Help Me Understand the Relationship Between Lithium, Shore and Inverter

[Sky King76]

So when I plug this B class in to 30Amp shore power,  does the shore power charge the batteries and the batteries are running everything either as 12V or through the inverter? Planning our first RV experience for next week and I’m still trying to understand the details here. I went out yesterday and turned on power to the 200Ah batteries, then the inverter, then the A\C and wow…it was pulling 76Amps. So how does that work? If we’re connected to 30Amp shore does the batteries supply the rest of the 46Amps or what? Otherwise, wouldn’t the shore breaker pop?

Sorry…just trying to avoid as many “surprises” as possible on our first adventure.

[Chalkie]

I question how you came up with 76 amps. I am currently running two a/c's with fans, TV and some miscellaneous electronics running and am only using 29 amps. Yes, I am on 50 amps but 30 amp RVs generally only have one a/c but you get the idea.

In a normal scenario when you are plugged into shore power everything that runs on 120/240 volts is getting its electricity from the shore. Your rig also will have a convertor which charges the batteries. If you need to run say a residential refrigerator while you are not connected to shore power then you would have an inverter which takes 12v from the batteries in and outputs 120v/60Hz electricity to run it. 

You can also mix solar panels into all this put since I do not have solar I can not comment.

[Sky King76]

Thanks Chalkie… 76Amps, 12.6 volts was on the MasterVolt. With the inverter on to run the air conditioner it showed 120V and 806 watts. I thought it was extremely high as well and dumbfounded but I’m learning. Bought it end of May with only 3,000 miles so it’s “new” and maybe there’s bugs or the batteries need to cycle more. 

I was just concerned how we can plug in to a 30Amp and see 76Amps draw.

[GlennWest]

806 watts at 120v is 6.7 amps

[Chad Heiser]

The 76 amps you saw were DC amps coming from the battery at 12 volt.  That energy was being inverter-Eddie to AC power through the inverter to power the air conditioner.  If that same air conditioner were being powered from shore power at 120 volts it would be approximately 7.6 amps of A/C (alternating current) power.  It takes approximately 10 times the amps/current at 12 volt (through an inverter) than it would require at 120 volt (shore power) to power the same A/C appliance.

When you are plugged into shore power, that power is distributed to all your A/C loads as needed.  When you don’t have shore power, you turn the inverter on and it draws 12 volt power from the batteries and inverts it to 120 volt A/C power to power the same loads.  DC amps will always be approximately 10 times the AC amps (assuming a 12 volt system).

[Sky King76]

Wow…thanks Glenn and Chad…take the rest of the day off…so helpful!!! AND thanks for not writing something sarcastic about how stupid I am. So at 76Amps coming off 2 100 Ah batteries and drawing 75Amps  it would make sense the air conditioner is only good for 2.5 hours or less. 

Our first RV trip will be to Maine in a week to stay with friends who live just outside Acadia National Forest where it’s high 40’s at night and averages low 70’s during the day so air conditioning may not be a big deal. Plus if it’s drawing less than 15Amps of AC power we can connect the shore power to the house and be good to go.

Unfortunately, I’m gonna start looking at replacing these batteries with maybe 2 300Ah. These RV’s can come with up to 940Ah batteries depending on your options so there’s obviously room under there with this being front wheel drive.

 

 

[GlennWest]

food for thought, Mini splits pull far less for same or better cooling. 

[oldjohnt]

Mornin Sky King, congratulations on your rig and I agree with the other fine sparkies, FWIW here's my take and thoughts on your good question.

 When you plug to shore power, it can (depends on your system configuration) power up a Converter/Charger (120 VAC to 13/14+ VDC charging voltage) to charge your battery and your battery can in turn (again depends on your system) feed a 12 VDC to 120 VAC Inverter to run your AC and/or other 120 VAC loads

NOTE in an Inverter: For every amp of supplied 120 VAC, the Inverter will draw around approximately 11 amps from your 12 Volt battery. IE if your 120 VAC AC required lets use say 7 AC  Amps,, your battery would have to pump out 7 x 11 or 77 DC Amps into the Inverter.

While sure you can power an AC using stored battery energy and an adequate rated 12 VDC to 120 VAC Inverter, with ONLY 200 Amp Hours of stored battery energy YOU CANT RUN VERY LONG before the battery is drained.

