Typical Voltages and Electrical Battery Charging Issues

[Woods]

Plugging into the shore power doesn't really seem to charge the battery? The battery was brand new last year. My question is on charging. The voltages below were measured under different conditions. The one constant was my Maxxair 4 speed vent fan was on high. The only conditions that charged the battery was the motorhome running or an external battery charger connected? The generator and shore power didn't raise the coach battery voltage above 12 volts? Only a large battery charger or the coach running seem to charge the battery? I can never get through a night on battery power? The battery lasts a few hours then dies. All lights off and refrigerator on automatic the coach is dead before morning?

 

[calvin99]

I'd recommend getting a good battery monitor to see actual state of charge and how much current is being supplied/consumed. Personally, I use Victron SmartShunt, but any of their BMV models are very good. SmartShunt is simplest to install and use if you're comfortable using an app and bluetooth to see what's going on. Battery monitors - Victron Energy

Using a battery without a battery monitor is like driving a car without a fuel gauge and just guessing how much fuel you have. Voltage is not a reliable measure of state of charge and provides no indication of how much energy you are using or supplying to the battery

 

[Bob K4TAX]

With a "just battery" of10.89 volts, likely the battery was discharged too far and is now a very heavy door stop. Take it to Auto Zone, Pep Boys, NAPA, or one of the auto parts stores and they can test it for you. And they can also sell you a new battery, which you will likely need.

Also, the 11.57 volts tell me that the converter is not charging the battery. It should be more like 13.6 volts and then taper to 13.1 volts for a float voltage.

The truck running is charging and the external battery charger is charging. This presumes the battery is good. But your description of lasting for a few hours and then being dead is the sign of a bad battery.

Bob

 

[B52Bombardier1]

All good advice above and you don't mention the amp-hour capacity of your battery. You probably don't realize how much power you are consuming (volts x amps = watts or power consumed) with your fan and lighting etc. It is likely a lot for whatever size of battery you have.

I switched every lamp in the trailer to LED's and greatly lowered my power consumption.

Rick

 

[Bob K4TAX]

I agree with LED lights. I switched all of the original incandescent light bulbs to direct plug-in LED's. What did I gain? With all 10 LED's on, they will consume about the same energy as ONE incandescent. Now THAT is energy saving which translates to longer battery usage.

In another area, I added an accumulator tank after the water pump. This reduces the cycling, provided smoother water flow, and reduces pump surging and related DC current demand. Another battery energy-saving measure.

Bob

 

[Woods]

Thank you all for these suggestions! Bob, I am interested in the accumulator tank (do you have model numbers, pictures or advice). I have already switched all bulbs to LED. I will remove the battery and take it for diagnostics and reinstall with a monitor. I really have no idea how much power the refrigerator uses. When in automatic, I think it defaults to battery? When the battery is dead, the propane option won't work. Most of the time the battery will not even start the generator. I have to start the truck to have enough power to start the generator. Thank goodness the coach battery charges from the truck!

 

[calvin99]

The refrigerator needs 12v for the control system in order to use propane. A 2 way refrigerator uses 120vac when connected to shore power and propane when disconnected from shore power. A 3 way refrigerator has the ability to operate on 12vdc, but that should only be used while driving. If the engine isn’t running a refrigerator using 12vdc for cooling will drain the battery in a very short time.

 

[Bob K4TAX]

Thank you all for these suggestions! Bob, I am interested in the accumulator tank (do you have model numbers, pictures or advice). I have already switched all bulbs to LED. I will remove the battery and take it for diagnostics and reinstall with a monitor. I really have no idea how much power the refrigerator uses. When in automatic, I think it defaults to battery? When the battery is dead, the propane option won't work. Most of the time the battery will not even start the generator. I have to start the truck to have enough power to start the generator. Thank goodness the coach battery charges from the truck!

If the refrigerator is an AC or LP unit, it will require 12 volts to operate the control panel and to ignite the LP burner. Normally, one sets it to AUTO mode and makes sure the LP tank is on and has gas. The refrigerator does the rest. If AC is available then it runs on AC. If not then it switches to LP.

If it is DC only then it likely has a compressor that runs off of 12V DC. There may be a control that automatically switches to AC and supplies DC to the refrigerator when available. If AC is not available, then it switches to the battery. Typically they pull 4 to 6 amps. Based on 50% run time, this will pull a 100 aH battery down in ~20 hrs. (~ rough math)

As to the accumulator: Shurflo 182-200 or SEAFLO SFAT-075-125-01. Both are available from Amazon for about $39.00 I don't recall which one I ordered. I seem to think it is the SEAFLO unit. Easy to install in the line on the output side of the pump.

