amps, watts, and volts...oh my

[1l243]

OP's furnace is 19,000 btu non ducted so it uses less amps (2.7) What some have been referring to 8 to 10 amp draws are for larger 30,000+btu ducted furnace.

When calculating battery ah's I don't think you can count on all those ah's. If you have a 85ah battery and run 8.5 amps for 10 hrs you will have a 100% dead battery. Most don't let their batteries drop below 60%

It would be a good idea to add up all the dc devices used between 8pm when you usually don't run your generator til 8am.

[persistent]

Originally Posted by Beachbourbon

This will recharge your battery In minutes...just plug into your generator, charge up, them maintain as usual with you WFCO. Just one of many options

https://www.harborfreight.com/10250-...art-60653.html

The only reason to use this device to charge a TT house battery is in an emergency to get your electric jacks or slides to work.

The 50 amp setting is intended to get a engine start battery charged enough so that the 50 amp output plus the newly awakened battery can start the engine. In "minutes", you get nothing like a full or even 50% charge. A 160 amp/hour deep draw battery bank can absorb the 50 amps if it is at 10% to start with, but the current must taper off as the charge continues. Forcing the current at 14 or more volts during late charging will grossly over charge causing extreme venting of hydrogen gas.

The 5 and 10 amp settings are going to take a very long time to charge a deep draw to anything resembling 90%.

Almost any TT converter charger will do a better job without over charging. A modern 50 amp converter/charger will do a much faster and better job and provide much longer service life from the batteries.

[Beachbourbon]

Originally Posted by persistent

The only reason to use this device to charge a TT house battery is in an emergency to get your electric jacks or slides to work.

The 50 amp setting is intended to get a engine start battery charged enough so that the 50 amp output plus the newly awakened battery can start the engine. In "minutes", you get nothing like a full or even 50% charge. A 160 amp/hour deep draw battery bank can absorb the 50 amps if it is at 10% to start with, but the current must taper off as the charge continues. Forcing the current at 14 or more volts during late charging will grossly over charge causing extreme venting of hydrogen gas.

The 5 and 10 amp settings are going to take a very long time to charge a deep draw to anything resembling 90%.

Almost any TT converter charger will do a better job without over charging. A modern 50 amp converter/charger will do a much faster and better job and provide much longer service life from the batteries.

You are apparently not familiar with this charger at all, so I’ll ignore the snark and misinformation you posted. For example, this unit cannot overcharge because in automatically switches to trickle charge once charged. Bottom line, it works for me, and I spent my valuable time posting as much...take it for what it’s worth to you or don’t.

[persistent]

I apologize. I did not mean to offend you or to provide misinformation.
I read the advertisement more carefully. I agree with you.
I have one that looks similar in my garage. It works as I have described. I used it for the purpose I described. It is more than thirty years old.
Things have changed.
I stand corrected.

[Firstime RVer]

Hey Aaron,
Its been a while since I've posted here and its good to see you still posting!!


You've been right "on the money" all along.


Based on my experience, a 4 hour charge from my generator or shore power pretty much brings my two 6V golf cart batteries (total 235 AH) up to just about a full charge. My WFCO converted delivers up to 55 amps 12V power.
There are limits as to how fast you can charge batteries to avoid boiling off electrolyte and the smart converted does taper off the charge rate as you approach full charge levels. I am also pretty careful about drawing the charge below 40 to 50%.


Running your furnace while on battery power will draw the batteries down. Based on my last boondocking trip, I made it a point to warm up the trailer while on generator power. Once the trailer is warm the furnace fan which draws about 10 amps will run less than half the time to maintain the set temperature. On our last trip, I estimated that to be about 60 amp hours to run the furnace for 12 hours. That would leave about 60 amp hours to run lights, water pump along with a few hours of TV, without drawing the battery down below roughly 50% charge level.


Charging a battery from an unregulated source is only a good idea a smart charger is not available, with a potential to significantly reduce battery life.


Couldn't resist putting my 2 cents in on this topic

All the best to all and safe travels.
Pat

[Beachbourbon]

Originally Posted by persistent

I apologize. I did not mean to offend you or to provide misinformation.
I read the advertisement more carefully. I agree with you.
I have one that looks similar in my garage. It works as I have described. I used it for the purpose I described. It is more than thirty years old.
Things have changed.
I stand corrected.

Thanks Paul,

I really appreciate this post. We are all here trying to help and make this forum helpful based upon our own experiences. No harm no foul, thanks again and happy camping!

