Energy management

[Mike8253]

Remember also that your TV's, while turned off, will still be drawing on your batteries. When I'm camping with no hook-ups, I always flip the Entertainment circuit breaker off. That will kill your TV and DVD/Surround Sound system draws until you actually want to use them.

[FlNewmarBob]

There is a lot of mixing of points here. First, the refer runs on 120 VAC and probably averages 3 to 4 amps…..which equates to about 30 to 40 amps at 12 VDC. The inverter has about 92% efficiency contributing to consumption. Then there is all that parasitic drain….USB jacks, DC lights, fans,….you name it. Things like how often and long you open the fridge, ice maker on…..and so on.

Now the battery thing. Are you reading the battery voltage while under load or with DC diconnected and batteries rested….even 30 minutes will give a more accurate voltage, thus charge level. The 50% charge factor is the nature of Lead acid batteries….take charge levels below 50% and you are killing the batteries….not going to get into the science here. Just be aware, 12.3 VDC rested is considered 50% by the batteries industry. Under load, depending on load amount you may see 12 or 11.9 VDC and that would be about 50%.

Suffice to say this is truly more complex than the RV MFGs want you to know.

Lead acid batteries (including weaned AGMs) are very reliable when operated within their designed parameters. Go astray and you end up with warm food and dead batteries. There are too many variables to address this here. Feel free to PM me and I will continue the discussion….BTW, I am an electrical and DC power engineer….

[Mark_K5LXP]

Originally Posted by FlNewmarBob

….take charge levels below 50% and you are killing the batteries….not going to get into the science here.

I'd love to see the science. It would be interesting to see what all the battery manufacturers are getting wrong. Please provide links.

Mark B.
Albuquerque, NM

[pameridan04]

Originally Posted by rrlowen

The batteries are 4-6volt @ 225 each which would give a usable 225 AH (1/2 of the 450AH) at 12 volts.
I think my original post was misleading. The problem is that the batteries are discharged after a few hours while dry camping. I thought that the coach should last overnight if the batteries are fully charged. The only significant draw would be the fridge. If the fridge draws 10amps @ 12 volts per hour (running half time) that should only use 100 AH over a 10 hour period. Add in another 10 AH over that time for miscellaneous draws and there should be no problem sitting overnight. As some have suggested, there is a problem here. Time to check the batteries and run a series of energy draw tests.
Thanks for the information which confirms what we had thought.

We just dry camped for two days with our 2021 Red 33AA. I usually run my generator about 30 minutes before bed. They will charge to approximately 13.3 while jenny is running. They drop to about 12.7 right before bed. Overnight I will have Fridge running on inverter, 4 TV's off but red lights drawing power, WIFI Ranger drawing power, MY Cpap machine running all night, and even my bedroom ceiling fan running on low. In morning my batteries are low about 12.0 or 11.9. Run generator for about an hour and I am good to go again.

With your batteries low say at 12.1 or 12.2 you should be getting solar power charge if it is a bright sunny day. I have yet to experience this with my three solar panels on roof. Still playing around with controller.

Jim P.

[Sbrownstein]

Originally Posted by pameridan04

We just dry camped for two days with our 2021 Red 33AA. I usually run my generator about 30 minutes before bed. They will charge to approximately 13.3 while jenny is running. They drop to about 12.7 right before bed. Overnight I will have Fridge running on inverter, 4 TV's off but red lights drawing power, WIFI Ranger drawing power, MY Cpap machine running all night, and even my bedroom ceiling fan running on low. In morning my batteries are low about 12.0 or 11.9. Run generator for about an hour and I am good to go again.

Jim P.

Do you have an SOC meter? In my experience, with an identical house bank as yours, there is no way to get anywhere close to 90% SOC from 50% with only an hour of generator time. I have a 60 amp converter and manually set it to "boost" charge with its charge wizard. Now, Forest River didn't give me really good copper between the converter and the house bank.

