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Old 06-26-2018, 07:50 AM   #1
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Brand: Thor Motor Coach
Model: Siesta
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Question about generator, house batteries, and charging time

We have a 2015 Thor Siesta 24' class C, with 2 12-volt coach batteries. When traveling, we typically stay at places without hookups (state parks, for example, or a local park alongside the beach) for a few days, usually moving either every day or every other day - and driving for 2 to 4 hours (on days we drive) usually recharges the batteries. Then we find an RV park with hookups, for luxurious showers, use of the dump station, water refill, occasional laundry, etc.

Anyway, we have been without hookups for 3 days now, and stopped in one place, so no engine charging - and the house battery status indicators showed between 1/3 and 2/3. Maybe the first time ever below 2/3 usage. We don't use much electricity - all LED lights, we don't watch TV. The blower in the furnace is probably the biggest user - and we rarely use that. Altho we have on this trip...

As an aside - I hate ALL of those indicators - SO little info. And some are just wrong - black water goes quickly to 2/3, while gray water never budges from zero - but we can deal with that. It's the lack of useful info that bugs me...

Anyway, today I fired up the generator for probably the first time since we bought the RV. (Microwave powered up so I know generator was working.) I ran it for about 15 minutes, and the battery indicator said fully charged. I was skeptical, but turned it off, and, over the next hour or so, the indicator drifted back down to 1/3 (or more) full.

So, here are my questions. Just roughly, how long should it take to charge the batteries from the generator? Do I need to turn off the generator to get a (somewhat, or more) accurate reading? Is there an easy way to get a more accurate battery charge indication, generally - ie, a better meter?

Any input here would be greatly appreciated.

Thanks
Dan K

PS - I realize the batteries or the generator could be having a problem, but I don't think so. Let's assume not..
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Old 06-26-2018, 08:38 AM   #2
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RE the length of time for the genset to recharge your batteries: as with most things - it all depends. In this instance, on the state of discharge, the condition of said batteries, type and capacity of the battery charger (converter) and genset output. It generally takes quite a while (several times the 15 minutes you mentioned) to (nearly) fully charge batteries that have been depleted by a third of their capacity. BTW discharging batteries below a certain level will severely shorten their lifespan, especially if they are not of the "deep cycle" type -- wet-cell technology batteries also have to be equalized from time to time so they don't fight each other. The OEM battery state indicator is not a good indication of battery status while being charged via the genset due to the way it is interconnected. A more accurate indication of battery status can be obtained after the initial charging cycle has been completed.
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Old 06-26-2018, 10:43 AM   #3
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I’ve done my doghouse but nothing else, made a huge difference in the noise level!!!
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Old 06-26-2018, 12:00 PM   #4
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Generators should be exercised monthly.

With the generator running the converter is charging your battery at a higher voltage than 12.6 VDC so you battery status indicator will almost immediately show fully charged as all it is doing is sensing the voltage.

If you have a 55 amp converter and run the generator for only 15 minutes you have only charged at best 13 amp-hours into your roughly 200 AH capacity batteries. That won't change the state of charge much. You will have to run the generator for at least 2 hours to make a noticeable difference.
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Old 06-26-2018, 12:20 PM   #5
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Yeah the status lights for the waste water are practically useless. You just learn from doing....how often you need to expect to go until dump station time. Fresh water, L.P., are OK. The battery one is only accurate when Not charging. Once you begin charging it's showing that charging is underway, which is a good thing but it has no way of showing percentages of charge. Another thing you learn from doing. Probably a 2 hour travel trip or generator session at a minimum. Then check the indicator once you've shut down again and see how much the batteries have recovered. Make a mental note and then you'll be able to predict how much charge time to expect next time.
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Old 06-26-2018, 12:23 PM   #6
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Plus, if that's original batteries, they may be trying to retire. After 3 years and based on your dependency as you do a lot of dry camping (lots of cycles), I'd just replace them. Waiting for a batteries to competely die will catch you 1,000,000 miles from a battery distributor.
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Old 06-26-2018, 03:21 PM   #7
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[QUOTE=lspotho;127977
So, here are my questions. Just roughly, how long should it take to charge the batteries from the generator? Do I need to turn off the generator to get a (somewhat, or more) accurate reading? Is there an easy way to get a more accurate battery charge indication, generally - ie, a better meter?
Any input here would be greatly appreciated.
Thanks
Dan K
PS - I realize the batteries or the generator could be having a problem, but I don't think so. Let's assume not..[/QUOTE]
A good battery monitor is the TriMetric by Bogart Engineering. What you have on the panel is battery voltage meter. To use it properly, the battery should be at rest for 30 minutes. Heavy draws or charging will distort the true voltage readings. The generator charges the batteries through converter. This is the same system you use when on shore power. For a group 24 flooded battery, the use rating is about 75 amp hours. As you should never draw a flooded battery below 50% rating (12.1 volts resting) to prolong its life, that would equal a total of 75 amp hours total of usable power. Assuming a 55 amp three stage charger, 1.5 hours of charging would get you to an 80% charge (12.5 volts resting), then the charger will switch modes from a bulk charge to a topping (absorption) charge. To fill the batteries the last 20% will take another 2.5 hours. A full battery will read 12.73 volts resting.
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Old 06-26-2018, 03:35 PM   #8
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"Maybe the first time ever below 2/3 usage"