[Hart_family]

Originally Posted by Beachbourbon

This will recharge your battery In minutes...just plug into your generator, charge up, them maintain as usual with you WFCO. Just one of many options

https://www.harborfreight.com/10250-...art-60653.html

Beachbourbon -

The reviews of this Harbor Freight charger are fairly nebulous. I am glad it works for you. Not sure what "in minutes" means. Flooded lead-acid batteries are really not supposed to be discharged below 50%, so to get a 162 Ah battery pack back from 50% (81 Ah) to say 90% or more only takes a few minutes? A modern 65-watt converter would take at least an hour with little/no other electrical use in the trailer. Again, I don't know how to account for efficiencies or the "slowing of the charge" as the battery becomes closer to full. Hmm...

[larrypride]

All this depends on what all those devices are rated for. Start at your house or gen. It you have a 15 amp circuit coming from your house or gen. That’s all you will get. Look at the breaker on your gen. If you plug a big charger into the gen you will over load the gen and the breaker will trip. If your at a camp ground or you get a bigger gen you could plug a bigger charger into the gen or shower power and charge faster. If I was boon docking I would get a couple really large batteries and depending on your truck if it has a big alternator you could charge them really fast. It all depends on how much power (amps) you need.

[Raven71]

I use a trickle charger that I would use on a regular car battery. I charge one battery from a total dead battery in about 4 hrs. I have no shore line anymore. I'm going to run a new one to keep my trailer plugged in. But on one battery I could run my heat all night with no problem. If I don't use anything but my lights. My battery stays charged for at least 4 days.

[leisuresolar@gmail.com]

There is a lot of mis-information out there about charging batteries on trailers. Your dealer was simply wrong. The easiest and quickest way to recharge your batteries is from your generator (with the 30A to 15A adapter) or from shore power. Here are some thoughts for you (with a lot of rounding off for simplicity):

1) Your furnace probably draws 6-8A from the batteries. Depending on how cold it is, it might draw 50AH from your 162AH battery bank in 10 hours. Of course, there are other 12VDC loads in the trailer, depending on lights and radios and other stuff. So your battery might have lost much more than 50AH. Let's say your battery lost 100AH overnight. Since batteries are only about 80% efficient, you will need to put about 120AH back into them to get them back to full charge.
2) Your WFCO panel/charger works like this:
1. When you first apply shore power, either from the generator or from a pedestal in an RV park, the WFCO will go to BULK charge mode. In BULK charge mode, it will attempt to apply 14.4V to your battery bank. While this theoretically will put up to the full 65A into the battery, in most cases you are lucky to get 30A (I'll explain in a minute).
2. When the WFCO detects your battery has reached about 80% charge, (which it doesn't do accurately, I'll explain in a minute), it will then go into ABSORPTION mode, which is about 13.6-13.8V. It then tries to put about 5A into the battery for about 2 hours.
3. After that, the WFCO will go into FLOAT mode, which is 13.2V. In FLOAT mode, it will put less than 2A into the battery.
1. NOTE: SO YOUR DEALER WASN'T COMPLETELY WRONG, SIMPLY TURNING ON YOUR GENERATOR COULD TAKE DAYS TO FULLY CHARGE YOUR BATTERY, BUT HE WAS WRONG NOT TO EXPLAIN WHY.
3) The problem is both in the WFCO and in your trailer wiring. Most trailer wiring between the WFCO and the battery is way too small. This means that the WFCO cannot put the full 65A into your battery, but usually you are lucky to get 30A. Also, the WFCO cannot properly detect the battery voltage, so it prematurely switches from BULK mode to ABSORPTION mode. Either way, you usually only get about an hours worth of BULK charge, or maybe 30AH before your generator/shore power is no longer efficiently charging your battery.
1. HERE IS ONE TRICK TO GET MORE CHARGE. Turn off the circuit breaker to the WFCO charger, then turn it back on, This will fool the WFCO into going back into BULK mode for another hour or so. If you don't know where the circuit breaker is you can accomplish the same thing by unplugging your trailer from the generator/shore power, then plug it back in. This allows another 30AH to go into the battery before it goes into ABSORPTION again. Since you needed 120AH to bring your battery up to full charge (remember our example from item 1 above), you need to do this again and your battery will be close to full charge. Replacing the wiring between the charger and the battery helps a lot, but this can be very difficult to do.
2. Many experienced RV'ers will replace the WFCO charger (not the panel) with a good Progressive Dynamics charger for around $200-$250. While this charger still is limited by the small trailer wiring, it has an option for triggering BULK mode from a button, instead of unplugging the generator. Also, it has better charging algorithms than the WFCO, so will make your batteries last longer.
4) When you are driving, your 7-way plug between your truck and trailer will stuff maybe about 5-8A (often less) into your battery. This is because the wiring in the truck is also too small to put any more current into the trailer. So if you drive for 10 hours, you might put 50-80AH (or less) into the battery. In our example, you needed 120AH to bring the battery fully up, so many people are surprised after driving all day that their trailer battery is not fully charged.
1. HENCE THEY GO TO THEIR DEALER, WHO THEN TRIES TO SELL THEM LOTS OF EXPENSIVE STUFF THAT THEY DON'T NEED.
5) Experienced RV'ers will add a Battery Monitor System (BMS) to their trailer. This allows them to easily monitor how much charge is actually in the battery, as well as voltage and current. Knowing the battery current you can tell how much the truck is putting into the battery, how much the generator is putting into the battery, or how much your trailer (ie the furnace) is pulling out of the battery. Bogart Engineering and Victron both make great battery monitors ($200-$300) and are very popular. You can get a cheap Chinese BMS from Amazon for <$50, but you have no idea of the reliability.