[FlyLab]

Originally Posted by rrlowen

The batteries are 4-6volt @ 225 each which would give a usable 225 AH (1/2 of the 450AH) at 12 volts.
I think my original post was misleading. The problem is that the batteries are discharged after a few hours while dry camping. I thought that the coach should last overnight if the batteries are fully charged. The only significant draw would be the fridge. If the fridge draws 10amps @ 12 volts per hour (running half time) that should only use 100 AH over a 10 hour period. Add in another 10 AH over that time for miscellaneous draws and there should be no problem sitting overnight. As some have suggested, there is a problem here. Time to check the batteries and run a series of energy draw tests.
Thanks for the information which confirms what we had thought.

Right, never go below 50% total capacity with any lead-acid battery, or you really start to degrade its useful life and its ability to accept a charge. Your alternator probably puts about ~150 watts into the house batteries AFTER the engine batteries are done being recharged while driving. Your residential refrigerator probably uses about ~140 watts while running, but it only runs probably a bit less than half the time. Check your 12v fuses in the basement under the driver, some of those run the battery combiner emergency-start solenoid which also lets engine charge house batteries. To help you learn your system, and troubleshoot any issues, get 3 things: Kill-A-Watt device, volt meter, and install a Victron BMV-712 with the Smart Shunt in your RV.

The Kill-A-Watt will show you current energy usage, as well as average usage over time. Leave your refrigerator plugged into it for a week and see how many watts (or Amp-Hours) it uses. You can also plug your shore power into it and see exactly how much juice your RV is taking from a 15-amp connection. It answers questions like "if I turn on the 1000watt curling iron, am I going to blow a shorepower breaker?"

The Victron device will be the best game-changer to help you know your exact USABLE power capacity status, charge/discharge rate, and how many hours you can go at your current discharge rate. SOOO much better than the low/medium/high "idiot" lights for battery status that you currently have. With this, you can confirm the juice coming INTO your batteries from solar. Turn the engine on and watch the number jump. Turn the generator on and watch the number jump A LOT.

Keep in mind, your inverter/charger will only use about 1200-watts (100 amps at 12v) to charge the batteries (charger limitation) even though your generator might be 8000-watts.

[twinboat]

Lots of 50% DOD myth believers.

Still waiting for some science.

[woofus]

and install a Victron BMV-712 with the Smart Shunt in your RV.


The Victron device will be the best game-changer to help you know your exact USABLE power capacity status, charge/discharge rate, and how many hours you can go at your current discharge rate. SOOO much better than the low/medium/high "idiot" lights for battery status that you currently have. With this, you can confirm the juice coming INTO your batteries from solar. Turn the engine on and watch the number jump. Turn the generator on and watch the number jump A LOT.

X2... using the Victron, I learned that the battery voltage on the Spyder is not accurate and I had to change parameters so that the inverter would not shut down when brewing coffee in the AM, as the Spyder thought the battery bank was low. I have also learned that I can turn off the DC charger if plugged into shore power as my 980W of solar recharges the daily 12 V load. Still have to learn more about true boon docking, but the Victron is essential.

NOT TRYING hard to conserve, I will use about 200-250 A-Hr ( of my 900A-hr battery bank) overnight. But I haven't needed to run the generator to recharge batteries yet. On my previous coach with 2x 6V 225A-Hr batteries, I was running the gen 2 hrs in the AM and 2 hrs in the PM but couldn't fully charge after the charge rate dropped into float. Solar fixes that.

[Mark_K5LXP]

Originally Posted by twinboat

Lots of 50% DOD myth believers. Still waiting for some science.

[Insert Jeopardy thinking music here...]

Mark B.
Albuquerque, NM

[FlNewmarBob]

See links at end......

There are many possible scenarios as to the path to either good or bad battery longevity. Issues include total depth of discharge (below 50%), the rate of discharge (load amount over time...short or long), temperature, charge rate....could go on for pages.

