Battery Power Management, House Battery, Chassis Battery, etc

Len did say 1.5W which would be on the order of ~125mA.

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OOPS!

It will take about a week to get test results from my radio.  1.5w seems a little high just for that but we will see.

I recharged the battery, let it set 24 hours, measured 12.80v, removed 123 watts from the battery [ 92 watts worth of interior lighting on for 1hr 20minutes] and measured a battery voltate of 12.50v.  I will check the voltage again this evening and if the battery is stablized I will start a 3-4 radio "off" current drain test.  I will pull all 12 volt fuses to EVERYTHING except the radio.

After the radio "off" test I think I will do a radio "on" power drain test with a few hours of Vivaldi "The Four Seasons" at a reasonable inside sound level and get a handle on what the cost is to use the radio while we are w/o shore power.  My radio limit is usually not power used but Joanne.  "Can't we turn that thing off" usually comes just as I am really just starting to get into it.  It wounds me deeply.  As a retired engineer you would think she would want me to widen my horizons beyond flannel shirts and dirty blue jeans?

So I will post again in the this thread in a week or two.

You're assuming that the voltage/SOC curve is linear, which may not be true.  Also, the time to discharge to any given level isn't necessarily a linear function of the load.  And, again, 1.5W is on the order of self discharge of the battery.

Also, the time to discharge to any given level isn't necessarily a linear function of the load.

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You're correct - it isn't. A 10 ohm load at a battery voltage of 12.6 volts would draw 1.26 amps, but when the voltage drops to, let's say 11.5 volts, that same 10 ohm load would only draw 1.15 amps; the change of the state of charge is definitely time dependent.

After recharging and discharging the battery back into the 12.4v range again I have removed all 12v fuses except for the circuit that has the radio on it.  I have watched  the voltage drop for about 64 hours so far.  For what ever reason the radio does appear to be consuming 1.0w to 1.5w per hour in the "off" mode.  Thinks thats high but that is what it is.  We have had some problems w the radio lately.

As far as battery self discharge rate.  The single battery in my RV is a Delco M30HMF marine/RV battery w lead-cad.  I don't think its self discharge rate in rough numbers would be much different than any other lead acid battery of its size.  I do fugure the self discharge rate should be on the order of 0.05watts/hr.  That is less then what Ned is referring to.  As far as I can tell self discharge rate for a lead-acid battery should be on the order of 3% of power per month at least for the first several months of storage.  This would be consistant with my July 28th post were I did not get a measureable voltage drop over a three day period of having the battery disconnected (to 1/100th of a volt).

It is interesting that a day to night temperature swing of 20+ degrees F can be picked up with a voltmeter on the battery.

I still think you're in the range of self discharge.  A 220AH battery has 2640W of power at full charge.  If it self discharges at 3%/month that's 2.64W/day, more than you're seeing.

Ned said:

I still think you're in the range of self discharge.  A 220AH battery has 2640W of power at full charge.  If it self discharges at 3%/month that's 2.64W/day, more than you're seeing.

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Just as I was thinking.  Why not just insure the batteries are fully charged then disconnect the batteries and measure the voltage drop over several days.

Fat fingered the keys and sent message before being done.

Apples and oranges Ned.  We are saying the same thing it turns out.  I am using watts per hour not watts per day.

My Delco M30HMF battery is a 115Ah battery.  So fully charged it would have 1380 watts and 3% per month self discharge would be:  1.40 watts per day OR 0.058 watts per hour.  Same thing after adjusting for units. 

So when I say I am lossing 1.5 watts per hour that is for me a big loss and is about 24 times the battery self discharge rate.

I removed the "fat fingered post" Len. FYI you can edit your posts by clicking the Modify button near the top right of each message (next to the subject line). If you don't see the button, let me know. Thanks.

I get to use that button a lot  :-[

Thanks Tom,

Assuming my search does not turn up any other significant power losses, I think I will rewire the radio power. 

If I remember correctly the radio has two 12v sources of power (a red wire and a yellow wire)r.  Normally one 12v source is the chassis battery directly so that radio memory is not lost when the radio is turned "off".  The second 12v source is through ignition switch.  So if the radio is inadvertently  left on when the ignition is turned off the radio will be turned off to prevent battery drain.  Wanting to be able to use the radio while camped I directly wired both wires to my house battery.  So, while stopped and the engine turned off we can use the radio w/o being concerned about draining the chassis battery.