Some lead-acid battery thoughts:
1. Your 161AH battery bank should not be charged faster than 30A anyway. To calculate this, take the full capacity of your battery bank and divide by 5. This is the recommended charge rate for most lead acid batteries. On occasion, it is OK to charge them faster, but it will shorten the life of your batteries.
2. Also, in this example, you discharged your batteries by 100AH, which is known as depth-of-discharge (DOD). Your DOD is 62% (100/161) which will also shorten the life of your batteries. It is generally accepted that 50% DOD is the most you should discharge to maximize battery life.

Some thoughts on Solar and Lithium batteries:
1) Modern lithium batteries do not have any of the same limitations as lead acid. In fact, if you buy a quality brand lithium battery, it will last longer than your RV. Well worth the big investment, considering many people replace their lead acid batteries every 2-4 years. Lithium does not suffer from DOD problems, you can charge them very fast, and they are almost 100% efficient. EVERYONE I know who has bought quality lithium batteries loves them.
2) Solar panels with a good solar charge controller will greatly extend the time between starting the generator or plugging into shore power. This will also greatly extend the life of your lead acid batteries. I use a couple of panels on the roof, and a couple of portable panels that can be set up to 50' away from the trailer, so that I can park in the shade and still get solar power.

Sorry this was so long, hope it was helpful.

[Hart_family]

Originally Posted by leisuresolar@gmail.com

There is a lot of mis-information out there about charging batteries on trailers. Your dealer was simply wrong. The easiest and quickest way to recharge your batteries is from your generator (with the 30A to 15A adapter) or from shore power. Here are some thoughts for you (with a lot of rounding off for simplicity):

