Generator Fuel Consumption

[Petervs]

Why all the worry about charging your house batteries back up when they hit 12.2 volts?

Lifeline says 10.5 volt is fully discharged.
From their site:

"As a battery chemically transforms from fully charged to discharged, it's voltage drops from 13.5 - 10.5 volts for a 12 volt battery. As the voltage drops this affects the amount of amps required to drive a load. (Watts law: amps x volts = watts)
13.5 volts x 10.00 amps = 135 watts
10.5 volts x 12.86 amps = 135 watts
As such, this calculator is for sizing purposes only. All systems should be thoroughly tested as they are installed to insure that the battery bank is appropriate for the load on site.

AGM Batteries are not harmed by high amperage charge and discharge so long as the input voltage is carefully regulated.
Charge 12 volt batteries at 13.2 - 14.4 volts


Ratings: Capacity ratings are after 15 cycles and are at 77°F (25°C) to 1.75 volts per cell.

What depth of discharge should be used when sizing a battery?
To get the best cycle life, the average depth of discharge should be as low as possible. Concorde
recommends the average depth of discharge be no greater than 50% of the battery’s 20 hour rating"

There are 6 cells in a 12 volt battery, so 6 times 1.75 is 10.5 volts. This is how they measure capacity. A fully charged battery is 12.6 volts. If you recharge at 12.2 you have used but 45% of the capacity you have paid for.

From the Lifeline site they want the AVERAGE discharge to be 50% which is 12.13 volts, there is no harm in occasionally going as low as 10.5. If we are dry camping I do not worry about it overnight, if it is low in the morning we fire up the generator for a while

I routinely let mine run down to 11 volts before starting the generator if we are dry camping. 12.2 volts is not some kind of drop dead number like that last 1.0 gallon of diesel in the tank.

[Jon Wehrenberg]

Peter,

That is the nice thing about our coaches. Each of us gets to use them as we choose.

This is strictly my opinion and thinking on the topic, but I fall into the "keep the batteries charged up" category. I think nothing of shutting of the generator at night and not turning it on in the morning if we are going to drive if the batteries are still 12.2 or above. We can make coffee, watch TV or do almost anything we need to do and we are still OK.

But from the battery charts that I have seen (and haven't been able to find quickly) once the batteries do get below my preferred charging point their power falls off quickly. So for me it is no big deal to start the generator.

Everything mechanical has limits, and as we use our stuff at the limits I suspect it adversely affects the product life, whether it is a battery voltage or an airplane engine CHT.

I think your analysis is absolutely correct and folks that are dry camping can get more time between charging cycles by following what you said. But a deep discharge has its price in the number of charge cycles. Someday I will try to figure out if batteries actually last longer by only allowing moderate discharges, compared to deep discharges. I believe that if the number of cycles of deep discharge is 1000, but the batteries get 5000 by never letting them go below 12.2 for example, you will need many more charge cycles, but do you need 5 times as many?

BTW, I like running my generator and loading it up. I spent a lot of money to get a coach that has one, I spend a lot of money to drag that dead weight along on trips, so my attitude is to run it until it wears out, which is not likely to happen any time soon.

[jack14r]

Jon,The Lifeline battery, MK battery, and the Deka battery web sites all have charts on percentage discharge that agree with what you are saying.MK and Deka charts agree that the Gel is better than the AGM for deep discharge use.A battery that is 75% discharged has a much shorter cycle life than a battery that is only 50% discharged.I rarely let my generator auto start,like you I like them topped off.

[Jeff Bayley]

I thought I had been informed from several sources including POG postings that letting the batteries fall below 12.2 was bad for them. I attributed that to my batteries giving bad peformance so the next time I changed them, I gave special attention to keeping them up. Still, I got cruddy performance. My batteries drop from 12.9 or 12.7 to 12.0 or so within a half hour to an hour. The drop from 12.0 to 11.0 takes a lot longer, actually giving "better" performance in a manner of speaking. But if I go to bed dry camping, it's a toss up if the fridge is still on the morning.

[gmcbuffalo]

Jeff
Have you compared the voltage reading on your meter with a voltometer attached to the battery bank. I have two voltage meters above the dash, one will read 11.9 while the other one reads 12.4. The 12.4 one reads the same as a direct reading off the battery bank with a voltometer.
GregM

[jelmore]

I'm just passing on what I've read. I don't know that I really understand it.

http://www.lifelinebatteries.com/manual.pdf is my reference.

Their literature says "For repetitive cycling, chargers should have a current limit of at least 0.2C (20 amps for a 100 Ah battery). If the charge current limit is less than this value, the cycle life is adversely affected."

These 8D batteries are rated at 255 amp hours. Does that mean the batteries should be bulk charged at 50 amps (2.55*20)? If so, would that indicate 2 chargers at 25 amps each? Makes me think my charger settings are set up wrong with 20 amps on one and 5 amps on the other and power sharing off. Then again, I don't really know how my chargers should be set up with regard to power sharing, dual ac inputs, etc. I do know that I seem to need all the amps I can get inside.

The last page in that pdf file shows that the number of cycles dramatically increases the less the battery is discharged between charging cycles. For example, 50% (12.13 volts) = 1000 cycles and 10% (12.65 volts) = 5000 cycles.

Liberty has their Watchdog set to start the generator at 11.5 volts which is about an 85% discharge which would be about 500 cycles.

If someone would care to, please correct anything that I've got wrong.

[Jon Wehrenberg]

I doubt if there is a universal answer. We all use our coaches in different ways, and even that changes from time to time depending on circumstances.

We previously dry camped when on the seminar or trade show tours in our first bus. We often found ouselves parked next to one of the regional sales offices / warehouse and I would do several days of sales calls and seminars with the sales agents. Weekends were ours so we would go to a campground, dump and fill and stay hooked up or be driving to the next city where I was scheduled to help the sales reps.

We ran the generator as needed. It was easier than screwing around with a coach that had manual switching and wasn't always user friendly.

Today the only time we run the generator is if we are on the road and stop in a rest area. The rest of the time we spend in campgrounds with an occasional rare spell of dry camping. So our charge rate is set at the minimum and it does not recharge the batteries, as much as it maintains the batteries.

By setting it at the minimum, we can be energy pigs on 50 amp shore power without worrying if the chargers in the inverters will kick on and pop the shore power breaker. We can run a couple of AC units per leg, plus the HW heater and make coffee or watch TV. If we dry camped often I would have the inverter charge rate set up to the max allowed.

In about 6 months my batteries hit the five year mark and thus far there is no indication they are ailing or in need of replacement. I am tempted to see how far they go before they do start acting up, although I know once one does start to fail it creates a lot if problems, especially likely on ours because of the programmable logic controllers that run so much of the coach.

[jelmore]

Starting to make some sense. We use our coach the same way as you Jon, though we're in it full time. So I guess the batteries are maintained in the float stage most of the time, when driving and when plugged in. The only time they drop down and they have to bulk charge (cycle?) is when dry camping.

[Yankee802]

Automatic stuff is for sissies.

After all it is a luxury coach right?

Seems kinda like an oxymoron.

(I couldn't resist)

[dmark1]

Ok a newbie question: No one ever explained this to me (threw me the keys) so....

When you stop at night (say at a rest stop) enroute do you run the generator at night when you have the air conditioners on or do you (assuming no shore power) just let the inverters run the whole thing until the generator kicks on (auto position) to charge them? If that is the case doesn't the constant discharging and recharging of the battery banks cause a shortening of life of the batteries? What do most of you do in this case?

Thanks again

Mark