Bob

 

[Woods]

If the refrigerator is an AC or LP unit, it will require 12 volts to operate the control panel and to ignite the LP burner. Normally, one sets it to AUTO mode and makes sure the LP tank is on and has gas. The refrigerator does the rest. If AC is available then it runs on AC. If not then it switches to LP.

If it is DC only then it likely has a compressor that runs off of 12V DC. There may be a control that automatically switches to AC and supplies DC to the refrigerator when available. If AC is not available, then it switches to the battery. Typically they pull 4 to 6 amps. Based on 50% run time, this will pull a 100 aH battery down in ~20 hrs. (~ rough math)

As to the accumulator: Shurflo 182-200 or SEAFLO SFAT-075-125-01. Both are available from Amazon for about $39.00 I don't recall which one I ordered. I seem to think it is the SEAFLO unit. Easy to install in the line on the output side of the pump.

Bob

I confirmed the model number. It has two modes AC or Gas. Good to know.

 

[Bob K4TAX]

I confirmed the model number. It has two modes AC or Gas. Good to know.

If you use the AUTO mode, it will switch to AC when shore power is available. If shore power is not available it will switch to Gas. It does require that 12V DC is available, either from the onboard battery or the tow vehicle to power the control board and ignite the LP. That is a minimal amount of DC current required.

Bob

 

[Woods]

I am waiting on the power monitor. My smart battery charger indicates the battery is fine. When the battery monitor arrives and I disconnect the battery. I'll take it to AutoZone for a check. I think that I may need a new converter/battery charger (11.57 volts). I am not sure the type supplied in a 2001 Coachmen. I haven't been able to find it? Maybe, it's mounted underneath the coach? Anyway the new ones seem to be microprocessor controlled and multi-stage. My RV manual seems to recommend not leaving on shore power too long due to overcharging? The new smart chargers and hopefully converters should manage that automatically. Sounds like a good upgrade. Anyone have an opinion or suggestion on a converter? I am considering the PowerMax PM3-100 100amp. I keep thinking that I am finished upgrading. But, it seems to be an ongoing process

 

[Woods]

Thank you all so much! After 11 months the battery was shot. The place that I always buy batteries has gone out of business. I am camping next week so I just got a 100ah Diehard from Advance Auto. The Victron Smart Shunt is installed and the app is connected. Generator starts right up and lights are bright! The charging voltage from the converter increasing as current into the battery decreases.

 

[Bob K4TAX]

I am waiting on the power monitor. My smart battery charger indicates the battery is fine. When the battery monitor arrives and I disconnect the battery. I'll take it to AutoZone for a check. I think that I may need a new converter/battery charger (11.57 volts). I am not sure the type supplied in a 2001 Coachmen. I haven't been able to find it? Maybe, it's mounted underneath the coach? Anyway the new ones seem to be microprocessor controlled and multi-stage. My RV manual seems to recommend not leaving on shore power too long due to overcharging? The new smart chargers and hopefully converters should manage that automatically. Sounds like a good upgrade. Anyone have an opinion or suggestion on a converter? I am considering the PowerMax PM3-100 100amp. I keep thinking that I am finished upgrading. But, it seems to be an ongoing process

If you have one of the older style converters, one that uses a saturable core reactor, then yes, don't leave it plugged in indefinitely. If you have a converter that is a "smart converter" then it has 3 or 4 stages of charging and will not overcharge a battery.

For an efficient converter, I suggest talking with the folks at Progressive Dynamics. They have a wealth of accurate information and can correctly advise you on the proper choice for your application.

Bob

 

[Woods]

The smart shunt was a good upgrade! Now I can see that the converter is pretty much junk. Seems to always stop charging at 12.6 volts. The truck running charges until 13.7 volts. (see below) When the converter stops the truck will still push over 30 amps into the battery. Dry camping is pretty much impossible with the generator . Must use the truck engine. 1st picture truck. 2nd picture generator. Tested back to back.

As noted above, I will need to upgrade my converter. Or possibly just plug in my 100amp microprocessor controlled charger with the generator running? Or just continue to run the truck (V10 engine) to charge the batteries. For 3 day weekend mileage went down from 7mpg to 5mpg for battery charging gas use. Is it safe to use a battery charger while using the motorhome and appliances? What do you all think about upgrading to a combination converter / inverter (multi-stage, microprocessor controlled)? Appliances and charging work fine when truck is running and voltage gets close to 14v. Thanks for all your help!

