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Old 02-10-2019, 08:01 PM   #1
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amps, watts, and volts...oh my

So....we got this Honda EU2200i generator thinking that after a cold night of the furnace running off of our two 12-volt 81 Ah batteries we have, that we would want/need to charge the batteries the next day. I was thinking "Hey - we could just run the generator for 2-3 hours" plugged into the trailer using the regular 15 amp output plugs from the generator to the 30 amp connection on the trailer (using an adapter, just like it was plugged in at home). Our three-stage converter/charger in the trailer is a WFCO WF-9865, which has an output current of 65 amps (whatever that means).

The dealer told me this week I was on drugs and that my trailer's converter/charger only puts out about 1 or 2 amps and that it would take 3 to 6 days to fully charge my trailer using the generator plugged into the trailer. This sounds wrong, but that is what he said.

He then suggested two other alternatives: (1) Use the 12-volt DC output on the generator with the cable connected to one of the batteries, which apparently runs at 8 amps. At 8 amps to charge 162 amp-hours from 50%, that seems to be somewhere around 10 hours of charging???? Still seems long to me...

or (2) get a solar panel, he said. Probably just trying to make a sale again.

Well, I don't want a solar panel. Not just yet, at least. I thought that a generator could get my batteries topped off during the day. Yeah - I know they are gassy and loud, but it is what I have right now.

So...................how long might it take to charge back up depleted batteries using my generator? Should I use the shore power cord to the trailer, or use the 12-volt DC cable/output on the generator instead?

We were so excited to go boondocking this spring/summer when temps still dip down to 25 to 40 degrees at night. Will need heat.
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Old 02-10-2019, 08:21 PM   #2
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I use the shore power plugged into my generator to recharge the battery. Couldn't tell you how long it takes as I have never timed it.
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Old 02-10-2019, 08:36 PM   #3
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I use the shore power plugged into my generator to recharge the battery. Couldn't tell you how long it takes as I have never timed it.
Understood, but the dealer is telling me it will take 50 to over 100 hours of continuous generator running to recharge my batteries just once using such a method. Doesn’t seem right.
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Old 02-10-2019, 08:45 PM   #4
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If you try to back feed thru the converter, yes it would take forever. If you plug your shore power cord into the generator plug (as you would your home), it'll charge with 120V and go much faster.
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Old 02-10-2019, 08:51 PM   #5
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If you try to back feed thru the converter, yes it would take forever. If you plug your shore power cord into the generator plug (as you would your home), it'll charge with 120V and go much faster.
Thanks PamW. That is exactly what I plan to do...plug my shore power cord directly into the generator.

Which means, my 10-gage 30-amp female end to a 30-amp male end, to a dog bone 30-amp female to 15-amp male end into the regular plug in the generator.

Is that what you mean???

If so, that feed STILL goes through my trailer’s converter to charge the batteries. That is what the dealer is saying will take 100+ hours for ONE charge.
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Old 02-10-2019, 09:44 PM   #6
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Battery charger run be generator

I have heard, if your batteries get run down. the best practice is to plug a portable battery charger into your generator and attach it directly to the batteries to charge them quickly. Then plug the TT into the generator to keep the batteries maintained.

No experience with this, just read in another forum.
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Old 02-10-2019, 09:49 PM   #7
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We have stopped at Walmart and rest stops en-route to our destination in very cold weather. One night into low twenties. The heater ran all nite.


The next day while traveling the truck charging system got the battery charged enough to handle another night. I have never gone 3 nights without a full charge. So not sure if that would make it.



Check out this article.


https://www.your-rv-lifestyle.com/ba...while-driving/


Good Luck
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Old 02-10-2019, 09:51 PM   #8
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I have heard, if your batteries get run down. the best practice is to plug a portable battery charger into your generator and attach it directly to the batteries to charge them quickly. Then plug the TT into the generator to keep the batteries maintained.

No experience with this, just read in another forum.
Thanks. Yes - we have a 3.5 amp NOCO Genius battery charger we use to maintain our batteries during the winter or when the trailer is not being used.

