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Old 24-05-2013, 06:59   #1
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battery charging from my generator

I have a question about charging my house Bank ,which consist of 5. 8d batteries .I'm currently in the morning field so must charge via the generator . my charger is a magnum inverter charger ,with 100 amp charger .



so here is the scenario .......with such a large house Bank my voltage never drops below 12 . 4. when I get up in the morning I start the gen set. the Magnum shows bulk charging at 107 amps. after less than an hour this goes into absorption mode . still over 1 00 amps .the charging rate seems to drop in a reasonable amount of time . accepting that I will never run the gen set long enough to go into float charging stage , at what charging rate should I turn off the generator ? In other words at what charging amps displayed on my panel should I call it a day for.charging, and shut down the generator ?o
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Old 24-05-2013, 07:12   #2
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Re: battery charging from my generator

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Originally Posted by motion30 View Post
I have a question about charging my house Bank ,which consist of 5. 8d batteries .I'm currently in the morning field so must charge via the generator . my charger is a magnum inverter charger ,with 100 amp charger .



so here is the scenario .......with such a large house Bank my voltage never drops below 12 . 4. when I get up in the morning I start the gen set. the Magnum shows bulk charging at 107 amps. after less than an hour this goes into absorption mode . still over 1 00 amps .the charging rate seems to drop in a reasonable amount of time . accepting that I will never run the gen set long enough to go into float charging stage , at what charging rate should I turn off the generator ? In other words at what charging amps displayed on my panel should I call it a day for.charging, and shut down the generator ?o
What is "the morning field" ?

Best for the batteries is to keep charging until they have been in float for at least an hour or so. The shorter you charge, the more their lifespan gets reduced. As this is not a workable situation, there are two solutions:

1. replace batteries with a type that don't minds living partially charged (= Lithium, so join the LiFePO4 crowd). This is expensive.

2. Live with it. Buy a battery monitor that shows you State of Charge (SOC) and don't let them go below 50% and stop charging at 80%. Fully charge them once a month, equalize them now and then if the manufacturer recommends that.
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Old 24-05-2013, 07:22   #3
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Re: battery charging from my generator

3. buy a solar panel that can take over after reaching absorption and the charger is starting to lope along below 40A or so.

Mark
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Old 24-05-2013, 07:23   #4
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Re: battery charging from my generator

Jedi. the only way I have to judge. Soc currently is voltage mostly it does not drop below 12 .5 . so I do not think I am discharging my batteries too deeply a battery meter and a larger charger is in my future but it will have to wait till after this cruise my generator has been running just about two hours now this morning. and my panel the showing a charging rate of 36 amps and..that is in an 1100 amp battery bank
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Old 24-05-2013, 07:24   #5
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Re: battery charging from my generator

Your charger isn't set right. 100 amps is too high to enter absorbtion. Try setting it at 50 or 60 amps.
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Old 24-05-2013, 07:26   #6
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Re: battery charging from my generator

Everybody who charges from a genset struggles with balancing a good charge with a reasonable generator run length.

I usually charge mine to 80% to 85% and let them go down to 60% or so, occasionally 50%. Much beyond 80% is just not worth it, as the acceptance rate of the batteries has dropped to almost nothing.

Another way to look at it is what kind of load do you have on the genset. If you have other things to do with AC power (I have a washer/dryer on board, for example), then as long as you've got some load on, there's no harm in running the genset longer. And for sure, don't shut down the genset if you still have a lot of charging current going in -- 15 -- 20 amps, say.

It's not all that good for your batteries, but that's life on a mooring. You can minimize the damage by bringing them up to a really full charge at least once a week or so. For me, that can be provided in different ways -- a night in a marina on shore power, or a longish motor somewhere, or if I really get desperate, I do have a 1kW Honda generator I can run all day long to put a finishing charge on the batteries.

As long as you don't let them go below 50%, and you give them a good, full charge periodically, they will be ok.

One little quibble with Nick's otherwise excellent post -- I wouldn't really on a battery monitor to tell you your SOC, other than as a very rough guess, and even then only if you have carefully calibrated and checked it. These things are notoriously inexact. In my opinion, the best way to know your battery SOC, other than a specific gravity reading (which I also do regularly), is no-load resting voltage reading. Ideally this should be done with 0.0 amps charging or discharging for many hours, but I think you can get a decent picture from the voltage with a very small load relative to bank capacity, with no big loads or big charging currents in the last couple of hours.

That's the best of a bad bargain -- other than SG, there really isn't an exact way to measure SOC, in my opinion.
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Old 24-05-2013, 07:27   #7
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Re: battery charging from my generator

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Originally Posted by colemj View Post
3. buy a solar panel that can take over after reaching absorption and the charger is starting to lope along below 40A or so.

Mark
Indeed. If you have space for it.

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Old 24-05-2013, 07:30   #8
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Re: battery charging from my generator

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Your charger isn't set right. 100 amps is too high to enter absorbtion. Try setting it at 50 or 60 amps.
The battery determines that not the charger, you dont set absorption mode current, The charge acceptance of teh battery does that,.

And yes, the transistion from bulk to absorption is not abrupt so you could easily enter "absorption" at close to bulk currents.

