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Old 05-09-2024, 08:07 AM   #1
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Easiest way to charge batteries with a Generator...

I'm new to using a generator to recharge the batteries in our 2010 International 27FB. Original converter, No special batteries, Interstate Lead acid.

I have a Champion Dual Fuel 2500 watt inverter generator.

What is the best way to quickly charge the batteries when camped?

Feed power to the onboard converter via the 30amp hookup?

If so, how long would it take to "top off" the batteries?

Or use an automotive type battery charger plugged into the generator?

I assume that I would have to disconnect the batteries to isolate them if charging using the automotive charger.

We have a big trip planned, mostly camping where we would have shore power. A couple of stops we would have maybe 4 days without. Planned on using the generator at those stops to top off the batteries.

No plans to run A/C on generator.
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Old 05-09-2024, 08:29 AM   #2
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Your original converter is probably in the 50 amp range, so it should top off your batteries pretty quickly. An automotive type charger will also work, but I see no need for it. You do not need to isolate you batteries if an automotive charger is used.
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Old 05-09-2024, 11:39 AM   #3
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I charge with the generator just by plugging the trailer into the generator and using the power converter. My guess is that there is no "fast" way to charge lead acid batteries and certainly no fast way to "top them off". The lead acid battery charge rate slows down as the batteries get more charge. The last 15% or so is very slow. Their fast charging rate is a huge advantage for lithium batteries. If using a battery charger directly is faster that is because the battery charger probably works at a higher charge voltage than the converter and that is probably not good for the deep discharge batteries in the trailer. And maybe heigh enough to be bad for some of the electrical systems in the trailer.
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Old 05-09-2024, 01:03 PM   #4
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I have found that it takes about 36 to 48 hours to top off the batteries to 100% when connected to shore power. Use your generator as needed for electrical use when camping as it will help keep the batteries above 80% or so. You might want to consider a portable solar suitcase panel which can charge all day with out the noise.
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Old 05-10-2024, 04:27 PM   #5
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Quote:
Originally Posted by mojo View Post
I have found that it takes about 36 to 48 hours to top off the batteries to 100% when connected to shore power. Use your generator as needed for electrical use when camping as it will help keep the batteries above 80% or so. You might want to consider a portable solar suitcase panel which can charge all day with out the noise.

Good advice, thanks.

Any suggestions for a reasonably price solar suitcase?

https://www.harborfreight.com/100-wa...kit-63585.html

Would something like that work?

Thanks to the others that replied as well.
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Old 05-10-2024, 04:49 PM   #6
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Quote:
Originally Posted by RxGuy View Post
Good advice, thanks.

Any suggestions for a reasonably price solar suitcase?

https://www.harborfreight.com/100-wa...kit-63585.html

Would something like that work?

Thanks to the others that replied as well.
While I have no direct experience with that particular product, I'd keep looking. If you catch a decent sale you can find good 200W portables in the $275 range (sometimes those need a charge controller but those are readily available as well.) You'd want more than a 100W array to be able to recover a decent amount of charge in a day. There are LOTS of brands in the lightweight 200w-400w portable market at the moment, so they have good sales from time to time, and there are several youtubers who do detailed comparisons of them.
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Old 05-11-2024, 09:02 AM   #7
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I have a Renogy 100W suitcase which does a good job but they often run sales and have larger 200w portables. Just get a extra long extension cable so you can move it with the sun angles.
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Old 05-11-2024, 09:18 AM   #8
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We have had our GoPower 80W solar "Renogy 200 Watt 12 Volt Monocrystalline Off Grid Portable Foldable 2Pcs 100W Solar Panel Suitcase Built-in Kickstand with Waterproof 20A Charger Controller" is popular and pretty good price. We store ours on the floor at the end of our twin bed. Comes in handy for extended stays, but we are also using 6V Trojan T105 batteries, which are a bit stronger for boondocking then the 12V Interstates.

