Difference in Charging Between Generator and Shore Power

[Al and Missy]

There should be no difference between charging on the generator and shore power. The generator is just an alternate source of shore power.

Al

[ROBERT CROSS]

Originally Posted by AzAirstream

What about charging the batteries with an external 15 amp or more charger off of the A/C plug on the generator, not thru the trailer system?

Because the AS charger is a 55a charger, and even that's not enough for the OP.

Bob
🇺🇸

[AirMiles]

Originally Posted by ROBERT CROSS

Because the AS charger is a 55a charger, and even that's not enough for the OP.

Bob
����

The AS charger will NEVER put 55A to the batteries. More likely less than 10A at 13.8V from the readings on my 27' Airstream. My PD4655 isn't much better, but at least it charges at 14.2V. This is why I need to boost charge with my generator and PD4655 for at least five hours to get out of bulk mode when my batteries are depleted. If it was putting 55A to the batteries, it would only take an hour or two to completely charge the batteries.

The only way I can put serious amps to the batteries is with my solar. I've documented my 400W of solar putting 30A to the batteries and the best I've seen, with limited use, on my 600W of solar is 38A. Shore power chargers are designed to charge slowly over days of continuous charging while connected to shore power. I've documented the slow charging capability of the WFCO 8955 on my 2018 27' Airstream here: https://www.airforums.com/forums/f44...ml#post2291015 "I ran the batteries down to 12.11V. Then I turned on the WFCO on 120V. It started in Bulk mode at 8:15pm at 12.45V. At 9:04 voltage was at 13.04V. At 11:16 it was at 13.23V. At 12:02am it was at 13.27V. At 12:46 it was at 13.33V. At 1:33 it was at 13.37V. At 2:45 it was at 13.42V. At 4:54 it was at 13.49V. At 6:07 it was at 13.52V." It took 10 hours in bulk mode to raise the battery voltage from 12.11V to 13.52V. Not very impressive.

[ROBERT CROSS]

^
?

I don't recall saying anything about amps.
The 6v Trojans need a 14.8v bulk, which I don't believe the OP charger can supply.

Bob
🇺🇸

[Al and Missy]

The amount of current going into the batteries is dependent on the battery composition and the voltage applied. At 13.6 volts the current into either conventional or golf cart batteries is quite low. Just because the converter is capable of putting out 55 amps doesn't mean the batteries will accept it. Trojans used to recommend a charger putting out a constant current of C/.25 or so where C is the battery capacity in Ah until the voltage reaches 14.x volts at which point the battery is about 80% charged. The charger would then switch to a constant voltage around 13.6 until the current declines to a low value then go into maintenance mode at about 12.6 volts. Charging at C/4 would then take something over 4 hours to get to 80%. Getting the last 20% would take even longer.

Al

[guskmg]

The only way I know to increase battery charging is to use solar, already mentioned, and /or an inverter charger. They can be programed to higher rates than recommended for the batteries so be careful.
guskmg

[Alumineer]

Originally Posted by ROBERT CROSS

Maybe this a dumb question, (but consider the source).
Does the 9855 have the correct charge profile?
You may need a bit more punch, especially for equalization.

Bob
🇺🇸

This post by Robert is the key. Different battery chemistries require different voltage thresholds (that are temperature dependent) to achieve full charge in an given time, without incurring damage. Many converters do not have sufficient adjustability to do more than partially restore charge, especially for high capacity cells like the Trojans.
Additionally, the tow vehicle's 12V output is generally not high enough to perform significant charging, both because of the length/gauge of the cabling and because the tow vehicle's 12V system is designed around charging its starting battery and not some unknown trailer battery.
The 12V output from portable generators is also generally not designed to actually charge a battery. The voltage is not high enough and the current is insufficient to charge anything in a reasonable timeframe.

If you have high performance batteries like the Trojans (or a lithium bank) you need to invest in a high performance charging solution that can be configured to the requirements of the battery. The good thing is that such chargers typically don't cost more than a couple hundred dollars, which is less than the batteries.