OP I say , if you have no other method of charging, then you need to bring the bank to 100% or as close as possible certainly every couple of days or so, to avoid damaging the batteries. Hence once a week try and run the charger until you get to <10 A. otherwise I agree with others , stop around 20-30A

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Old 24-05-2013, 07:31   #9
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Re: battery charging from my generator

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Originally Posted by motion30 View Post
Jedi. the only way I have to judge. Soc currently is voltage mostly it does not drop below 12 .5 . so I do not think I am discharging my batteries too deeply a battery meter and a larger charger is in my future but it will have to wait till after this cruise my generator has been running just about two hours now this morning. and my panel the showing a charging rate of 36 amps .
12.5 volts open circuit is 80%, more or less. If you have had a small load (relative to bank capacity) on, then this test will somewhat understate the state of charge. If the batts have been recently charged, then this test tells you nothing, because you will have a surface charge.

I bet your volt meter is not very accurate and is overstating the voltage. If your batts are still taking 36 amps, then you will not have reached 80% charge, I don't think.
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Old 24-05-2013, 07:40   #10
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Re: battery charging from my generator

We use Our Victron Battery Monitor to determine how long we run the generator. Once the number of AH used over night reaches 0 and the SOC is showing 100%, they reach both at about the same time, we shut it down. This battery bank is going on 5 years without showing any signs of problems. We do try and equalize the house bank once a month. The start battery is charged via an echo charger that runs off the house bank. Chuck
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Old 24-05-2013, 07:47   #11
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Re: battery charging from my generator

The change from bulk phase to absorption phase is based on voltage, not current. The internal resistance of the batteries, together with the charger limits, is what determines the current.

If you have no battery monitor then buy a decent multimeter to measure battery voltage, or to calibrate/confirm your volt meter on your panel. I agree with others that your readings are suspect.

So, compared to what you do now, the only thing to change is to charge the batteries all the way now and then. Once a week is better than once a month but once a day is better still so you have to find that line between what is best and what you can keep up with. I tend to abuse my batteries a bit but they (Trojan L16's) take it with pride and last 6+ years with ease.
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Old 24-05-2013, 07:49   #12
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Re: battery charging from my generator

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Originally Posted by Waterwayguy View Post
We use Our Victron Battery Monitor to determine how long we run the generator. Once the number of AH used over night reaches 0 and the SOC is showing 100%, they reach both at about the same time, we shut it down. This battery bank is going on 5 years without showing any signs of problems. We do try and equalize the house bank once a month. The start battery is charged via an echo charger that runs off the house bank. Chuck
Keep in mind that unless your battery monitor is very fine tuned in three respects -- (a) properly zeroed recently at a true full charge; (b) adjusted for changing real battery capacity; (c) properly tuned for the real Peukert coefficient of your actual battery bank, which changes over time -- these numbers will be off -- that is, the number which says you have put all the power back into the batteries, and the number which says you are at 100% (and they're both derived from the same calculation, so they are not checks of each other).

If you are really getting them to 100% before shutting down your genset, then you are running for hours with a very small load -- good for the batts, but not so good for the genset (or your own peace and quiet). It takes a long, long time to get from 80% to 100% (unless you have LiFePo batts, of course ).
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Old 24-05-2013, 07:50   #13
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Re: battery charging from my generator

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12.5 volts open circuit is 80%, more or less. If you have had a small load (relative to bank capacity) on, then this test will somewhat understate the state of charge. If the batts have been recently charged, then this test tells you nothing, because you will have a surface charge.

I bet your volt meter is not very accurate and is overstating the voltage. If your batts are still taking 36 amps, then you will not have reached 80% charge, I don't think.
The 12.5 volt reading is.20.hrs or so after running the charger so no surface charge issue. the battery bank is over 1100 amps and I really do not consume much power other than refrigeration solar panels are definitely in my future . I will check the accuracy of the voltage reading on my panel with a multimeter and my hydrometer later this evening
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Old 24-05-2013, 07:56   #14
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Re: battery charging from my generator

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The 12.5 volt reading is.20.hrs or so after running the charger so no surface charge issue. the battery bank is over 1100 amps and I really do not consume much power other than refrigeration solar panels are definitely in my future . I will check the accuracy of the voltage reading on my panel with a multimeter and my hydrometer later this evening
There's nothing wrong with using voltage to judge SOC -- that's what I rely on more than anything, although I have a Victron battery monitor.

If you check the accuracy of your voltage meter and then check that against specific gravity of your batts, you should be good to go

You have a bit larger bank than I do (I have 420 amps at 24v), but my refrigeration will eat it up pretty well in 24 hours. It is true that I have two separate reefer units, one deep freezer and one fridge (don't know what you have). Even if I'm not using power for anything but lighting, phone & laptop charging, and refrigeration, my batts will still get down to 60% -- 65% in 24 hours, even from a 100% charge.

As others have said, solar is the killer app for this issue if you have space for it. Nothing will do that finishing charge from 80% to 100% like solar.
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Old 24-05-2013, 08:12   #15
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Re: battery charging from my generator

You. guys make me climb in my building so early in the day . my multimeter which I've always considered reliable, shows my charger voltage at 14. 37 the Magnum panel shows the voltage bouncing between 14.3 and 14.4 this would indicate the control panel seems relatively accurate
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