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Old 03-03-2011, 11:27   #106
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Re: Solar Power

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One needs both a solar charge controller AND a battery monitor. The batteries will self discharge and without the Link 10, (or similar) counting the amps in and amps out of the batteries, you never really know where your battery's charge is. M.

???

Why not just have a look at the voltage?

I would guess that when a battery is neither charged nor discharged and has been sitting like this for a moment, the voltage corresponds to the state of charge.

b.
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Old 04-03-2011, 09:47   #107
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Re: Solar Power

watts X .3 is my average output in the Caribbean. So, 130W panel X .3 and I expect to average = 39amps average/day. Subject to battery discharge state, clouds and other shading of panel, your latitude, etc.. Your mileage may vary.
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Old 04-03-2011, 10:13   #108
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Re: Solar Power

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Originally Posted by barnakiel View Post
???

Why not just have a look at the voltage?

I would guess that when a battery is neither charged nor discharged and has been sitting like this for a moment, the voltage corresponds to the state of charge.

b.
In the old days, we did go by v, for lack of a better system. In fact, reading the specific gravity of a wet battery, (each cells averaged out #) was a rather accurate way, but WAY too much hassle!

Voltage is EXTREMELY inaccurate as far as knowing a batteries state of charge. If no juice went in or out for half a day, then a v reading of 12.6 is a full "wet" battery. The thing is, that this RESTED BATTERY is hard to do, while living on the boat, and a v of 12.4 is quite low. The sensor line losses, and analog meeter's inaccuracies, make this useful only to know if the battery has some charge or not. It won't tell much more.

The "Link 10" and their cousins, have a shunt in the NEG house bank wire. Attached to the shunt, (and + side), are sensor wires that run to the Link 10s little computer brain. Once you teach the computer the batteries capacity and type, then top off the battery, it counts the amps going in or out with astounding accuracy, to the tenth of an amp! It re-zeros itself every day after topping off the battery bank to 100%. They're the cats meow!

Mark
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Old 04-03-2011, 15:15   #109
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Re: Solar Power

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Originally Posted by Mark Johnson View Post
The "Link 10" and their cousins, have a shunt in the NEG house bank wire. Attached to the shunt, (and + side), are sensor wires that run to the Link 10s little computer brain. Once you teach the computer the batteries capacity and type, then top off the battery, it counts the amps going in or out with astounding accuracy, to the tenth of an amp! It re-zeros itself every day after topping off the battery bank to 100%. They're the cats meow!

Mark
FWIW, there is a difference between precision and accuracy. Just because the monitor says there is 70.6% remaining doesn't make it true. The reset at "100% charge" is a kludge that covers-up errors. IME, the errors tend not to be canceling and accumulate between resets. It is certainly nice to have a charge computer particularly if it does other stuff like controlling alternators. However, I find I quite regularly check my computer against voltage drop / rise v net amps to check the state of charge which is less precise but sometimes more accurate than what the monitor says. Charge monitors have measurement errors and use simplified models to assess the state of charge. IMO, it is important to understand that just because they show a given number of significant digits is no reason to believe that they have reliable accuracy to that number of digits. Evidence suggests that they do not. Keeping an eye on voltage and amps can reveal when the controller is mis-representing the SOC and also help track the health of the bank. It may be old fashioned but it is still a good and useful habit.

Tom.
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