1) Your furnace probably draws 6-8A from the batteries. Depending on how cold it is, it might draw 50AH from your 162AH battery bank in 10 hours. Of course, there are other 12VDC loads in the trailer, depending on lights and radios and other stuff. So your battery might have lost much more than 50AH. Let's say your battery lost 100AH overnight. Since batteries are only about 80% efficient, you will need to put about 120AH back into them to get them back to full charge.
2) Your WFCO panel/charger works like this:
1. When you first apply shore power, either from the generator or from a pedestal in an RV park, the WFCO will go to BULK charge mode. In BULK charge mode, it will attempt to apply 14.4V to your battery bank. While this theoretically will put up to the full 65A into the battery, in most cases you are lucky to get 30A (I'll explain in a minute).
2. When the WFCO detects your battery has reached about 80% charge, (which it doesn't do accurately, I'll explain in a minute), it will then go into ABSORPTION mode, which is about 13.6-13.8V. It then tries to put about 5A into the battery for about 2 hours.
3. After that, the WFCO will go into FLOAT mode, which is 13.2V. In FLOAT mode, it will put less than 2A into the battery.
1. NOTE: SO YOUR DEALER WASN'T COMPLETELY WRONG, SIMPLY TURNING ON YOUR GENERATOR COULD TAKE DAYS TO FULLY CHARGE YOUR BATTERY, BUT HE WAS WRONG NOT TO EXPLAIN WHY.
3) The problem is both in the WFCO and in your trailer wiring. Most trailer wiring between the WFCO and the battery is way too small. This means that the WFCO cannot put the full 65A into your battery, but usually you are lucky to get 30A. Also, the WFCO cannot properly detect the battery voltage, so it prematurely switches from BULK mode to ABSORPTION mode. Either way, you usually only get about an hours worth of BULK charge, or maybe 30AH before your generator/shore power is no longer efficiently charging your battery.
1. HERE IS ONE TRICK TO GET MORE CHARGE. Turn off the circuit breaker to the WFCO charger, then turn it back on, This will fool the WFCO into going back into BULK mode for another hour or so. If you don't know where the circuit breaker is you can accomplish the same thing by unplugging your trailer from the generator/shore power, then plug it back in. This allows another 30AH to go into the battery before it goes into ABSORPTION again. Since you needed 120AH to bring your battery up to full charge (remember our example from item 1 above), you need to do this again and your battery will be close to full charge. Replacing the wiring between the charger and the battery helps a lot, but this can be very difficult to do.
2. Many experienced RV'ers will replace the WFCO charger (not the panel) with a good Progressive Dynamics charger for around $200-$250. While this charger still is limited by the small trailer wiring, it has an option for triggering BULK mode from a button, instead of unplugging the generator. Also, it has better charging algorithms than the WFCO, so will make your batteries last longer.
4) When you are driving, your 7-way plug between your truck and trailer will stuff maybe about 5-8A (often less) into your battery. This is because the wiring in the truck is also too small to put any more current into the trailer. So if you drive for 10 hours, you might put 50-80AH (or less) into the battery. In our example, you needed 120AH to bring the battery fully up, so many people are surprised after driving all day that their trailer battery is not fully charged.
1. HENCE THEY GO TO THEIR DEALER, WHO THEN TRIES TO SELL THEM LOTS OF EXPENSIVE STUFF THAT THEY DON'T NEED.
5) Experienced RV'ers will add a Battery Monitor System (BMS) to their trailer. This allows them to easily monitor how much charge is actually in the battery, as well as voltage and current. Knowing the battery current you can tell how much the truck is putting into the battery, how much the generator is putting into the battery, or how much your trailer (ie the furnace) is pulling out of the battery. Bogart Engineering and Victron both make great battery monitors ($200-$300) and are very popular. You can get a cheap Chinese BMS from Amazon for <$50, but you have no idea of the reliability.


Some lead-acid battery thoughts:
1. Your 161AH battery bank should not be charged faster than 30A anyway. To calculate this, take the full capacity of your battery bank and divide by 5. This is the recommended charge rate for most lead acid batteries. On occasion, it is OK to charge them faster, but it will shorten the life of your batteries.
2. Also, in this example, you discharged your batteries by 100AH, which is known as depth-of-discharge (DOD). Your DOD is 62% (100/161) which will also shorten the life of your batteries. It is generally accepted that 50% DOD is the most you should discharge to maximize battery life.

Some thoughts on Solar and Lithium batteries:
1) Modern lithium batteries do not have any of the same limitations as lead acid. In fact, if you buy a quality brand lithium battery, it will last longer than your RV. Well worth the big investment, considering many people replace their lead acid batteries every 2-4 years. Lithium does not suffer from DOD problems, you can charge them very fast, and they are almost 100% efficient. EVERYONE I know who has bought quality lithium batteries loves them.
2) Solar panels with a good solar charge controller will greatly extend the time between starting the generator or plugging into shore power. This will also greatly extend the life of your lead acid batteries. I use a couple of panels on the roof, and a couple of portable panels that can be set up to 50' away from the trailer, so that I can park in the shade and still get solar power.

Sorry this was so long, hope it was helpful.

LeisureSolar - yes, great post and VERY helpful! I think we have reached a general consensus on the science/facts, and you have hit most points very well. A few things I might add/edit:

1. The amp draw of my particular heater is less than 3.0 amps. It is a 19,000 BTU direct discharge.

2. And yes - the dealer said that RV converters in general charge at 1 amp, period. Of course, that was not correct nor that simple.

3. Interesting about the WFCO not sensing the battery levels, but going to a predetermined bulk, absorb, float mode for different periods of time. I believe you. However, when I called WFCO, they said the converter/charger will send as many amps as "the battery will accept". Not really sure what that truly means. haha

4. I would rather save my money on a Battery Monitoring System/Kit and am going to lithium batteries anyhow. Lithium batteries will will "accept" more charge and at a significantly faster rate. They are considered "drop in" due to the BMS on the battery itself. However, the WFCO charger may still only send what it is already sending (e.g., 2 hours in bulk) because it doesn't know or care that I have lithium. I am calling WFCO tomorrow to discuss just so I can make some informed decisions. WFCO and perhaps other manufacturers make converters/chargers specifically for lithium, so I will keep studying this.



2.

