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Old 02-22-2016, 05:08 PM   #1
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Charging with generator question

My father-in-law and I went dry-camping this past week in separate trailers, his an '09 Flagstaff 5er and mine a '16 Flagstaff TT. He has a Honda eu2000 generator. I found need to recharge after 2-3 days when my batteries were almost completely down. Some questions/concerns came up as a result of our experiences charging both rigs:

1. Why would my TT put such a heavy load on the generator when first plugged in? My fridge was on propane only (I made this change away from letting it pick automatically), and maybe only 1 LED light was on and 2 devices were charging. Heater was off. For about 20-30 minutes (maybe longer?), the generator was kicked up as if under heavy load and then it would finally kick back down to lower RPM. But even after 2-3 hours on the generator I barely got back to halfway charged. Was it just not enough time on the generator for a full charge? Would a bigger generator give me faster re-charge times?

2. My father-in-law plugged into his trailer and it kicked up RPM's for maybe 5-10 minutes and then it would kick back down to the lower RPM range for the rest of his charge. He also noted that a longer time on the generator didn't give him full charge.

3. With almost completely dead batteries on the way home and plugged into the truck I only got about 3/4 charged on the ~ 2.5 hour trip home. Is this just not enough time to fully charge given the time and vehicle (2015 F-150 EcoBoost)?

Hopefully this is enough info to get some ideas here. My father-in-law believes that the initial draw issues may be in some part due to either a short somewhere or maybe something wrong in the charging system itself (rectifier?).
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Old 02-22-2016, 05:27 PM   #2
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1. You should not discharge you batteries beyond 50% of their capacity, it shortens their life a lot. So does charging too quickly, as it can overheat the batteries.

2. You might try switching off 120 volt circuit breakers just after powering up the generator to see if any particular circuit besides the converter/charger is using much electricity.

3. We can give you better and more specific advice if you will list exactly what batteries you have (Amp. Hours, or at least Group number). Model number and brand of your converter/charger would also be helpful.

4. It is doubtful that a larger genny will decrease charging times. Those times are controlled by the size (capacity) of your converter/charger. A larger converter *may* shorten charging times. There are many factors that effect charging time.

FYI, a 65 amp converter/charger draws a maximum of about 1000 - 1200 watts from the genny.
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Old 02-22-2016, 05:41 PM   #3
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Well, it depends on what you mean by almost completely dead, you shouldn't let batteries get below 12.1V which is 50% discharged. The lower the batteries are the charge time increases exponentially.

I've got a 65 amp converter, and I'd charge everyday which was usually at 12.3V or 70%. The generator would only need about two hours to charge up. But, that would only get me to 95ish% as I didn't want to let it take the time to finish up as that last 5-10% takes a while.

If you're really dead, then initially the converter was working really hard to charge the batteries, drawing a lot of power, which likely explains the high RPM on the generator.

Your father in law could have been discharged less, have a different converter that has a different rate, etc.

Finally, your truck has a probably 12ga wire that's about 18 feet long, it can only flow so much electricity, it's really only there to maintain the batteries while towing, not to charge them from dead.
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Old 02-22-2016, 06:04 PM   #4
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Well, it depends on what you mean by almost completely dead, you shouldn't let batteries get below 12.1V which is 50% discharged. The lower the batteries are the charge time increases exponentially.
Thanks for that! I would have never expected/anticipated that. Based on this then, the fact that the CO2/Propane leak detector malfunction due to low battery means that I went too low. Correct?

I'm assuming here I can test one or both of the batteries with a meter for the volt level/value?
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Old 02-22-2016, 07:19 PM   #5
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Sorry, but it all depends. Actually it seems that your converter stayed in high output boost mode longer since it loaded the genny for a longer time. Now, assuming that you both have the same number of batteries and the same converter, his simply dropped out of boost sooner. However, it takes a long time to get back to 75% or 100% SOC. Batteries can only take current for so long without getting too hot and, as they charge they begin to fight back as the voltage rises. Converters will drop out of boost if they sense a significant back voltage in an attempt to keep the batteries cool. As far as the "long trip home" is concerned, 2-1/2 hours isn't much when the feed line from the TV is long and of a relatively light gauge.

That being said, other posters are absolutely right, going below 50% state of charge is not recommended for lead acid batteries. If you have a real battery monitor (Trimetric or other) they will measure how much current has been put back in and for how long.Since they measured how much came out, it is a relatively easy process for them to give you accurate SOC. Voltage monitors like the LED ones that come with RVs are really of little use in determining SOC. I worried about my 4 12 volt deep cycles a lot until I put in a TriMetric. Now I know not only how much is left in the bank, but also how much is going back in when the engine or generator is running and when connected to shore power. The LEDS really don't help here. Frankly I don't understand why RV manufacturers don't put them in as standard equipment. The total cost is less than $200 and they are well worth it!
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Old 02-22-2016, 10:33 PM   #6
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Thanks for that! I would have never expected/anticipated that. Based on this then, the fact that the CO2/Propane leak detector malfunction due to low battery means that I went too low. Correct?