[uncle_bob]

Hi

Unless you want to see steam shooting out of your batteries, doing crazy things with charge profiles is a bad idea. Lead acid batteries take a long time to go from 80% to 100% charge levels. If it's hot out they may be going from 80% to 120% ....

All the magic voltages on batteries vary with temperature. If the batteries are down at freezing, that's very different than being up around 120F in the hot sun. A charger that has no idea of the temperature is not going to do as good a job at the extremes.

Any conventional charger puts a voltage on the wiring at the charger output. If there is a lot of current flowing, the voltage at the battery will be lower. That's just how wires work. As noted above, the current involved at any specific voltage may be quite a bit or it may be very little. It all depends ...

If you are charging up before a trip, leave the converter / charger on at least overnight. Resist the temptation to turn on the furnace. Better yet, run it for 24 hours before you take off on a trip. If you really are getting a max of 10A out of your converter and are half way down on 200AH of battery ... and putting 4A into the furnace .... 24 hours isn't going to be enough .... It may not be enough even with the furnace off.

Bob

[dzwiss]

Originally Posted by AzAirstream

What about charging the batteries with an external 15 amp or more charger off of the A/C plug on the generator, not thru the trailer system?

This is exactly what I do. I only have a 1000 watt Honda generator, which isn’t enough to run a 55 amp converter. I also have a 25 amp automotive smart charger that will put out a full 25 amps for over an hour before it starts tapering down, then over 15 amps for another hour before I shut it down. This setup with the addition of factory solar serves us well when off the grid. We get along quite well on 50 amp hours per day. The one improvement I would like to make is to replace my WFCO 55 amp converter with a Progressive Dynamics 40 amp converter so I could plug the genny directly into the AS and save messing around with hooking up the charger. Oh yeah, and replacing the factory solar charge controller with something a bit more sophisticated. One thing I do like about my setup is the 1000 watt generator. It is extremely light weight and economical. Up to six hrs on 1/2 gal of gas.

[uncle_bob]

Originally Posted by dzwiss

This is exactly what I do. I only have a 1000 watt Honda generator, which isn’t enough to run a 55 amp converter. I also have a 25 amp automotive smart charger that will put out a full 25 amps for over an hour before it starts tapering down, then over 15 amps for another hour before I shut it down. This setup with the addition of factory solar serves us well when off the grid. We get along quite well on 50 amp hours per day. The one improvement I would like to make is to replace my WFCO 55 amp converter with a Progressive Dynamics 40 amp converter so I could plug the genny directly into the AS and save messing around with hooking up the charger. Oh yeah, and replacing the factory solar charge controller with something a bit more sophisticated. One thing I do like about my setup is the 1000 watt generator. It is extremely light weight and economical. Up to six hrs on 1/2 gal of gas.

Hi

A 55A converter will take in a bit more than 5.5A *if* it is putting out 55A. As noted earlier in the thread, it likely is putting out something less than 30A. If your fridge is on propane, a 1000W generator should have no problem at all running your converter / charger.

The "charge output" of the generator is very poorly regulated. Whatever it's doing to your batteries .... yikes ( so don't go there either ...).

Bob

[ROBERT CROSS]

Originally Posted by uncle_bob

Hi


The "charge output" of the generator is very poorly regulated. Whatever it's doing to your batteries .... yikes ( so don't go there either ...).

Bob

If trailer batt's are charging from the genset directly to the batt's, that IS bad.👎

Regardless, the charge output of our Honda is only 8a, can't expect much there.

We always run SP directly from the Honda AC.

Bob
🇺🇸

[Justinfinity]

This is an interesting thread, with a number of relatively accurate observations about voltage and current. However, there hasn't really been any discussion about the fact that conventional non-Lithium lead acid/AGM batteries have a declining Charge Acceptance Rate. No amount of charging power from ANY source, whether shore, generator, or solar, will solve the problem of the declining charge acceptance rate that is inherent in conventional lead acid batteries (in any series/parallel 6V or 12V configuration).

