now.
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Old 29-08-2016, 08:19   #18
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Re: Battery Voltage in the Morning

Yes the voltage was exactly what it was. You can trust in that.

If you want to know where the battery is, you want to stop charging and discharging it and then measure the voltage at rest. Give it up to 12 hours rest to be very accurate. BUT I found very accurate results can be had as soon as about 1 hour from disconnect (except after fast charging).

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Old 29-08-2016, 08:20   #19
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Re: Battery Voltage in the Morning

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Originally Posted by Maine Sail View Post
If what the Ah counter was telling you is actually correct then 12.6V with a 1A load is perfectly reasonable... If your batteries were fully charged & rested you should expect to see 12.71V - 12.74V. On a healthy 460Ah bank a 1A load (0.0022C load) should not cause more than a few hundredths of a volt load drop at 100% SOC..
So you don't feel that the solar supplying power into the "system" should affect the battery voltage, since the battery was still discharging?

I don't feel it should and that 12.6V with 30 AH from overnight seems pretty good.
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Old 29-08-2016, 08:22   #20
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Re: Battery Voltage in the Morning

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Give it up to 12 hours rest to be very accurate.
Food in freezer thaws, meat spoils, beer warms up ................................. not happening
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Old 29-08-2016, 08:34   #21
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Re: Battery Voltage in the Morning

Or at least measure the voltage directly at the battery using a trusted volt meter. There are line losses between the battery and the voltage meter if your distance is long and the wires are too small.

Our master lot shunt always reads the actual voltage lower than it should by about .02 volts even though it's connected with 1 gauge wire and it's the first item connected to the battery.



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Old 29-08-2016, 10:45   #22
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Re: Battery Voltage in the Morning

What type of batteries? Can you use a hydrometer on them?
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Old 29-08-2016, 10:57   #23
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Re: Battery Voltage in the Morning

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So you don't feel that the solar supplying power into the "system" should affect the battery voltage, since the battery was still discharging?

I don't feel it should and that 12.6V with 30 AH from overnight seems pretty good.
I don't cause you were using more than what the panels supplied, so the batteries never "saw" the Solar output.
But we are sort of spilling hairs and measuring to the .1 V and counting down to 1 amp. Normally if you want to do that it requires some sophisticated equipment, calibrated to NIST standards, meaning what is sometimes called lab equipment, so there may be some errors just due to the accuracy of the equipment, temperature can affect measuring equipment more than you may realize for example.
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Old 29-08-2016, 11:11   #24
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Re: Battery Voltage in the Morning

I have no real experience with solar but want to learn - isn't the solar panels connected to a charge controller and to the batteries, and not directly to the buss bars supplying current to your onboard loads?

Wouldn't a solar panel increase the voltage to the batteries and raise them up some amount no matter what loads were discharging the batteries at the same time? And - keeping the loads the same on the same battery bank, removing the solar charge source would cause the system voltage to drop by some amount.

or am I way off?
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Old 29-08-2016, 11:11   #25
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Re: Battery Voltage in the Morning

I don't care if it was 12.61, 12.62, 12.6, or 12.58. That would fall into the battery obsessing world

I do care whether the error made it 12.6 instead of 12.45

I was just checking to see if anyone thought I was thinking wrong.
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Old 29-08-2016, 11:28   #26
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Re: Battery Voltage in the Morning

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The other morning my solar panel was supplying about 2 amps into the system, the battery was discharging about 1 amp, the batteries were 30 AH out of a 460 AH bank, the voltage was reading 12.6V.

Can the voltage be believed?
I believe your problem is non-existent. With batteries in a good state of charge and one amp. net input. Battery charging is not linear so you won't see much if any rise in voltage. It will creep up over time.
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Old 29-08-2016, 12:19   #27
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Re: Battery Voltage in the Morning

The solar input is not affecting the battery voltage. Instead how much you draw from the batteries does. IE 3amp load vs 1amp load, thus higher voltage..
If the solar input were greater than the loads then you'd be seeing charging voltage, not battery's..
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Old 29-08-2016, 12:33   #28
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Re: Battery Voltage in the Morning

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The thing is that I've seen the same AH out in the morning with 3 amps discharge before with the solar snoozing, and the voltage reading 12.4-12.5.

So the question is whether the supplied solar is raising the voltage even though it isn't meeting the demand. Or whether an extra couple amps discharge really effect the voltage reading that much (.1-.2).
The answer to your question is YES.

Wit the battery 100%, at rest, you should see a hair over 12.7 Vdc.

with a light load (1 A) and 30 A-hrs, out, will you see a lower voltage (lets say 12.55 Vdc. If you connect the solar charger (or any charging) and it is supply a charge voltage to the battery, the battery voltage will read higher.

When the batteries are deeply discharged, and the solar charger is putting out everything its got, you could easily be reading 12.6 Vdc.

The only way to get an accurate SOC reading is at rest, meaning, no load and no charge voltage. In practice, this isn't realistic on a cruising boat that is actually being used. So you develop a history of what the current voltage reading means, based on load and charge.

When you have a solar charging system, it is good practice to read your battery voltage about an hour after sunset (with all loads turned off). If the voltage is too low (to sustain you through the night) apply an alternate charging source to bring the batteries up (with practice, you will know how long is needed to get enough into them). An hour after you shut off the charging system, recheck the voltage, it will be pretty close to what the batteries are actually at.

In the morning, check the voltage while the sun is still very low. This should be very close to your actual starting voltage. When the sun is high, you won't know what your actual starting voltage is, as you are seeing the solar charge voltage. (Depending on what you have for panels, if you don't have switches to disconnect them or the controller, you can just throw beach towels over them, apply a decent load for 15 minutes, take all loads off for 15 minutes, and take a reading.
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Old 29-08-2016, 12:47   #29
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Re: Battery Voltage in the Morning

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The answer to your question is YES.
you're the only that thinks so, so ........................
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Old 29-08-2016, 13:40   #30
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Re: Battery Voltage in the Morning

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Food in freezer thaws, meat spoils, beer warms up ................................. not happening
So forget about voltage as a measure of anything useful.

For you can apply say a 16 V to a nearly dead battery the add some loads (that freaking fridge if you please) and burpie!!!! you arrive at 12.6 Volt. Ohoooooooo - this battery is GREAT!!!

No, it is not.

You cannot get any info about what the battery is all about if you are charging, it is less accurate while discharging and even less so if you do both at once.

Batteries get measured at rest. Under load only if you know the load exactly. Under load and charge you still could do it but we are getting out of practical.

12.2? Charge it.
14.8? Stop charging.

In between? Use it. And bring it to full charge now and then.

b.
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