I'm assuming here I can test one or both of the batteries with a meter for the volt level/value?
In the field I use a voltmeter to monitor my voltage at my fuse box, one day I'll install a permanent voltage display. But to truly measure battery health pick up a hydrometer at a parts store. That will tell you more that just the voltage, which is important, but doesn't tell the whole story.
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Old 02-23-2016, 01:20 PM   #7
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Another thought regarding high amp's while charging is electric. hot water heater switched on. Do you have one and was it on?
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Old 02-23-2016, 04:18 PM   #8
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1. You cannot apply more than 25% of your batteries amp hour capacity in charging current. BIGGER converters won't charge you up fully 1 second faster than a properly sized converter. If you have a couple of group24 batteries that is 150 amp hours so an charger more than 35-40 amps is overkill. Pair of Group 27's are 200 amp hours ...so they can take 50 amps...etc.

2. VOLTAGE is NOT how you determine if a battery is full when it is connected in a coach. That is only good for a static bench test after waiting 24 hours DISCONNECTED after charging! Not real practical in use!
You either need to spend for a REAL battery monitor ($150) or get a turkey baster hydrometer at autozone and test the specific gravity of the cells. SKnight has it right.

3. If you are discharging your batteries to 12.2V then it will take roughly 6 hours to FULLY charge them with a PROPER sized converter and wiring. You can get away with bringing them up to 90% or so with a 2 hour charge for a bit of camping but suggest a full charge at least once a week in use to avoid loss of capacity.
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Old 02-23-2016, 04:20 PM   #9
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Battery Voltage level

We are not full timers but well over 100 nights last year. I wanting to put a voltage meter so I can consistently have a view of my battery condition. I have a 28RKS Wildcat. Does anyone have a recommendation of the best place to wire into the system and mount it. My monitoring panel is half way between the batteries at Gege front and my electrical panel, inverter etc at the rear. I think I'd like to mount it by the existing monitor panel but not sure if there is an accurate tie in point there. I'll wait your comments.
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Old 02-23-2016, 04:38 PM   #10
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Filterman...if you are boondocking rather than plugging in for a lot of that..you should have a battery MONITOR not a VM. You can mount the Victron controller/readout wherever you can reach with the STANDARD PHONE WIRE that connects to the shunt.


Victron Energy BMV700 Precision Battery Monitor Free Shipping | eBay

Trimetric makes a similar instrument that a lot of folks use but it is more expensive and does no more.
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Old 02-23-2016, 04:45 PM   #11
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Filterman...if you are boondocking rather than plugging in for a lot of that..you should have a battery MONITOR not a VM.
Can you please expand on your comments and talk about why this is the case? I think many, including me, would be interested.
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Old 02-23-2016, 05:13 PM   #12
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Originally Posted by camaraderie View Post
Filterman...if you are boondocking rather than plugging in for a lot of that..you should have a battery MONITOR not a VM. You can mount the Victron controller/readout wherever you can reach with the STANDARD PHONE WIRE that connects to the shunt.


Victron Energy BMV700 Precision Battery Monitor Free Shipping | eBay

Trimetric makes a similar instrument that a lot of folks use but it is more expensive and does no more.

Trimetric one will also connect to their solar charger if you go that route.


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Old 02-23-2016, 05:31 PM   #13
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Can you please expand on your comments and talk about why this is the case? I think many, including me, would be interested.
Sure.
First let's dispense with the voltmeter. It CAN show you that your battery is dead. It can show you what stage your charger is in when you are plugged in (i.e 14V+ = bulk mode, 13.5+= absorbtion, and 13.2+= float. If you have a 4 stage charger you will occasionlly see 14.8+ for equalization cycle.)
It CANNOT show you when your battery is full. It cannot show you the true state of charge of your batteries. i.e. 50% full 75% full etc. because voltmeters cannot account for the surface charge put on a battery during charging AND because the batteries are IN USE in the coach. Voltmeters are used to check the state of charge of a static and disconnected battery...you must wait 24 hours after charging a battery on a TEST BENCH to get an accurate voltage reading. You can't get one under active use. I see comments here all the time that say "I charged up my batteries to full"....then say it took an hour or two. Impossible...they are relying on an idiot light or a voltmeter that is reading the surface charge of the battery after they shut off the charger. It takes at least 6 hours of charging to fully charge a battery that is less than half full.

Now what a battery monitor does is to monitor the amps in and out of the battery which is really the basis for a whole host of functions. For example...lets say you have a Group 27 battery with 100 amp hours capacity. If you hook up a battery monitor (more on that later) and you are charging it at 10 amps and listening to the radio at 2 amps and lights & computer and propane montitor are using another 10...then after one hour of use...you will be down 2 amp hours. Your monitor will show you with 98% of capacity remaining.