Roughly speaking, below 85% state of charge (SOC), you'll get a bulk charge current of close to the maximum output of the charge source. However, as the SOC goes past 85% on its way to 100%, the conventional lead acid batteries will refuse current and their rate of charge will decline into low single digits of current (4,3,2,1 Amps) until they reach 100% SOC usually after many hours.

The time it takes to get from 85% to 100% may be many times longer than the time it takes to go from 50% (or lower) to 85%. Further, if you keep cycling the batteries between your deepest discharge and 85% or 90% without taking them back to 100%, they will sulfate and eventually lose capacity and die.

One of the most effective things you can do is spend the money on batteries that have the highest Charge Acceptance Rate possible, either AGMs such as Northstar thin plate AGMs (which I have on my boat) or LiFePo4 Lithium (low temperature) batteries (which I have on my Airstream).

I have taken my Airstream to Canada in sub-zero temperatures, running the fridge, furnace, lights, TV, etc all week and kept the batteries at 100% without having to plug into shore power, using 6x100 watts of solar (yes, even in the Great White North with snow on top of the panels) and a robust alternator connector from my tow vehicle. I have been meaning to post more detail about my installation, complete with photos. If there is interest, I will do so. The system has been outstanding.

[RJKSr]

If your converter/charger is similar to the one they install in newer Airstreams, I suspect that is the issue. Our 2017 came with the a Parallax 5355 and two 12V Interstate 75AH batteries. We too experienced poor charging with the generator because it used the Parallax 5355 when plugging the trailer into the generator. I discovered that the Parallax max charge was 13.2V, which is OK for maintaining a float charge, but cannot provide an adequate charge to batteries that are close to a 50% discharge.

Parallax engineers said this was to prevent "boiling" batteries dry and suggested installing their Tempassure 4400TAU unit which allows a higher charge rate because it provides temperature compensation. After installing it, I can get +14V with it ... sometimes.

then installed solar which helped because it can charge above 14V in full sun. Later installed two 6V 120AH batteries in series because the Interstates would not last 2 days while boondocking in cloudy weather. That gave us 45 more AHs. The real solution is to change out the Parallax unit with on that has a true multistage charger. For now, we are going to use the 6V batteries for more of their lifetime and then change out the charger to one that can also do Lithium so we can move to higher capacity and better performing Lithium batteries.

[Gcragg]

This is a good example of why I’m alittle upset with AS forcing these compressor type fridges on us.
I like Boondocking. AHrs are important for us to keep low.
Why?? ...would we want to have to run an electric only fridge.
I guess this is what happens when AS buyers are considered as RV park queens. As sadly. Most are.

[MissingLink5]

Originally Posted by Blu_Hwy_Lady

I spent two weeks boon docking in January in Quartszite and had trouble keeping my batteries charged with my generator. Here are the specs.

2 Trojan T-105 batteries (less than 1 year old and attached to shore power when

not camping.

New Honda 2200EUi generator. (less than 10 hours of use)

WFCO 55A Power Converter (Model 9855)

I have a Dometic CFX65 compressor refrigerator that is supposed to draw 8.2 amps. I choose this fridge because of its supposedly low power draw. This was the main 12v use as well as sometimes charging my phone and tablet.

My only previous boondocking was for no more than 3 days and I usually had to run the generator on Day 2 for 2 hours to bring up the charge.

In Quartszite after about Day 3 I couldn't seem to keep my batteries charged to a sufficient level. I decided to record the battery readings.

After 3 hours on the generator 13.62
Unplugged from generator: 12.85
3 hours after charge 12.65
7 hours after charge 12.29
overnight/next morning 12.32

With this discharge rate I had to run the generator everyday, sometimes once in the morning and then again in the evening if I wanted to turn on any LED lights as well as charge my phone or tablet.

