Generator vs. Shoreline charging times…

[Wyatt]

This past weekend we were off the grid, we’ll sort of.

Overnight, we ran a bank of 4 LifePro 100amp battery bank down to a 54% SOC over a 12 hour period using a lot of stuff.

Start the generator and 5.5 hours later I’m still only at 74% SOC.

Managed to run the shoreline cord over to a house and in the next 3 hours they were at 100%.

Thoughts on why the generator appears to be charging the battery bank more slowly then when on shoreline, or even why it seems to take so long at all?
Thanks!

[DavidM]

It should take exactly the same time to charge from the RV's charger whether it is powered from the generator or a shorepower line. All I can think of is that when you hooked up the shorepower line, you reduced some of the big loads on your RV letting it charge faster.

David

[Morich]

I think it is all as it should beand point out some of the things that are hard to get folks to believe!
One of the first things to note is that battery charging is not a quick process,so connecting to an alternator rated for 125 amp or a converter rated at 50 amps will NOT change the amount of time it takes all that much for simple reasons. It takes TIME!

The rated output of any charging system is how much current that system can put out without danger of overheating, not what it DOES put out with any given cable and battery setup. What controls how much current a charge system can put into a battery is the voltage if we keep the resistance the same. Since we don't want to up the voltage enough to burn out things like lights that are on the battery system, we have to stay around 12-14 volts and since the resistance is still going into the same cables and batteries whether we use a 125 or 65 amp rated charger is not making much difference.

Current is the voltage divided by the resistance, so if the resistance stays the same and all we can vary is the voltage in a small range, we really can't shove much more current into the battery by using a higher rated charger once we are using a charger which DOES put out the maximum current the batttery can safely handle. If we can charge a battery at ten amps maz, there is nothing to be gained by using a charge systems that maxs at 125 versus 65.

But the time is not so much a factor of whther we are using generator to power the RVconverter or if we are using shore power to feed that same converter. Same converter does the same thing, no matter where it gets it's power!

But the timing can certainly fool us really easy whenn we look at the time it takes to get from one state of charge to another as that is not a straight line going from 50% to 75 % versus 75% to 100%.

Copied this:
Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points.

That needs some thought for a clear picture of why charging gets confused.
When we charge a battery that starts at 10 volts, using a charger outputting 14 volts, the difference at the start of the charging is 4 volts across the two points as mentioned above. If we plug those numbers into Ohm's Law we get current= 4 divided by the restance X. (I = 4/X)

But when the battery gets partly charged the voltage will have increased, so lets say it now reads 11 volts instead of 10? The difference between the two points, charge and battery will now only be 3 volts and that changes how much current flows!
I= 4/ X gets you more current that I=3/ X !!

And as the battery gets closer and closer to fully charged, the current drops and we can continue to see the reason for that drop if we set up more formulas to compare.
When we get into the voltage difference being 1, .5, or. 1 volts, the current continues to decrease dramatically! Plug in any theoretical number for resistance and the numbers may make more sense. I like 10 as an easy one to use!
The better charge systems will also drop off the rate of charge as the battery reaches full charge.
So your question was why did it appear that the convertor worked different when on generator than shore power?

I might also assume there was some difference in the amount of power being used in the RV at different times. That power comes out of the batteries and it may be things that we may miss. Weird things can sneak up like opening the frig, plugging in a cell phone, leaving the steps out so the light is burning, or some odd thing we don't spot???

For why it takes so long, I can only say it is the chemicals involved and it takes time to get them back in order. That is one of the big challenges and reasons for all the work being done on newer battery designs. Lithium works faster than lead and the even newer solid state batteries are making the lithium look "old school".

This is a site with chart info that I like for showing how long and slow lead acid batteries take and it comes out showing a good charge may take 9 hours or more!
https://batteryuniversity.com/articl...ead-acid%C2%A0

The big point is that folks who are sure they charged their batteries in less than an hour are missing something or doing something the industry would really pay a lot to know about!
I'm betting on a bit of confusion involved!

[DavidM]

One interpretation of Morich's remarks above, is that the OP just thought he was at 54, 74 and 100% charged. How did he know? If it was from voltage readings, they are notoriously inaccurate as an indicator of state of charge.

The only way to know is to start with a known SOC, ie flat dead and measure the amp hours it takes to reach a certain point. This can only be done with a shunt-based battery monitor. Every owner of LFP batteries should install one to really know what is going on.

David

[Wyatt]

Thanks for all of the responses. I have a Victron battery display so I know exactly how much the true SOC is—what’s going in and what’s going out. I should have taken screen shots at more intervals.