The Federal document example shows DOD vs impact on cycles. Understand a low load/long discharge to above the 50% rate is easier on the batteries. Note a discharge to 50% is considered one cycle.

Hitting the batteries hard with high discharge rates generates heat. Charging batteries with large chargers generates heat. Heat is the enemy of batteries.
Chargers with multi-stage charge profiles help manage some of this by pushing hard at first, stepping back and then maintaining (trickle). Lead acid batteries take a charge pretty easily up to about 85% then it's a slow climb (and hard on the batteries) to the top....thus the throttle back.

The real issue here beyond the understanding and application of good practices is the RV industry's stupidity in putting all this "high draw" stuff in (Refer, microwave, outlet for the hair dryer,....and on) and not enough DC battery plant to reasonably sustain operations within the parameters (and capacities) of the batteries. Fact is I still cant believe any RV manufacture is still putting wet lead acid batteries in any coach. Owners don't maintain them. Fact is well maintained and non-abused wet cells will give years of service. Too little and/or no maintenance will result in the "batteries every 2 years" syndrome.

Back to the math....easy version. It's about watts. The typical residential Refer draws an average (over a 24 hour period) of 8600 watts (some more some less). A battery plant with 450 amps X .5 (50%) X 12.4 volts = about 2800 watts..... thus about 3 hours..... maybe an hour or so more if you keep the fridge door closed. (as an aside, a 3/4 full fridge and freezer once cold is more efficient than an empty one......more cold mass = less demand on the cooling system.....ice and freezer packs work great). Forgot one thing...inverters eat 5 to 10% of your battery capacity (efficiency factor).

Fact is most of these coaches are not designed to "dry camp" with the basic, factory installed DC plants. There is enough there to hold you over "stop to stop", while setting up and maybe a little more. They are counting on the engine alternator to keep the DC side up while driving and generator or land power while parked.

Again, private PM if you wish to "deep dive" this issue......

Here ends the lesson....(maybe some rant)...


https://federalbatteries.com.au/news...t-so-important

https://www.eastpennmanufacturing.co...chure-0273.pdf

[sibe]

I did the math on a 18cu samsung, popular RV and I have one in my kitchen.. Tag says it can use avg 1628 watts per day, 13.56 amps , 130-140 AHR at 12vdc..


My old winnie is older ammonia .. 270 watt element.. I have it on Inverter right now.. 28.3 amps 12v, the propane detector is on, TV standby, microwave clock and air freshner..
I turn off fridge the draw is around 3.1 amps drops to 2.8....
Any way, I can Get 10Hrs out of my 300AH acid batteries, once fridge gets cold it cycles..
If I pre chill the fridge and food then run it on Batteries, 14-16 hours is no issue.
Batterys will be at 11.8ish at that point.. depends if I put TV on LOL..

My point here is just to show some actual use ...

Now I have 400 watts solar, it on a perfect day, parked perfect will dump 18-20 Ahr back in .. In a 10 hour day,, i have reset to 0 the AH counter, left fridge running after batteries on a full charge,, 8am start, 6pm I checked AH made, 130ish.. batteries at 78-80% or so.. It was mid summer 80 degrees .. so it was warmer inside, fridge was working..

the 400 watts solar is not enough but I have used propane from 8am to 9 pm the run batteries all nite with TV etc, and fridge on inverter.. Then I get batteries to 90-95% ..

I do run them down to 35-45% many many times.. NO issues, I change them every 3-4 years,, If I camped more that 10-16 weekends I would have way better battery bank and more solar.. Actually I have another 200 watts on order.. that should give me 25-28 Ahr on a good day..

[Shadowrip]

Originally Posted by twinboat

You may have dealer killed batteries. They let them die and sit on the lot.

Never saw if this was checked... mine was doing the same thing, ref off after 4 hours. Both house batteries reading 12v.
Did a load battery test, one had a bad cell. Replaced both, ref runs all night now.
Coach was 6mo old .