I am more referring to how to best recharge depleted batteries during the day after a night of using power for furnace etc. when camping. My options so far are 1. Plug generator into trailer. 2. Connect batteries directly to generator using 12 V DC 8 amp cable, 3. Plug battery charger like my NOCO to generator and then hook that to batteries.

Just trying to figure out the fastest/best way.
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Old 02-10-2019, 09:54 PM   #9
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We have stopped at Walmart and rest stops en-route to our destination in very cold weather. One night into low twenties. The heater ran all nite.


The next day while traveling the truck charging system got the battery charged enough to handle another night. I have never gone 3 nights without a full charge. So not sure if that would make it.



Check out this article.


https://www.your-rv-lifestyle.com/ba...while-driving/


Good Luck
Bill
Thanks Bill! We don’t expect our trailer to run for multiple days without a charging source, but we don’t move/travel during camping trips and so hence the generator.

I didn’t know the connection to the truck would charge the batteries too, though! Cool.
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Old 02-10-2019, 10:17 PM   #10
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Thanks PamW. That is exactly what I plan to do...plug my shore power cord directly into the generator.

Which means, my 10-gage 30-amp female end to a 30-amp male end, to a dog bone 30-amp female to 15-amp male end into the regular plug in the generator.

Is that what you mean???

If so, that feed STILL goes through my trailerís converter to charge the batteries. That is what the dealer is saying will take 100+ hours for ONE charge.
Yes, you'll need a 30A to 15A converter plug.

So does the dealer think that it would take days to recharge if plugged into a house recept? I don't understand what the difference would be? I'd have to look at wiring diagram to see what he's thinking.

And I'll echo above, the trailer battery will recharge while towing, as long as the plug is installed properly (which mine wasn't).

My trailer is parked at a storage unit. No plug, no battery maintainer. It charges on the way out to wherever I'm heading (generally an hour away), battery's charged by the time I get there. (Small trailer, one battery.)
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Old 02-10-2019, 10:27 PM   #11
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Yes, you'll need a 30A to 15A converter plug.

So does the dealer think that it would take days to recharge if plugged into a house recept? I don't understand what the difference would be? I'd have to look at wiring diagram to see what he's thinking.

And I'll echo above, the trailer battery will recharge while towing, as long as the plug is installed properly (which mine wasn't).

My trailer is parked at a storage unit. No plug, no battery maintainer. It charges on the way out to wherever I'm heading (generally an hour away), battery's charged by the time I get there. (Small trailer, one battery.)
Correct - that is what the dealer is saying....that if my two deep-cycle 12 volt batteries are let's say, half charged (50%), then plugging my trailer into my home would only allow 1 or 2 amps to pass through the converter/charger in the trailer to the batteries to recharge. At 81 amp-hours to charge up (2 batteries x 81 amp-hours each x 50% depletion), he is saying it would take nearly 81 hours to bring them to a full charge. Again, seems way wrong. Some articles I found online state that trailer converts can pass 3 to 5 amps to a battery to charge, which would still require 16 to 27 hours to charge from half-full. Seems way too long. The Honda DC 12 volt cable can charge batteries at 8 amps, I believe, but that is STILL 10 hours to get my batteries charged from half-full. Again, assuming I am doing ANY of this math correctly.

In my humble opinion, my Honda EU2200i generator provides, while running, about the same electricity as my house does (Honda states 125 V, 1875 Watts, 15 amps). So again, I was just trying to figure out how long (in general, and with minimal power use in the trailer while the generator would be running) I would have to run my generator each morning to get my batteries topped off from the night before.
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Old 02-10-2019, 11:22 PM   #12
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Got something for your dealer.


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Sorry, just had to do that.
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Old 02-10-2019, 11:29 PM   #13
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You might find some useful information in this file I borrowed from a Tiffin website. Credit to Larry on that site.