I think I will pull the my center console (to get at the wiring) and my radio and rewire it.  I will put the 12v memory wire back on the engine battery.  The wire that normally is ignition switched (and I ASSUME at this point is source of my 1.0-1.5w per hour power loss) and that I have hard wired into my house battery I will dual power source it.  I will power the radio with an 12v of chassis power via an ignition switched wire AND power the radio from the house battery through a mechanical timer mounted in the dash.  On the road the radio will play normally off of the engine battery.  Stopped the radio can play for as many hours as I set on the timer off of the house battery.  When the timer times out no house battery drain.  I think this will stop that power drain.

Yep..... right there in plain sight is the "modify" button.  

Len and Jo said:

Yep..... right there in plain sight is the "modify" button.

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The story of my life Len - right in front of my nose all the time. Glad you found it.

I have removed all 12v fuses except for the circuit that has the radio on it.  I have watched  the voltage drop for about 64 hours so far.  For what ever reason the radio does appear to be consuming 1.0w to 1.5w per hour in the "off" mode.  Thinks thats high but that is what it is.

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That wattage equates to about 0.1 amp (100 milliamp) and is in the range of what automotive radios use to keep the memory alive and to sense its electronic switches (i.e so you can turn it on again). It probably also has a digital clock it keeps alive.  They ought to be able to do with less power, but saving on batteries is not a big design issue in automotive electronics - they expect you to drive it every day or at worst 2-3 days.

I think your solution to move the "keep alive" wire back to the chassis battery is a good one.

FYI

I took the direct path and got into the wiring under the dash.  With my multimeter I measured the radio "off" current 95 milliamp and the battery voltage at the time was at 13.1 volts for a power drain of 1.24 watts.  Think I will just add a radio 'kill' switch for multi day boondocking.  Wish I had a similar reading off of the 'old' Delco radio I took out of there 5 years ago to compare to the Jensen radio.

The attached picture is of the modified dash with a 20A toggle switch added below and to the left of the radio.  If we use it, it will save us 30 watts per day of battery power while boondocking.

Follow-up............

External house battery drain is now not measureable (aka: battery voltage) to two decimal places over a 4 day period.  The radio was source of the battery drain.  Now when everthing is off it really IS OFF.   

Think I will start looking at LED lighting options since lights are are largest use.  I'm also going to add a timer in the bathroom for the Fantastic Fan so that it will shut off 1-2 hours after we go to sleep at night.

Thanks for the followup.  Sounds like you have found the battery drains.

Why not use a temperature controller on the Fantastic fan rather than a timer?  Check the web site for a replacement controller.  Ours has a thermostat and it's 10 years old.

For boondocking with finite power I think a timer is best for us.  The thermostat does look like a nice feature though.

Thanks for the idea.

Not sure where you'll find a 12VDC timer readily. If you use a 120ac timer, you'll need the inverter to power it; cuts down on the savings. Yes, 12 volt timers are available, but most are manually operated and don't have a 24-hour clock for day-to-day use.

No power needed.  The timer I am going to use is a mechanical device.  HD has a 1 hour max. and a 12 hour max. versions.  We have one in our home bathroom wired to the shower exhaust fan to remove mosture and not have to think about turning the fan off.  Have also used several in our church kitchen for exhaust fans, point of use water heaters, coffee makers and thermostats (prior to110v  programable thermostats being available).  Do not have to worry about people turning things off because eventually they will shut themselves off anyway. ;D

Well Ned have to thank you again

After looking at the Fantastic Fans available I am going to remove the one I have and install the one with a variable speed fan and re-install my old one behind the front seats (need to measure things a little first).  We have a VERY NOISY 12v fan mounted inside pn a side wall for hot days that I will pitch.  It's an 8" chrome wire cage thing that I got at Camping World and I have never liked it and as a result never really used it.

The two Fantastic Fans will really move the air on warm days and nights.  Being able to set a very low (AND I ASSUME QUITE) speed on the new one when we go to bed will really be nice.  Thanks again my $20 job just had job scope change and large budget increase. ;D  When done I think I will be very happy with the dual fans.

Ah, yes. I guess we did have gears and springs before we had electricity