Typically (depends on configuration) when plugged to shore power IT NOT THE BATTERY/INVERTER would run the AC and also power your Converter/Charger to keep the battery topped off. Then when dry camped with no shore power (depends on configuration) stored battery energy can power the Inverter to run 120 VAC loads. 

 That 76 amps you were reading may have been (cant say not there) the DC amps coming out of your battery to power your inverter to run the AC (Must be a smaller AC load, big rooftop units may be more like 1000 to 1500 watts subject to size ?? while a Mini Split can draw much less).........AT THAT SAME TIME if plugged to shore power (and your AC was running off Battery/Inverter power) your Converter/Charger could also be drawing shore power based on its rating. Maybe say 5 to 24 or so Amps of shore power to charge your battery.

The 76 Amps may be ?? DC Amps what your battery is delivering to the Inverter to run the AC, while the 120 VAC AC Amps is what the Converter/Charger is drawing from shore power, which depends on the size of your Converter/Charger maybe say 5 to 24 amps ??????????

Shore power delivers AC amps to power your Converter/Charge to charge your battery and could also power an AC HOWEVER the AC could be configured to run off shore power when plugged in versus using battery and inverter (less efficent that way). 200 AH of battery isnt going to run an AC very long.

FWIW my preference is to run an AC strictly off shore power (NOT battery/inverter) and of course also run my Converter/Charger to keep my batteries charged up. Using battery and inverter to power an AC is less efficient and not so common for smaller systems such as yours although fine for large systems. With ONLY 200 battery AH running AC isnt real practical, maybe 400 to 800 or MORE AH   PLUS  you need a system like Solar to recharge the batteries. 

Clear as mud Im sure lol post back any questions

John T

Edited June 12, 2023 by oldjohnt

[Sky King76]

Thanks John. I’m gonna contact the guy who did the inspection on an RV that failed and see if he does battery upgrades. We had just looked at a Thor Sequence that was only a year older but had a generator. I did recall seeing a Thor video saying the lithium batteries was an “upgrade” over a generator BUT I missed the part where they were talking about the 800Ah or 940Ah setup NOT the 200Ah, like ours. I guess if we’re going to boondock a lot, batteries are obviously a lot quieter than a generator for neighbors and the like.

What confused me and thus my original question, I was looking at a specific EV car a couple years ago and in my research found the older ones were equipment with a gas engine for when the batteries got low but the engine did NOT run the car, it charged the batteries, which still ran the car. Technically I guess we do have a “generator” of sorts, in that I can start the engine which is equipped with a high output alternator. I know as a kid we’d never let a vehicle idle for a long time but I guess the newer vehicles like the RAM 3500 it’s OK.

We do have solar…190 and I’m gonna go up and look at the space on the roof for more. I read 380 was pretty common, so I should be able to get at least 1 more panel up there.

[Sky King76]

3 hours ago, GlennWest said:

food for thought, Mini splits pull far less for same or better cooling. 

I’ll have to look in to that. I think this one pulls 11,500.

[oldjohnt]

38 minutes ago, Sky King76 said:

I guess we do have a “generator” of sorts, in that I can start the engine which is equipped with a high output alternator

Sky, here's the deal when it comes to an engines alternator being used to charge  RV house batteries.

If BOTH the engine and RV have similar lead acid batteries (common before the days of lithium) the alternator can be used to direct charge BOTH (basically they are connected in parallel while charging both) subject to the alternator and charging system set up.

HOWEVER (A ) if the house batteries are Lithium you CAN NOT direct charge them using the alternator, that can overload the alternator......HOWEVER (B) you can use the alternator to charge Lithium house batteries PROVIDED YOU USE A LITHIUM SUITABLE DC TO DC CHARGER in between which limits the alternator and correctly smart charges your lithiums. Modern trucks can come equipped with a decent sized alternator and onboard inverter for 120 VAC loads, but these are NOT typically super high power units to power huge RV loads.  

PS I believe there are pure EV's,,,,,,,,There are Hybrids that are electric plus have a gas engine,,,,,,,,There are plug in hybrids that have electric plus gas and you can plug in to recharge..I think Im not into all that no warranty

Of course, while you need adequate battery capacity plus a suitable Inverter to run an AC for any extended period, YOU NEED A WAY TO RECHARGE THE BATTERIES when dry camping, be it a Generator orrrrrrrr Solar orrrrrrrrr a DC to DC described above allowing the engines alternator to supply charge.