A local parts store (NAPA, Auto Zone, etc.) can do a "load test" on your batteries, assuming they are fully charged. A weak battery drops off charge quickly and depleats faster under use. I would just have batteries tested before re-inventing the wheel. Your batteries are 3 years old and have worked the up and down cycle pretty regularly.
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Old 06-26-2018, 04:15 PM   #9
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Thanks, everyone, for the replies. As I thought about it, I realized the indicator reading while it was charging had to be the result of the charging process itself. I will get the batteries checked, and will take better care of my generator!

Thanks again.
Dan
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Old 06-26-2018, 04:39 PM   #10
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Our friends have a 432 aH battery bank and a residential fridge. It takes them about 6 to 8 hours to recharge the battery bank for their usage rate.
The Onan manual says if you take that size battery bank to 50% SOC and recharge starting at 100 amps it will take 8 hours. The amps will decrease as the batteries charge over time.
If you go to the manufactures web site of the batteries you can get the charge times and voltages.


Properly maintained wet cell deep cycle batteries are good for 6 to 10 years.
The trolling motor battery we have on the boat is going strong at 8 years.
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Old 06-26-2018, 05:53 PM   #11
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Here, you want some battery charging/draw/voltage/amperage info?...

.




hahaha.


So here's a couple tidbits that might help all of you guys-

The first one is don't assume the 55 amp WFCO converter puts out 55 amps. Actually, don't assume ANY charger is going to put out it's max rating for very long in the charging process. That rating is the max and with my having one and having an ammeter on it I can tell you it's only going to come close to 40-45 amps if the batteries are totally dead. And even then, it's only going to put out that 40-45 amps for a couple minutes. If you only have a voltmeter and all you can see is the battery charging voltage, once it drops from charging at 14.xx to 13.xx, you're probably only putting 10 or 15 amps into those batteries. It's gonna take HOURS to charge at that rate.

On the subject of the stock WFCO converter, it's also not that great on voltage control. I NEVER saw mine go to the 13.1v float voltage, it pretty much stays at 13.6v 90% of the time. I replaced mine with a 100 amp PowerMax converter and it actually charges properly, going from full boost charge rate of 14.6v to 13.6v, then down to 13.1v for long term maintenance. It will also pump out some amperage! I've already seen 80-90 amps out of that converter after running the coach batteries down.

The other is charge time on shore or generator power, which will usually be identical btw. With the stock 55 amp converter, you're going to have to run the generator at least a couple, more like 4-5 hours to get the (average size/somewhat depleted on charge) coach batteries back up to 90%. Again, this is because it doesn't really put out that much amperage/voltage in the boost phase, and doesn't stay in that phase very long. If my coach batteries are almost fully dead, I can get them up to 90% or so now with the 100 amp converter/charger by running the generator for about an hour. That's the biggest reason I replaced the stock converter, so I can quickly get the batteries back up when needed. I would say the 100 amp PowerMax converter resulted in more than doubling the charging speed, which means less than half the time needed to run the generator.

The last point is that using battery voltage to determine the level of battery supply amp hours in this situation isn't that accurate. Having just been charging and then shutting off charger will raise the battery voltage for awhile, having any load on the system will lower the voltage, battery temps and of course accuracy of the voltmeter itself are also factors. So saying the voltage is xx.xx so that means my batteries are at xx% isn't really possible. You can get an idea, but it's not exact by any means.

Hope that helps. Here's the link to the charger/converter I put in my Vegas...

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
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Old 06-26-2018, 06:06 PM   #12
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Dan, (OP) I forgot to answer one of your questions...

Here's what I'm using for voltage and amperage displays on my Vegas...

This one gives you DC amperage and voltage, but the switch to toggle the readings is in the back (stupid). You can have it alternate between volts and amps though, but it blinks in ammeter mode which is kind of annoying. I'm using two of them in amp mode only to show amperage out of the converter/charger and amperage in and out of batteries themselves.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

This is what I'm using for voltage display. It can read from two different sources. I only used this type because I also went with the other switches and panel.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

This is similar to the AC voltage/amperage display I'm using...

https://www.amazon.com/gp/product/B0...0?ie=UTF8&th=1

Like you said, stock there's so little info as far as what's going on with the batteries and charging. Obviously I believe knowledge is power. lol. get it?
ugh.
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