Lets say a day goes by and you've turned off your charger and you check your monitor and see that you're down to 60%capacity having used 40 amp hours. Your charger is capable of providing (for example) 20 amps of charging current in bulk mode so you crank it up...but you KNOW it is gonna take more than two hours to get 40 amphours back into your battery...because battery charge acceptance goes WAY down as the battery gets closer to 100% charged...and you don't have the full 20 amps available since other stuff in the coach is using some current. The battery MONITOR will let you monitor the whole charging process and you can see exactly when the battery is 90% full or 100% full and you can turn off the genny and charger.

Other neat things...you can turn any single item on and instantly know how many amps it draws so you know how watching four hours of TV affects your battery. You can see how many hours at the present rate of use it will be till your battery will need to be recharged.

NOW...Installation...is quite simple and does not require a pro. First lets review the parts. First you have the monitor itself which is simply a round hole mount. Plugged into the back of it is one end of a telephone wire. 2 seconds! The other end of the telephone wire is run to the battery compartment. The next item is the SHUNT...the thing with the two big screws on it. One end of the shunt gets ALL of the negative wires on you battery attached to it. The other end gets a single negative wire (buy the length you need based on where you're gonna mount the shunt. And that negative wire gets attached to the negative battery terminal. Then there's the little red wire that goes on to any positive battery terminal from the screw on the shunt. Finally you plug the other end of the telephone wire into the hole in the shunt and you are up and running. You'll do some setup at the monitor like telling it what size and type of batteries you have...but that is about it.

Hope that is a helpful overview. Monitors pay for themselves by avoiding premature murder of batteries AND extending the life cycle. They also save money so you don't waste gas and generator time charging prematurely or too long.
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Old 02-23-2016, 05:50 PM   #14
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Red face Battery condition

I may be ignorat, but that's a lot for a volt meter. What am I missing??
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Old 02-23-2016, 06:00 PM   #15
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Filterman...if you are boondocking rather than plugging in for a lot of that..you should have a battery MONITOR not a VM. You can mount the Victron controller/readout wherever you can reach with the STANDARD PHONE WIRE that connects to the shunt.


Victron Energy BMV700 Precision Battery Monitor Free Shipping | eBay

Trimetric makes a similar instrument that a lot of folks use but it is more expensive and does no more.
Thanks for the heads-up. I bought one!
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Old 02-23-2016, 06:06 PM   #16
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Put it this way, the Victron is about $40 less than the Trimetric monitor I installed.

But they are more than a voltmeter! Camaraderie does a good explanation of the difference.
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Old 02-23-2016, 06:18 PM   #17
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Thanks for that! I would have never expected/anticipated that. Based on this then, the fact that the CO2/Propane leak detector malfunction due to low battery means that I went too low. Correct?

I'm assuming here I can test one or both of the batteries with a meter for the volt level/value?

Instead of plugging the TT in to use the converter to charge your batteries , use a separate battery charger . I run 4 100 amp hr batteries with a separate battery charger of 15 amps i get roughly 3.2 amps per battery charge rate and it can take up to 24 hrs to get a full charge .
charging a single battery with much more the 15 amps is not good and i lower amp charge rate will give you a fuller charge then a 50 amp shot for 2 hrs
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Old 02-23-2016, 06:34 PM   #18
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I may be ignorat, but that's a lot for a volt meter. What am I missing??
Only the first paragraph talks about voltmeters. "Now what a battery monitor does....." begins everything that is different about a battery monitor vs. a voltmeter.
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Old 02-23-2016, 06:46 PM   #19
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I'm with Northstar 1960. I've had 3 rigs and none ever produced over 3 amps charging. I carry a seperate 15 amp charger with 50 amp boost. Can now boost daily on 15 amps and accomplish what took 24 hours in 2 hrs. I must charge daily to not overdraw.
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Old 02-23-2016, 06:51 PM   #20
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charging a single battery with much more the 15 amps is not good and i lower amp charge rate will give you a fuller charge then a 50 amp shot for 2 hrs
Disagree..ideally the most efficient way to charge a 400 amp bank is to size the charger close to 25% of the amp hour rating or close to 100 amps.
(see IOTA Product Specifications with IQ4 module for example)

Let's assume you discharge to 50% and need to put back 200 amphours. That would take about 6 hours with the DLS90...a bulk phase at 90 amps for 1.5+hours then a ramping down of the voltage and current to less than 4 amps and 13.2 volts float voltage.
There is no reason other than cost, not to charge as quickly as the battery chemistry will allow. Modern chargers & increasing resistance will taper and lower amps&voltage appropriately. Charging with LESS than 10% current as you do actually fails to stir up the battery fluid sufficiently and requires more frequent equalization cycles to preserve battery cycle life from sulphation. I suggest a minimium 40 amp charger for your application and you will also shorten your charge time by more than 35%.
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