[persistent]

Originally Posted by leisuresolar@gmail.com

There is a lot of mis-information out there about charging batteries on trailers. Your dealer was simply wrong. The easiest and quickest way to recharge your batteries is from your generator (with the 30A to 15A adapter) or from shore power. Here are some thoughts for you (with a lot of rounding off for simplicity):
...
Sorry this was so long, hope it was helpful.

Thank you leisuresolar for a well thought out detailed post.

I agree with your conclusions. However, others should be cautious about using the converter disconnect and reconnect strategy. It depends on the battery bank size and 12 volt appliance consumption. Small battery banks and low appliance draw can lead to overcharging and shorter battery life.

I looked up the specs for the WFCO WF-9865 converter. It is a 65 amp three stage charger and it works substantially the way you describe.
I agree it may only charge your hypothetical battery bank at 30 amps, but the reason it does so is dependent on more than the size of the wire connecting the battery.
Assuming the wire is large and capable of delivering 65 amps, the initial bulk charge is dependent on the size of the battery bank and the current charge level of the batteries.
A large bank at low charge level could indeed draw much more. The WFCO initial output provides a maximum voltage of 14.4 and a maximum current of 65 amps. The batteries themselves limit the current within those two parameters.
The WF-9865 may never enter balk charge phase unless total current draw exceeds 20 amps. So, a smaller battery bank at 60% charge may not trigger bulk charge at all.

Balk phase:
At a low charge level during the initial balk phase the bank may draw the maximum 65 amps, less what any other 12 volt appliances draw. Of course small gage wire would also limit. The WFCO lowers its output voltage to prevent higher than 65 amps. Typically the current in the bulk phase is constant do to the converter limit. During this period, the voltage will rise slowly until it reaches 14.4 volts thus maintaining the constant current. As the charging progresses the battery internal resistance will increase. The current will drop and the voltage will remain at a constant 14.4 volts.

Absorption phase:
At some point the WFCO will lower the maximum voltage from 14.4 to between 13.8 and 13.6 volts. The purpose is to prevent production of excess hydrogen gas and shortening battery life. That simply means prevent overcharge. This phase continues to charge the battery bank at a lower rate. This phase will probably continue as long as you occupy the TT. Current into the batteries will continue to drop.
WFCO determines the point it switches using current and time. The primary determination is a preset current level. The level may be about 20 amps. I don't know if the user can change the preset. It is probably different for different capacity converters. WFCO makes an assumption about what other appliances might draw and the size of the battery bank.
There is a maximum time limit for the bulk phase of 4 hours. After 4 hours it will switch to absorption regardless of the current.
Rebooting the converter will of course reset the time limit. If you have a very large battery bank, say over 300 amp/hrs, rebooting may decrease your charge time. If you have a small bank, say 80 amp/hrs, it may already be in overcharge mode and be producing a great deal of hydrogen. (This is very bad for sealed AGM or GEL type batteries.) The small bank will not charge significantly faster than if the voltage were lower. The lead/acid chemistry cannot absorb charge any faster. It will simply produce more hydrogen.
Optimum time and current trip point for any battery bank and 12 volt appliance draw is different for every TT configuration. Some converters are programable for the charging parameters.

Float phase:
This phase is intended for use when the TT is not in use but still has shore power available. When current draw does not change in 44 hours, it switches to 13.2 volts. This lower voltage consumes less water during long periods of storage and increases battery life. It will not charge significantly beyond what has already occurred. If the battery is low, charging will continue. As it continues to charge the current will also be dropping. That change in current will prevent switching to 13.2 volts.

WFCO considers 11.9 volts static no load/no charge voltage discharged. 12.7 volts static no load/no charge is considered fully charged. I think that is actually about 10% to 90%. I am not sure about the 90% and not willing to look it up just now.

Other modern converters work in a similar manor. Older converters sometimes had a constant voltage of between 13.2 and 13.8 volts. They do charge batteries. The late phase charging is very slow and putting the last 15% into the battery may take days.

I have attached the WFCO PDF detailing charging theory.

[leisuresolar@gmail.com]

I read about 1/3 of the words in this super long thread. So maybe someone already said this.

1) The WFCO is notorious for having bad charging algorithms.
2) The WFCO is very sensitive to the wire size between charger and battery. This may be the source of the bad charging rumors, but it is certainly true that small wires aggravate the problem.
3) I replace every WFCO in every solar install I do. Their breaker panels are fine, their chargers are junk.
4) If you don't have a good battery monitor, it's all moot. Only with a good battery monitor can you really see what is going on. I prefer the Thornwave Labs bluetooth monitor.

Hope this doesn't add too many words in this super long thread.