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Old 11-10-2018, 12:15 PM   #15
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Hi

One further hint if you are charging batteries from a generator - it takes a lot longer than you might think. Four hours of run time per day is a pretty good guess at the minimum time to keep things up to "full". Two hours in the morning and two hours in the evening is about as close as you want to cut it.

Bob


Iíve always used the 50-90% concept when boondocking for a few days. It should only take a couple hours to get from 50 to 90 with an appropriate sized charger but that last 10% can take an additional couple hours since the resistance is so high. I usually sacrifice that 10% and save it for when I get back to shore power and can charge over night. That keeps my gen run time to ~ 2 hours per day.
Solar certainly does help.
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Old 11-10-2018, 01:08 PM   #16
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Iím wonderingóis it possible to charge the batteries from solar and the generator at the same time or is it one or the other?
Hi

Simple answer - it will be one or the other. In most cases, that will mean it all comes from the converter / charger. That's not all bad. Your converter / charger should put out 30 to 50A into the batteries. The 5A or so that an 80W panel will deliver is pretty much nothing by comparison.

Charging lead acid's is not all about peak current. It takes a *long* time to get from 80% charged to >=100% (yes batteries can go past 100% rated charge level). Since you stop using at 50%, the difference between 80% and 100% is almost twice the usable battery.

Bob
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Old 11-10-2018, 01:49 PM   #17
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Ok that’s what I figured. Thanks, uncle bob.
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Old 11-10-2018, 02:35 PM   #18
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Nryn,
When we test this in the shop, it is usually the converter however not always. When the battery bank is large enough to accept the full rated output of the converter, say 60 amps, and an additional charge source is added, the current will increase to the point where the battery internal resistance will not accept any more. Might only be a few more amps or maybe more but it will begin to taper rather quick as the resistance builds.
A lot of toy haulers and motor homes delivered over the years with huge battery banks have 2 converters wired in parallel to handle the duty of a large bank plus the normal loads of the accessories.
As Iím sure you know itís a shared load. If you have a 55 amp converter like Airstream uses and are consuming 10 amps for lighting etc, you have derated your charger to 45 amps.
That said in your typical configuration in an Airstream with a pair of interstate group 24s I would be surprised if you ever saw more than 40-45 amps delivered to those batteries say 50% discharged but maybe. It would be brief if you did and would begin to taper.
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Old 11-10-2018, 06:06 PM   #19
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"It should only take a couple hours to get from 50 to 90 with an appropriate sized charger but that last 10% can take an additional couple hours since the resistance is so high."

This is one way in which lithium batteries have a big advantage: they can bulk-charge at full speed right up until they're full. That long absorb period that all lead-acid batteries suffer through, during which juice is being fed to the battery more and more slowly, is all but eliminated.

I'm not saying everybody needs lithium. They're expensive as heck, and they have some drawbacks of their own. But when it comes to charging, they're a lot faster, because the time-consuming absorb phase is not necessary.
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Old 11-10-2018, 06:36 PM   #20
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"It should only take a couple hours to get from 50 to 90 with an appropriate sized charger but that last 10% can take an additional couple hours since the resistance is so high."

This is one way in which lithium batteries have a big advantage: they can bulk-charge at full speed right up until they're full. That long absorb period that all lead-acid batteries suffer through, during which juice is being fed to the battery more and more slowly, is all but eliminated.

I'm not saying everybody needs lithium. They're expensive as heck, and they have some drawbacks of their own. But when it comes to charging, they're a lot faster, because the time-consuming absorb phase is not necessary.
I totally agree with that Paprika. We are all students of the benefits of each now as we were when AGM came out. Getting easier for those that spend a lot of time boondocking to justify upfront cost.
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Old 11-11-2018, 09:06 AM   #21
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Hi

Ummm ..... errrr ..... yes this *is* being picky. Sorry about that

In electronics / electricity resistance is something that obeys ohms law. A lot of what goes on in a battery is not strictly speaking a resistance ... (yes there are a few things that are).

Why does that matter? Well if it's just an ohms law thing then all you need to do is ramp up the voltage some more. That's not what works with batteries because not all of what's going on is an ohmic ( = a resistance) sort of thing.

Bob
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Old 11-14-2018, 11:44 AM   #22
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Mains battery charger supplied from a generator AND solar chargets will coexist without significant issues. Depending on the state of the batteries either one. or both charging systems will show current being supplied.
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