One thing about charging your Interstates, AS used to supply 12V Interstates which were experiencing a "lot" of issues. Partly because the older AS, pre-2018, all had single charge mode converters, which would "boil" out the water in the battery if left plugged in to shore power. Many of us, even with new AS's experienced a dead battery shortly after taking purchase and had to get new batteries. Inerstate was pretty good about replacing them free, but still, it was a hassle to remove/replace, when the issue was the converter! AS went away from those converters in 2018 and uses a multi-stage converter now that "knows" the state of your battery and charges accordingly...(my explanation). If you experience issues, if it were me, I would look at replacing the entire system with LI today. When my 6V's go, thats where I am heading for replacement; with a couple solar panels on top.
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Old 05-12-2024, 07:40 AM   #9
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We have had our GoPower 80W solar "Renogy 200 Watt 12 Volt Monocrystalline Off Grid Portable Foldable 2Pcs 100W Solar Panel Suitcase Built-in Kickstand with Waterproof 20A Charger Controller" is popular and pretty good price. We store ours on the floor at the end of our twin bed. Comes in handy for extended stays, but we are also using 6V Trojan T105 batteries, which are a bit stronger for boondocking then the 12V Interstates.

One thing about charging your Interstates, AS used to supply 12V Interstates which were experiencing a "lot" of issues. Partly because the older AS, pre-2018, all had single charge mode converters, which would "boil" out the water in the battery if left plugged in to shore power. Many of us, even with new AS's experienced a dead battery shortly after taking purchase and had to get new batteries. Inerstate was pretty good about replacing them free, but still, it was a hassle to remove/replace, when the issue was the converter! AS went away from those converters in 2018 and uses a multi-stage converter now that "knows" the state of your battery and charges accordingly...(my explanation). If you experience issues, if it were me, I would look at replacing the entire system with LI today. When my 6V's go, thats where I am heading for replacement; with a couple solar panels on top.
That didn't make any sense! Somehow my first response got twisted a bit. I meant to say, we have had our 80W GoPower solar, folding suitcase for several years, and it does fine job of toping off while camping, and stores at foot of my twin bed. The one that I would suggest today, would be the "Renogy 200 Watt 12 Volt Monocrystalline Off Grid Portable Foldable 2Pcs 100W Solar Panel Suitcase Built-in Kickstand with Waterproof 20A Charger Controller"
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Old 05-15-2024, 09:32 AM   #10
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Hi

Lead acid batteries are a bit complicated. Sorry about that.

You run your battery from 50% rated capacity to 100% rated capacity. Go below 50% and you wear them out quickly. This is the magic "don't go below 12.0V" rule.

Charging them to 80% rated capacity usually goes pretty quick (yes it could be 70% on some batteries ...). More or less, that's "half full" as far as what you will use from your battery. A "50A" converter charger likely puts in 30A max when doing this. When new your pair of batteries came in at 140 to 200 AH total rated. At 30A, you would get to "half full" in about 2 hours.

Getting the rest of the way is the "yikes !!!" part of this. The battery does not accept "full current" once it gets to that "80%" point. It no longer matters how big your charger is. It might take 6 hours, it might take a lot longer to get to 95%. That last 5% ... who knows ...

Solar is fine and it will charge the batteries. You want a setup with a *good* controller on it. Cooking your batteries with the solar gizmo ... not a great idea. Figure that a 100W solar will typically give you 50 to 60W. That's about 4A into the battery. If it does this for 5 hours a day, you get 20 AH of charge.

Next up, lead acids (like all batteries) wear out. How fast they wear out depends on a lot of things. What does "wear out" mean? The manufacturer defines it as only providing 80% of rated capacity when fully charged. Some RV folks define it much more loosely. Doing a proper capacity test on your batteries is *not* something we tend to do (yes, that includes me ).

For most, 4 years is "pretty long" when using typical flooded lead acid batteries. If you are after that "80%" capacity, it's a pretty reasonable point to start shopping. Yes, this assumes you depend on batteries to keep things going. Not everybody does ....

Fun

Bob
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Old 05-15-2024, 09:52 AM   #11
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Here is a helpful blog article on the Airstream Club site about this.

https://blog.airstreamclub.org/airst...gas-generator/
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Old 05-15-2024, 10:09 AM   #12
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Getting a few hundred watts of solar would be a good approach but I would go with a reputable brand of panels and use a Victron Solar Controller.

I would not recommend you try to charge from an external charger. A couple of reasons to just plug your airstream directly into the generator (if you need more than you are getting from solar).

Typically it is not good for generators to run for long periods with light loads. So if you are running it to charge the battery you might as well use some of the generator power for other things on the trailer like appliances, hot water heater, etc.