My guess was that the fridge was drawing way more power than the stated specs. I could see it drop down to 12.36 when the compressor kicked on 3 hours after the generator charge. The compressor usually only ran for about 90 seconds every 3 hours during the day. The temperature dropped pretty quick after sunset and I rarely heard it kick on in the evening.

When I got home I decided to run an experiment. I cooled the empty fridge on shore power down to the same temp I had set in Quartszite. In Quartszite nights were in the high 30s low 40s, days between 58 and 70. I couldn't exactly replicate the day time temperature (highs in the mid 50s) but the nights were the same. Also the fridge was empty so it would have to run more to cool. I unplugged from shore power. Here are the numbers:

Fridge cooled, shore power. 13.08
24 hours later 12.72
48 hours later 12.71
72 hours later 12.45

So, after 72 hours following a shore power charge the number was higher than after 24 hours from a generator charge. Also, I was not using EcoThrottle on the generator.

Any ideas?

I am sure no expert. I have not dry camp except for short periods of time (1 day). I have a 2018 27’ Intl Sig with FB. I have been told by an expert Airstream puts in too small a converter/charger (55amp), also the 9855. Last month my converter died, I replaced it with a Boondocker 1255 CL, also a 55amp. It happened to be defective so Company replaced it but I asked for their 65amp. All is well now and no other problems, except for my auto awning, but don’t get me started on that! It’s a whole other story!

[Milo1952]

Originally Posted by RJKSr

If your converter/charger is similar to the one they install in newer Airstreams, I suspect that is the issue. Our 2017 came with the a Parallax 5355 and two 12V Interstate 75AH batteries. We too experienced poor charging with the generator because it used the Parallax 5355 when plugging the trailer into the generator. I discovered that the Parallax max charge was 13.2V, which is OK for maintaining a float charge, but cannot provide an adequate charge to batteries that are close to a 50% discharge.

Parallax engineers said this was to prevent "boiling" batteries dry and suggested installing their Tempassure 4400TAU unit which allows a higher charge rate because it provides temperature compensation. After installing it, I can get +14V with it ... sometimes.

then installed solar which helped because it can charge above 14V in full sun. Later installed two 6V 120AH batteries in series because the Interstates would not last 2 days while boondocking in cloudy weather. That gave us 45 more AHs. The real solution is to change out the Parallax unit with on that has a true multistage charger. For now, we are going to use the 6V batteries for more of their lifetime and then change out the charger to one that can also do Lithium so we can move to higher capacity and better performing Lithium batteries.

I too have the parallax 5355. I want to upgrade to 2 Battleborn Low Temp Lifepo batteries ( yes, they will be out soon)., upgrade the charger to what ?? Add a Victrom BMV-712 and purchase a Zamp 230 Watt solar suitcase, I would also like to ad a 50a-50a alternator charger to my tow vehicle. Most of my charging needs should be taken care of while moving from point A to B.
I also travel with a Champion 3400 watt dual fuel genny. Any suggestions for a lithium charger upgrade and 50a-50a alternator charger would be greatly appreciated. Have any of you done this or something similar ? Brand, model #'s appreciated.
Thanks Harry

[HRTKD]

It's threads like this that make me doubt my sanity. The info posted by AirMiles was very good.

Like the OP, I have dual Trojan T-105 6v batteries. The original converter I had in my trailer was doing a poor job of getting the batteries charged. I have a single solar panel on top of my trailer. Because of that, I rarely need the generator to run. But when I do, it's because I need the microwave or the AC to run, or my 12v draw has been significant. I have a propane/electric refrigerator, which I consider superior for boondocking.

I replaced the OEM converter (no idea what it was) with one from IOTA Engineering, the DLS-45/IQ. It was a direct fit and had been recommended by a fellow RV'er that I trust.