[Mark_K5LXP]

There are many possible scenarios as to the path to either good or bad battery longevity.

What is the definition of "longevity" -?

The Federal document example shows DOD vs impact on cycles.

All the manufacturer data sheets show cycle life graphs. What runs stuff though is Ah delivered to the load, not cycles. When you apply Ah delivered vs cycles you discover the "impact" of DOD doesn't have quite the deleterious effect many consider it to be.

Understand a low load/long discharge to above the 50% rate is easier on the batteries.

Peukert effect is a separate discussion and independent of DOD, "50%" has no bearing with Peukert.

Hitting the batteries hard with high discharge rates generates heat. Charging batteries with large chargers generates heat. Heat is the enemy of batteries.

Heat is not the contributing factor in terms of charge efficiency. It's the gradient of conversion and rate of diffusion across the grid and paste that if the rate is exceeded the structure is damaged and capacity is lost. Heat causes reactions in general to happen faster and does cause a reduction in service life if operated at elevated temperatures for extended periods overall but is separate from extreme elevated current or voltage charge and discharge degradation.

the RV industry's stupidity in putting all this "high draw" stuff in (Refer, microwave, outlet for the hair dryer,....and on) and not enough DC battery plant to reasonably sustain operations within the parameters (and capacities) of the batteries.

100% agreement. Then compound that with marginal charge equipment (though multistage has been a big improvement), and the lack of any meaningful capacity or battery management and you have a formula for user disappointment.

I still cant believe any RV manufacture is still putting wet lead acid batteries in any coach.

They last long enough to get them off the lot.

Too little and/or no maintenance will result in the "batteries every 2 years" syndrome.

Sounds like a recurring service revenue opportunity to me...

most of these coaches are not designed to "dry camp" with the basic, factory installed DC plants.

In a perfect world it would be a customer option at time of sale. Some dealers offer that along with solar, though at a premium. Guessing that a good number of customers don't know an amp hour from a happy hour and have no idea what they would want or need if it was offered. A hands off BMS adds cost to a price driven product, so push them out the door and have a nice day.

Again, private PM if you wish to "deep dive" this issue

I like it right here, need to dispel this 50% rule BS in public. Neither one of the linked documents has any factual data nor discusses delivered amp hours or service life. Again, cycles don't run your stuff, Ah do. The long and short of it is if you crunch the data you discover that across the entire range of 0% to 80% DOD (0% to 100% Ah) the service life difference is less than 10% best to worst. The "50%" point may not be 50% depending on the battery, in the case of the T105 the peak service life occurs at 30%. The delta in service life between 50% DOD and 80% DOD for the T105 is about 3%. So all of this anguish about "killing" your battery by going below 50% is all for the sake of a few percent potential service life. Factor in that at lower DOD you cannot practically cycle a battery often enough to utilize it's capacity. You end up recycling the battery before it's useful life is realized and all of this conservation is a net loss when it ultimately expires. There are logistical reasons to pick a given DOD point and that's fine, but battery longevity in this application isn't one of them.

Mark B.
Albuquerque, NM

[Sbrownstein]

Originally Posted by Mark_K5LXP

What is the definition of "longevity" -? ...Mark B.Albuquerque, NM

Generally agree. Most coaches are designed for "average use." This generally means connected to shore power in an RV park. The additional cost for significant "boondocking" just cannot be rationalized on each and every coach. I think that Georgetown did a decent job optimizing cost/performance on my coach. It came with a residential reefer, 4 deep cycle batteries, a 2000 watt pure sine wave inverter and a 70 amp PD converter. If I have any objections to what they included they would add maybe $250 to the manufactured cost. They could have:
1) Included some sort of SOC meter to the standard offering.
2) Wired the converter with heavier gauge wire to the battery bank (currently #8) and shortened the distance to the bank from the current 20 feet to much less. The current path means I never see more than 40 amps charge current and that for only a few short minutes.

Otherwise the rest is up to the buyer.