Your airstream installed charger will probably provide faster charging than many external chargers. Plus it requires no wiring changes. Having said that if you really want to be able to easily dry camp invest in a well designed lithium/solar setup and a larger inverter.
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Old 05-16-2024, 05:50 AM   #13
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Quote:
Originally Posted by kenfconnor View Post
.....

Typically it is not good for generators to run for long periods with light loads. So if you are running it to charge the battery you might as well use some of the generator power for other things on the trailer like appliances, hot water heater, etc.

.....
Hi

Any internal combustion engine is going to be stressed by running at or near idle for long periods of time. Indeed, generators are no exception.

The typical converter charger *might* put out 600W ... maybe. A better bet is that it puts out 400W. At 90% efficiency (again a maybe) you are up around 660 and 440 W into the device.

Something like a 1KW generator would be a good match for this sort of load. The next issue is the short time spend on full charge (so 400W) and the long time spent on "tail charge" ( so << 400W). Still it's a better match than the great big beasts a lot of us haul around.

If this is an issue, the "real answer" is to go to lithium's (and a good charger). They will take the full output of the charger just about right up to the end of the cycle. A "real 50A" charger will get a 100AH battery charged from dead flat in 2 hours. You get to use all of the rated capacity on a lithium so one battery replaces the two you now have. (or you go with two and double your usable capacity).

Welcome to taking apart an onion ... there's always another layer

Bob
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Old 05-16-2024, 06:59 AM   #14
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I looked up the specs on the Airstream factory installed converters. They supply 25Amps max.

These are much more capable than the average portable battery charger and is more than enough charge current for the standard lead acid batteries that airstream provides for their trailers. Lead acid batteries can't handle large charge currents anyway without damage (unlike lithium).

However, once you switch to a larger lithium battery bank, 25A is not going to charge your battery bank in a reasonable amount of generator runtime. 400 ah battery bank would need 16 hours to charge using a 25amp charger and your generator will not be loaded properly (25a at 12v = ~2.5A at 120v AC).

You will want something like the charging capability of a victron multiplus II at 120A. This will charge a 400ah lithium bank from 0 to full capacity in 3.3hours. It will fully load most portable generators too as 120amp DC = ~ 12A at 120v AC (plus whatever power the multiplus consumes itself when operating). 12amp at 120v = 1440watts.
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Old 05-16-2024, 08:10 AM   #15
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I agree (FWIW) that with a lithium battery conversion a lot of your worries go away. I'll add that if you're on a budget that it doesn't have to break the bank. I have inexpensive lithium batteries ($200ea) in our million-dollar camper and 50A lithium chargers are in the $230 range. A battery monitor (Victron shunt) is around $130 (not necessary but very helpful). It isn't too difficult if you're at all handy. There are lots of threads detailing this.
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Old 05-17-2024, 07:05 AM   #16
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Hi

A lot of this comes down to "use case". Put another way, just why are we worried about charging batteries in the first place?

1) We aren't worried, we're never "off grid" for more than a day or two. This covers a *lot* of folks. Cheap flooded lead acids are a really good answer for them. They can spend the money they save on that next season's campgrounds.

2) We're "weekend campers" and may be at a site with no power. Let's say this involves 4 days away from power. With some trailers (propane fired fridge, no furnace running), a set of AGM's likely do the job.

3) We want to be out in the wild for weeks. Obviously this gets into a bunch of "resource issues". Just looking at power, that same propane fridge trailer probably makes it 6 to 10 days with some set of lithiums. If it's got a bit of fancy stuff on it, 400 AH might be needed.

What can be done to extend all of these:

1) If you are driving each day, a DC/DC converter is the cheapest option. A $100 version will help you in *any* of the cases above. 10 A for 5 hours is 50 AH. Your flooded cells now are into the "many weeks" category. Spend a bit more on the DC/DC and you'll get even more charge.

2) Solar is the thing most people think of right off the bat. How well it does for you depends a *lot* on the conditions. Spending a few thousand dollars on a big solar setup is not unheard of. Getting to >100 AH a day, every day, means a pretty big system (or really good conditions where you camp).

3) Back to the topic at hand, you can carry a generator. This is a *very* common "just in case" sort of thing to do. For battery charging, a ridiculously small / light / cheap unit will do the job.

Fun !!!

Bob
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