Because of what was posted in this thread I had to go lookup the specs on my converter (doubting my sanity for having purchased a converter that nobody mentioned). After much digging I found the charge specs which says that it will charge at 14.8 during the bulk mode. It's a 4 stage charge. The equalization stage is designed to avoid sulfation. However, I doubt that my generator is in use long enough to get to that stage. Because of that I think I need to pull my batteries once a year and put them on a 4 stage charger here at home. Hopefully my CTEK MUS 4.3 will do the job.

[jimdelane]

Trojan T-105 are GC2 batteries. Trojan, Lifeline and Rolls are top of the line in lead acid. Properly maintained and gently used, they will last years.

The listed amp hour capacity depends on your amp draw due to something called Peukert's law.
At 37A draw - the capacity is 185Ah
At 20.7A draw the capacity is 207Ah
At 11.25A draw the capacity is 225Ah
At 2.5A draw the capacity is 250Ah

Energy is quantified by watts. WattHours = nominal voltage x AmpHours. Lead acid batteries are 12 volt nominal. So 225Ah x 12v = 2700 Wh
The 12.12 rule states that if you see 12.12 volts - you are at 50%. You never saw below 12.45 so you probably only had about 40% discharge over 3 days. You had used up 90Ah or 1080Wh.
You used about 30Ah or 360Wh per day. That is not bad.

Per Trojan Technology Info page - "For optimum life and performance, we generally recommend a discharge of 20 to 50% of the battery's rated capacity even though the battery is capable of being cycled to 80%." Trojan does not recommend 80% discharge if you want the battery to last. No lead acid battery should be discharged over 50% or you will be buying new batteries sooner than you expect. Besides, you really do not be wanting to run you fridge and stuff on 11.6-11.75 volts which is what you see at 80% discharged.

20% of 225Ah @ 11.25A = 45 usable amp hours or 540Wh
50% of 225Ah @ 11.25A = 112.5 usable amp hour or 1350 Wh.
T-105 are 6 volt so you need (2) batteries = 12v @ 1350Wh.

Per Trojan Technology Info page - "Trojan batteries self-discharge approximately 4% per week" So you lose 9Ah (108Wh) boondocking each week or 1.29Ah (15.5Wh) per day from self discharge.

On the other side of the coin, the charger / lead acid battery is inefficient. The charger is 13.8v at 10A which produces 138 watts of energy. Lead acid batteries have, at best, 85% charge efficiency as you lose 15% in the chemical energy conversion process. Older batteries are less efficient. So in the end, you get 117 watts of energy from the charger per hour.

All these numbers are great, so throw into the mix that you probably have a smart charger so you do not overcharge the batteries. The charger will trottle down the voltage and amps going into the battery as the internal voltage (charge) goes up. The bulk charge is greater than the absorption charge which is greater than the float charge. Bulk charge ends at around 80%. Since you discharged 40% (60% capacity), you got max bulk charge for 45Ah (540Wh) of the used capacity and a reduced absorption voltage/amp charge for the remaining 20%. In this case, the absorption charge would take longer than the bulk.

In short, based on your current usage you have enough battery energy to boondock for around 4 or 5 days before you drop below 50% capacity.

You have lots of solutions.

1. Upgrade to a Progressive Dynamics charger like AirMiles recommends. You still pay for lots of gas and the wear/tear/noise of the generator. You still have the lead acid battery charge efficiency issue.

2. Put solar on. 400w to 600 watts will go a long way in addressing your 360Wh per day deficeit. You still have the lead acid battery charge efficiency issue.

3. Go with Lithium batteries. You do not have to drop 3 grand for the batteries, charger, monitors, etc. BattleBorn is the brand most people recognize but you have others such as AMPS, Renogy and ReLion which are less expensive and just as good.

The question is what do you want in a battery bank.
Lithium batteries have higher constant voltage throughout discharge cycle, 8 to 20 years life, no maintenance, higher discharge capacity, faster charging, light weight.