You have to know the energy the AC and other dry camping loads consumes, how much energy your batteries can store, and your charging capacity to size all of this. Its NOT rocket science but an energy audit is the first step when designing a system. Any solar is good solar but more solar is better lol. Theres like a night n day difference (cost and necessary equipment) in a system that can power ALL EXCEPT AC versus if you need AC when dry camping. Thats Your choice and determination.......plus a hole other thread way too much to cover here in a few paragraphs..

John T  NOT a solar expert see what the other fine sparky gents have to say

Edited June 12, 2023 by oldjohnt

[Sky King76]

Hum…I looked it up and at this point I can’t be specific about the alternator other than it says a “high output auxiliary alternator specifically designed to charge lithium batteries”. I noticed on the bigger battery packs there is a button you can push on the instrument panel so that when electricity gets below 30% the engine will automatically start and charge the batteries back up to 80%.it will do that five times.I would assume that means it’s perfectly acceptable to idol this thing with no problem…

I saw in literature somewhere, something about 170 amp alternator but that may have been on the bigger battery packs or that may be the one I have and there’s even a bigger one. I do have a 3000 watt inverter.

Anyway thanks again for your help John it’s greatly appreciated.

[Sky King76]

So…one other thing. On a positive note from all the help here, is that if the A\C is only pulling roughly 7.6Amps of AC current, then when we visit friends we can easily plug in to their 15-20Amp socket and be good without a beefy 30Amp, as long as we turn the A\C off when running the microwave\convection for example. We don’t use hairdryers or the like so this may work out.

or… Am I missing something here?

[Chalkie]

30 minutes ago, Sky King76 said:

So…one other thing. On a positive note from all the help here, is that if the A\C is only pulling roughly 7.6Amps of AC current, then when we visit friends we can easily plug in to their 15-20Amp socket and be good without a beefy 30Amp, as long as we turn the A\C off when running the microwave\convection for example. We don’t use hairdryers or the like so this may work out.

or… Am I missing something here?

No that should work just fine as long as you are aware of using other things and you seem to be on top of that. I would try to make sure that you are on a 20 amp circuit if at all possible and potentially expect issues if you plug into a GFCI. A GFCI can sometimes interpret the surge when starting a motor (like the a/c) as a fault and trip off.

[oldjohnt]

1 hour ago, Sky King76 said:

if the A\C is only pulling roughly 7.6Amps of AC current, then when we visit friends we can easily plug in to their 15-20Amp socket and be good without a beefy 30Amp, as long as we turn the A\C off when running the microwave\convection for example. We don’t use hairdryers or the like so this may work out.

 FWIW I agree with Chalkies great advice,,,,,,,,,If you're only pulling 7.6 Amps a standard 15 Amp 120 Volt household outlet should work fine SUBJECT TO other loads that may be used by that receptacles branch circuit and their currents ?? SUBJECT TO other loads in the RV which might also be drawing current SUBJECT TO the initial start up current surge of the AC not being so great it would trip the circuit breaker (likely NOT). 

  FWIW I also agree with Chalkie, my preference would be plugged int a full fledged NON GFCI protected 20 Amp receptacle on a 20 Amp branch circuit ALTHOUGH at only 7.6 Amps unless there were other high loads on the circuit a 15 Amp circuit and 15 Amp outlet should work just fine. Of course you can get a 15 to 30 Amp dogbone adapter if the RV has a 30 Amp Plug. If wired to code an outdoor receptacle WOULD BE GFCI but it can still work depending on the RV the AC and other unknowns and variables.

 

2 hours ago, Sky King76 said:

it says a “high output auxiliary alternator specifically designed to charge lithium batteries”.

 I have no idea if that alternator has the capacity, electronics, and proper limitation and regulation to direct charge lithium batteries or not ?? if so it may be fine AS IS. IF NOT you would need a DC to DC charger to prevent alternator damage PLUS correctly charge lithium batteries. From what you say it may be fine?? but I cant say from here. Typically lithium batteries (and their BMS) have a max charging current as wells as a max discharge rating..

 I hesitate to say much more absent your RV and its alternator and electronics specs, consult the manufacturer NOT ME...

 John T NOT any solar expert

 

[Sky King76]

Yep…thanks fellas. I bought a 15-20 to 30Amp dogbone plus an electricity management thing I’d researched that is a surge suppressor AND actively prevents damage. Irony was the dealership had this RV on consignment and they took the goodies out AFTER they took the pictures to post on their website, including this exact surge suppressor. Yes, I called them on it.