Recreational Vehicle Batteries-V3.pdf
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Old 02-11-2019, 04:45 AM   #14
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Correct - that is what the dealer is saying....that if my two deep-cycle 12 volt batteries are let's say, half charged (50%), then plugging my trailer into my home would only allow 1 or 2 amps to pass through the converter/charger in the trailer to the batteries to recharge. At 81 amp-hours to charge up (2 batteries x 81 amp-hours each x 50% depletion), he is saying it would take nearly 81 hours to bring them to a full charge. Again, seems way wrong. Some articles I found online state that trailer converts can pass 3 to 5 amps to a battery to charge, which would still require 16 to 27 hours to charge from half-full. Seems way too long. The Honda DC 12 volt cable can charge batteries at 8 amps, I believe, but that is STILL 10 hours to get my batteries charged from half-full. Again, assuming I am doing ANY of this math correctly.

In my humble opinion, my Honda EU2200i generator provides, while running, about the same electricity as my house does (Honda states 125 V, 1875 Watts, 15 amps). So again, I was just trying to figure out how long (in general, and with minimal power use in the trailer while the generator would be running) I would have to run my generator each morning to get my batteries topped off from the night before.
I recently let our one battery discharge parked at home accidentally. Using an extension cord and adaptor. The trailer recharges the battery in not more than 5 or 6 hours. So I gotta agree that dealer is **********.

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Old 02-11-2019, 05:23 AM   #15
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So....we got this Honda EU2200i generator thinking that after a cold night of the furnace running off of our two 12-volt 81 Ah batteries we have, that we would want/need to charge the batteries the next day. I was thinking "Hey - we could just run the generator for 2-3 hours" plugged into the trailer using the regular 15 amp output plugs from the generator to the 30 amp connection on the trailer (using an adapter, just like it was plugged in at home). Our three-stage converter/charger in the trailer is a WFCO WF-9865, which has an output current of 65 amps (whatever that means).

The dealer told me this week I was on drugs and that my trailer's converter/charger only puts out about 1 or 2 amps and that it would take 3 to 6 days to fully charge my trailer using the generator plugged into the trailer. This sounds wrong, but that is what he said.

He then suggested two other alternatives: (1) Use the 12-volt DC output on the generator with the cable connected to one of the batteries, which apparently runs at 8 amps. At 8 amps to charge 162 amp-hours from 50%, that seems to be somewhere around 10 hours of charging???? Still seems long to me...

or (2) get a solar panel, he said. Probably just trying to make a sale again.

Well, I don't want a solar panel. Not just yet, at least. I thought that a generator could get my batteries topped off during the day. Yeah - I know they are gassy and loud, but it is what I have right now.

So...................how long might it take to charge back up depleted batteries using my generator? Should I use the shore power cord to the trailer, or use the 12-volt DC cable/output on the generator instead?

We were so excited to go boondocking this spring/summer when temps still dip down to 25 to 40 degrees at night. Will need heat.
I am thinking the Dealer is closer to right than wrong. Your converter has three modes that it charges at. It probably starts out at around 14.4 vdc and around 5 amps then as the battery charges drops eventually to a trickle charge of around 1amp. It could take your converter a full day (24 hrs) to get to 90% then another day on float to get to 100%. If your only charging 2 or 3 hours a day on your generator you can see how long that might take.
Honda does make a battery charging cable that connects directly to the generator and batteries for higher amp output than your are getting from your converter. But even this I don't think will work long term. You just can't seriously run your generator long enough.

Not all trailer connections are wired to charge the batteries from the tow vehicle as your driving, mine isn't. Mine is wired for backup lights.

I have four 12v deep cycle batteries. When dry camping I am not shy about using power for TV and lights(led) but I try to avoid running the furnace. I run my Honda 2000 generator about 4 hrs a day and I can watch my battery volt meter drop a little each day. After 7 to 10 days I have to find a place where I can plug in for a few days to fully charge my batteries.

Also after you have charged your batteries for several hours and you think they are fully charged because they say 12.7v+. Let the batteries rest for an hour and test it again. I think you will find that they did not fully charge with a standard converter in that amount of time.

My plan is to get a minimum 200 watt portable solar panel with controller so when your gone during the day you will be charging those batteries.
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Old 02-11-2019, 10:30 AM   #16
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You need to find another dealer...