 

[TheLooks]

First let me go back to the fridge issue. No matter what source of power it is using you need 12v dc. If you are on shore power or generator, or propane, 12 vdc still runs the show. It is the control power regardless of what is doing the hard work. It is safe to use a charger to maintain the batteries. Most if not all maintainers are low amperage and are not made to supply fast amps. You only have one battery and when it is taxed the convertor fills in the gap. Speaking of one battery, you will need more then one to run an inverter for long, a 100 ah battery is only good for half that or you will damage it. I recommend doing a lot of research on this subject to get better acquainted with how batteries and the related equipment work. It is not rocket science but I don't think it is intuitive for many. Take the time to learn Ohms law. Watts = Amps x Volts. Amps = Watts/Volts. Volts = Watts/Amps. Just understanding this and the reality of how much power(watts) is available from a given battery will serve you well. And this...https://deepcyclebatterystore.com/how-to-maintain-batteries/

 

[TheLooks]

You mentioned buying a 100 ah battery.....I hope it was a marine/rv battery or deep cycle type.

 

[Kevin D Pem]

Wow!
Long post to have missed so much.
A lead battery dead voltage is 12.0 anything less tells me a cell has shorted or fallen out of the circuit.

What is the converter voltage with the battery out of the circuit?

12.67 = full charge of a sitting disconnect battery! The converter voltage should be 13.6 minimum to fully charge the battery!

It is a slow charge at best at 13.6 so we are talking days not hours.

As I recall MD on a marine battery means deep cycle. You should make sure the battery is not a starting battery.

A rv fridge likely will not run with battery voltage of 12v.

The only way to make it thru the night on battery power is to start with a fully charged battery. Even then a furnace running the chance of making it thru with 100ah is a crapshoot.

 

[Woods]

A good point about the furnace fan. We slept with the door open (just screen). The heat was set to 68 and never came on. Heating requirement would be a whole new variable.

The Diehard is 100ah AGM battery. Running the truck for an hour or so in the morning and an hour or so before bed worked great. Using the Victron shunt, I would make sure nonessentials were off before leaving the camper (or going to bed). The Victron would usually say between 16 hours and 4 days left depending on the current load. With only sensors and refrigerator on, I would usually draw between 0.8 to 2 amps. Usually the batteries were about 80% in the morning and 80% upon returning for bed. I would charge the battery every morning and night until indicator said 100% and amps went below 2 amps. Extra battery capacity would be great. I don't camp without power very often and extra battery would take up cargo storage. So weighing the pros and cons. Thanks for all you guys help. The Victron gives a lot of visibility into the battery usage and charging. Using the converter / generator to charge did very little to actually charge the batteries. They would trickle charge until 12.6 volts and then stop per the pictures. I haven't checked the voltage with the batteries disconnected yet. I have a MagneTek 900 Series Converter. The Victron helped make this an awesome first trip of the year! I'll have maybe 2 more trips without shore power.

 

[Woods]

I plan to install the plumbing accumulator tank next month. The battery monitor and accumulator tank should be standard equipment. Dry camping is nothing but guess work without the monitor. Thanks again for all of your help! Looking back on all my adventures, I wish that I had never bought a new generator (mine went out). Only need enough power to run the microwave for 3 minutes each day. $5000 for a bag of microwave popcorn is too much! Maybe the generator would be useful, if the converter actually had the power to charge my batteries in a short amount of time (like the truck). I can't stand to hear the generator run continuously for days to slowly trickle a battery charge. I might spend even more on this money pit and get a real converter / charger? Probably just make do!

 

[Bob K4TAX]

I plan to install the plumbing accumulator tank next month. The battery monitor and accumulator tank should be standard equipment. Dry camping is nothing but guess work without the monitor. Thanks again for all of your help! Looking back on all my adventures, I wish that I had never bought a new generator (mine went out). Only need enough power to run the microwave for 3 minutes each day. $5000 for a bag of microwave popcorn is too much! Maybe the generator would be useful, if the converter actually had the power to charge my batteries in a short amount of time (like the truck). I can't stand to hear the generator run continuously for days to slowly trickle a battery charge. I might spend even more on this money pit and get a real converter / charger? Probably just make do!

A $650 Champion generator, 2500 watt inverter, will do the job and save you $4300. If your converter won't charge the batteries, I'd say one needs to look at the type and size of the converter. Ours is a 50A-rated converter and will bring our batteries to full charge in less than 4 hrs., depending on the level of discharge.

Bob