But I think you’re also all right. When we were on the generator we were still using power—more than when we went to plug in, as we left the RV during that time. Interesting how the daytime use drain slowed the charging process down so much.

So you’ve all confirmed I’m not crazy, and that what I assumed—shoreline and generator charging should be equal, the third factor—day use—was the variable, and I thank you all for the time to give me some peace of mind.

I am a little surprised, that to put 200 amp hours back into the batteries could take 7 or more hours of generator charging a day.

How did we use 200 ah in such a short time? We were hosting people at the RV all for our daughters wedding. I’d imagine the draw would be less in normal off grid experiences…

[DavidM]

Charging at 30 amps on average is not surprising if you have the standard converter. If you haven't done so, consider upgrading to a Li specific converter. Progressive Dynamics has their lithium specific series of chargers, the PD91XXL.

David

[lenore]

Agree with DavidM that would have been my question is do you have a Lithium specific converter. I switch my original converter out and when the LIPO battery is down it charges quite fast when hooked to converter. Mine puts out 50Amps, but in when it charges stays at a higher charge rate longer, something the non LIPO charger does not do.

[Morich]

Yes, the difference in Lithum was not a point I considered and it does work much quicker than lead/acid. Ignore the charts, I referred to as they are for lead acid.

I'm really looking forward to the newer solid state batteries as they come online as a way to move much further away from gas powered cars. I'm reading about full recharge in fifteen minutes on them but they are just begining to come out. Bet they are super pricey right now!

https://www.torquenews.com/15475/fir...as-wh-kg-ratio

[creativepart]

Originally Posted by Morich

I'm really looking forward to the newer solid state batteries as they come online as a way to move much further away from gas powered cars. I'm reading about full recharge in fifteen minutes on them but they are just begining to come out. Bet they are super pricey right now!

Those may be the first “commercially viable” solid state Lithium’s that have been announced BUT they are not available right now and are a number of years away from being what will no doubt be super pricey batteries.

Solid state batteries are at a proof of concept stage and are simply working out the details and funding for proposed future manufacture.

Our current Lithium Iron Phosphate batteries of today were at this stage in 1996 - so it’s likely to be awhile for solid state batteries to be commercially available.

[Wyatt]

Originally Posted by lenore

Agree with DavidM that would have been my question is do you have a Lithium specific converter. I switch my original converter out and when the LIPO battery is down it charges quite fast when hooked to converter. Mine puts out 50Amps, but in when it charges stays at a higher charge rate longer, something the non LIPO charger does not do.

Hi David and Lenore,

I have the WFCO charger/converter that came with my 2018 unit, but I swapped out the charger board that WFCO specifically makes for lithium. Today, when I charge them, I’ll check and see how many amps it’s drawing. Thanks!

[Wyatt]

I had a LOT of answers to my questions today…

My RV was in the street, as we came home from our trip on Sunday, and I was doing some roof maintenance, (my driveway is unsafe to get on the roof as the ladder is leaning downhill).

The batteries had run down to ~57% over those past two days (we have two 100v refrigerators).

I started the Onan 4000 generator and had ~50 amps coming into the batteries via my WFCO Charger/converter with the lithium upgrade charging board—as registered on my Victron.

When I started the engine,WITH THE GENERATOR STILL RUNNING, the amps going into the batteries jumped to ~140 amps.

With just the engine running, the amps into the batteries was ~107 amps.

When I plugged into shoreline, I had the same ~50 amp charging profile as the generator.

I called Battle Born, and shared my numbers. They said they all sounded great, as that is what they would expect to see.

My alternator on my F53 max output is 175 amps.

The WFCO charger/converter passes through ~ 50 amps.

So when on both, I got ~145 amps into the 100 amp Battle Borns.

Here’s what Battle Born said:

50 amps per 100 amp battery is appropriate. (So I’m within those limits). They said 50 amps of charge per 100 amp battery is what they want to see it max out at.

When asked if THEIR batteries should be stored at less than 100 SOC, he said NO. He empathically stated that their batteries COULD AND SHOULD be stored at 100%, and charged to that frequently and that storing them at less than 100% DOES NOT change the life expectancy of their batteries AT ALL.

He went on to state that, “A lot of what you are reading online can be misleading. It simply does not apply to OUR BATTERIES, but MAY apply to other brands with different technologies”.

When I asked him if my 175 amp alternator needed ANY PROTECTION against overheating, he said again, “it’s a robust alternator, and it’s doing EXACTLY what is should be doing, you’re well within your limits, and that which the batteries and alternator can withstand”.

Interesting… Thanks again for all the input.