I am going to hazard a guess that you probably have a WFCO WF-8955 converter. It should charge the batteries to 80%+ in 2-3 hours from 50% (which you do not want to drop below). The last 20% will take another 4 hours or so. Which may be what the dealer is getting at. You will get better charging from using your on board converter/charger than using the 12v leads on the generator. The only way around the slower charging would be to upgrade to LiFePO4 batteries and the proper charger for them. Quite expensive.

I have seen a charging curve chart using the WFCO, have to see if I can dig it up. I believe that the WFCO can charge at up to 30 amps in bulk mode, but doesn't like to stay in bulk mode long enough for a proper charge.

FLA (Flooded Lead Acid) batteries can only be charged so fast for so long, then they slow down and take a while for the top off charge. Solar works well for this if you are in an area with enough sunlight.

You should figure on running the generator 5-6 hours a day after a night of heavy draw down. You can use 2 batteries to help with capacity. You also should really consider putting in a proper meter to actually keep track of your usage. My personal preference is the Victron BMV-512, others like the Trimetric. Both are quality meters and will let you keep track of what is going on.


As far as charging while towing... It will depend on the vehicle, the size of the wire, etc. Typically you won't get more than 5-7 amps from the tow vehicle.
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Old 02-11-2019, 03:21 PM   #17
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Wahoo has given great info.
The dealer is mostly wrong, but there's some truth to the claim.
According to your OP, your converter has a 65 amp rating. This means it can deliver up to 65 amps DC if conditions call for it. Such conditions would be a depleted large battery bank. When your converter has 120V AC power (plugged into shore power or generator), it will by default start in bulk charge mode. It will start to deliver amps to the DC charging lines and monitor the voltage that it sees. If your batteries are depleted, let's say they are at around 12.2V. They will happily accept the charging amps and as they do, their voltage will begin to rise. If you have a large battery bank that is at 12.2V, they can accept quite a bit of amps and your converter may indeed crank out full 65 amps. But a smaller battery bank, like your 2 batteries, will see their voltage rising quickly and reaching the setpoint of 14.4V. Once they reach that voltage, your converter will begin to taper the amps down so that the voltage remains constant at that setpoint. It will continue to do this for likely several hours, during which time the amount of amps required to hold that setpoint decreases as well. After a certain amount of time or a certain duty cycle (on/off percentage), depends on the programming of the converter, the converter will drop down to float mode where it holds the voltage constant at like 13.4V. Same concept, it will provide just enough amps to hold that voltage constant.

Another caveat, and maybe what the dealer is thinking of, is that the WFCO brand converters are notorious for not actually achieving the bulk/absorption stage modes. This means it will skip the bulk/absorption charging at 14.4V and go right to float at 13.4V. This means that it will indeed take many many hours to reach full charge. But you will still get meaningful charge initially on a depleted battery bank.
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Old 02-11-2019, 04:51 PM   #18
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Well, regardless of what your converter is charging at it's not working for you. So, your going to have to come up with plan B. Running the generator for many more hours, by-passing the converter and charging directly to the batteries with the generator, solar or adding more batteries......
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Old 02-11-2019, 07:23 PM   #19
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Agree with above...the 30 Amp AC plugged into the generator(with adapter) will work just fine for most situations. The issue your dealer may be thinking of is the 12 volts coming off the the TV while running down the road is a trickle charge. That's what's it's designed to be. But yes, the converter in your RV will charge your battery in a reasonable amount of time.

I would run the 12 volt DC direct to the battery from your genny. But understand that the DC circuit is not regulated ...IE...it will over charge quickly as it's a constant 12volt 8amp output. At least that's the warning I get on my brand new Honda 2200i.
So, yea....run the genny for an hour, charging at it's rated DC output, then switch over to the RV 30Amp AC plug and let your on board converter continue to safely charge the battery the rest of the way.

Make sense?
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Old 02-11-2019, 11:10 PM   #20
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Remember that any battery charger slows down as you near a complete charge. Charging daily will only give at best 4 amps per hour with any charger. Running a generator for only 4 amps is not very fuel efficient. It's best to run down the battery to 70% and then charge using a smart charger either on a generator or plugged into shore power. This way it'll initially charge at 8-12 amps per hour making generator charging much more efficient both in amps charged and fuel burned.

I would only use the generator battery charger in an emergency and never for routine charging.
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