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Old 12-11-2018, 12:33 AM   #1
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Voltage to set automatic generator start

I have 4 Interstate GC2 deep cycle for my house batteries. At what voltage should I have my generator start up to charge those batteries?


How long should I charge those batteries?
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Old 12-11-2018, 05:49 AM   #2
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much of this depends on your personal preference, but you can start with a 12.0 Volts setting. As for RUN TIME, it depends on whether you want to ‘fully’ charge the battery bank, or just enough to get you thru several more hours, AND considering what your SHORE setting is at. A lower setting of 15amps will require more run time than if it is set to 30amps. Try 30min RUN TIME and then adjust as needed. : )
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Old 12-11-2018, 08:07 AM   #3
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Voltage is a VERY poor measurement of SOC. There is a correlation between voltage and SOC for a battery that is at room(ish) temperature and has been at rest for at least one hour.

The ONLY proper way to monitor SOC is with a condition monitor that counts amps in and out. Unfortunately the auto generator start does not work off that, even though the information can be available through the remote panel.

So it is a poor solution even though the proper solution is right there.

To answer your question as best as is possible under these less than ideal conditions... At 50% and the conditions described above the standard lead acid battery is at at roughly 12.2V. Taking your batteries below 50% on a regular basis WILL shorten their life. If you have the charger set to maxA it will start at 80A and quickly taper down, so say an average (this is VERY rough math) 50A in the bulk phase. The bank is, say, 400A so to get from 50% to 80% is 120Ah, so at least 2-1/2 hours. Then the amperage quickly goes down in the absorption phase and will take at least another two more to get to 95%. (Very hard to graph that). Then the float is on top of that, but for very little aH gain.

So the answer, sort of, is 12.2V and 3+ hours.

There's a lot of info on batteries here: https://dragonship.blog/battery-monitoring-kit/
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Old 12-11-2018, 08:11 AM   #4
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Quote:
Originally Posted by formerFR View Post
much of this depends on your personal preference, but you can start with a 12.0 Volts setting. As for RUN TIME, it depends on whether you want to ‘fully’ charge the battery bank, or just enough to get you thru several more hours, AND considering what your SHORE setting is at. A lower setting of 15amps will require more run time than if it is set to 30amps. Try 30min RUN TIME and then adjust as needed. : )
Adjust based on what? You're putting (maybe) 35A in a 400Ah bank. That's 10%.... And how are you measuring your results? And how are you staying above 50%? At 12V you are well below. The only way to manage this without a condition monitor is to charge starting at 50% and charge AT LEAST to the end of the bulk phase at which point you'll be ROUGHLY back to 80%. But no way to really tell without standing there looking at the remote.

What you are suggesting will kill that bank in short order. This is not a matter of "personal preference". It's physics.
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Old 12-11-2018, 02:06 PM   #5
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At the nascar races, I set mine to start at 12 volts and run for 2 hours. There is no quiet time at the races so I don't care if it starts in the middle of the night.

I've heard many boon dockers without AGS say that they run for hours in the morning at 4 hours in the evening before quiet time.
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Old 01-22-2019, 01:13 PM   #6
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This is mainly to Oscarvan. I did read you blog regarding the Battery monitoring Kit but have to admit you were above my head a little bit. I would need to study it in detail to really comprehend and plus It would help if I typed it out and not be boondocking in a desert. Until lately my start voltage at 12.2 and run time of 2.5 hours was working fine.
But the last week I've been charging for 2.5 hours and then 2 hour later I was back down to 12.2 and start charging again!!!???? Main electrical usage is Household refrigerator, some overhead LED lights and every now and then a furnace usage.
Yesterday I took the batteries to a RV electrical shop here in Quartzsite, they said batteries were good but I should Equalize them (set absorption time longer) Now I don't see BULK charge, I don' know what I did, but all I see now is Absorption and Float charge.
Any idea how I can get back to having Bulk charge?
Any comments on the Equalization Charge?
And why am I draining my batteries so quickly?
(by the way I have 2 - 120 watt solar panels charging)
Thanks, Ernie
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Old 01-22-2019, 07:32 PM   #7
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You got a lot going on there.....

First off, google "equalization". It is NOT setting the absorption time longer. It is a limited time of HIGH VOLTAGE, to state it simply: "cook" the battery for a short period. It forces sulfate crystals that deposit over time on the plates to go back into solution and frees up the plates to do the chemical thing.

There is no mention of equalization in the Magnum manual. Mine are due, so I'll have to use a clamp on charger capable of that.

As far as why no bulk.... Is the solar panel producing when you look at that? If the charger "sees" the higher voltage from the solar panel it won't see the need for bulk. So, I would take the solar part out of the equation and see what's going on....

Don't know why your batteries are draining so quickly. Either they aren't charging fully to begin with, or something is putting a drain on them (furnace draws quite a bit) or they are not healthy....
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Old 01-22-2019, 08:27 PM   #8
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I think I learned something today! Two weeks ago I was at a friend's place plugged into a 15 amp circuit. I had turned the shore power setting to less than 20 amps. This morning I was reading to get Bulk charge I needed to have a larger Shore Power setting so I changed it to 50 amps. Tonight I now have Bulk Charge! So I have gained a little today.
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Old 01-22-2019, 08:34 PM   #9
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Ah yes, that will do it. Sorry I didn't think of that.
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Old 01-22-2019, 09:03 PM   #10
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I can not believe your blog, it is great! You impress me with your details. Its a great resource!
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