Lead acid batteries drop voltage relative to discharge cycle, 3 to 6 years life, constant mainenance and corrosion, limited discharge capacity, slower charging, heavy.

One 105Ah battery has 1344 watt hours @ 12.8v nominal versus (2) T-105 at 1350 Wh at 12v nominal. A battery bank of (2) lithium batteries has twice the energy of (2) T-105 batteries.
A lithium Battery has 12.8v @ 50% charge, a Trojan has 12.12v @ 50% charge. Lithium batteries can be safely discharged to 100%. Trojan does not recommend discharge over 50%.

You can double your energy capacity for around $1500 or keep the current amount for under $1000.

AMPS 105Ah battery 2 @ $675 ea = $1370
https://lithiummarinebattery.com/sho...ithium-battery

Progressive Dynamics PD9130LV 30A lithium power center/charger $157.34
https://www.google.com/shopping/prod...0aAt-TEALw_wcB

Lithium batteries are 12.8v nominal. That means that most of the time, you will see voltage over 12.8V, usually 13V+. At 50% discharge you still see 12.8V.

One 105Ah battery has 1344 watt hours vs 1350 watt hours versus (2) T-105 at 1350 Wh. A lithium Battery has 12.8v @ 50% charge, a Trojan has 12.12v @ 50% charge. Lithium batteries can be safely discharged to 100%.

Lithium batteries charge faster. Lithium chargers produce constant volts/constant amps. A 105Ah battery recommended charge is 14.6v at 30A (438watt) continuous but can take up to 100A charge. The charge efficiency is 99.5% so there is no charge loss. That translates into less solar needed and less fuel costs/wear on the generator.

The cycle life of LFP lithium batteries is 3000 to 5000 cycles.
That means if you discharged the battery 100%, every day, you will get over 8 years. 50%, every day, you would get over 16 years.
Current cycle life standards for lithium batteries is 75%. That means when the battery holds 75% of original charge capacity. That means if you discharged the battery 100%, every day, it will last 8.2 years and you will have a battery capacity of 75% or 78.75Ah (1000Wh).
The cycle life of Trojans T-105 is max 1000 cycles. Current cycle life standards of lead acid batteries is 50%. That means when the battery holds 50% of original charge capacity.
That means if you discharged the battery 100%, every day, it will last 2 years and 9 months and you will have a battery capacity of 56.25Ah (675Wh).

Lithium batteries are maintenance free. They can be mounted in any orientation. They can be placed in a sealed environment as, unlike flooded, AGM and Gel batteries, they do not produce hydrogen gas. You do not have to worry about corrosion build up at the terminals or corrosive/explosive gases.

Lithium batteries are cost effective. Lead acid batteries are cheap. Then figure how much a generator costs. The more you run it the sooner you replace it. Add the gasoline, spark plugs, oil and maintenance costs. Figure the additional solar that you need to address the charge inefficiencies. With lithium and solar you can reduce and sometimes eliminate the use of the generator. The batteries pay for themselves every day.

Lithium batteries have a self discharge rate of less than 5% per month. Lead acids must be used and maintained or they die. Lithiums are more tolerant.

A 105Ah battery weighs 30lbs. You burn fuel for every pound you haul around.

Batteries are an investment in the energy you need to live. You get what you pay for.

[AirMiles]

Great post Jimdelane! That pretty much sums up the GC2 vs Lithium decision.

I bought the cheap GC2 solution and can live on the 180AH they produce by discharging them down to 20% SOC (state of charge) as needed. I understand they won't last as long with my deep discharges, but justify the shorter life because they are cheap. I've abused my GC2 batteries for over two years, including 242 nights of deep draw downs so far, and they still perform and test as new. That's about $1 per night of use to date which continues to drop with each additional night.

[OTRA15]

Originally Posted by jimdelane

. . .
Batteries are an investment in the energy you need to live. You get what you pay for.

Thank you for your extensive summary of battery options in Post #38.

Peter