BATTERY LIFE

Anything electric, AC or DC

BATTERY LIFE

Postby bc toys » Fri Feb 23, 2018 9:01 am

I was reading something here while back that you don't want your battery to get below 50% well can anyone tell me what the voltage will read at 50%
I read where a guy let his voltage go down to 11.4 volts that seems low to me unless he is getting below 50% I've never had mine get below 75% yet sense
I got the solar system
bc toys
2000 Club
2000 Club
 
Posts: 2217
Images: 42
Joined: Sun Jun 28, 2009 2:45 pm
Location: LAS VEGAS NV

Re: BATTERY LIFE

Postby lfhoward » Fri Feb 23, 2018 9:12 am

This battery webpage has almost everything you need to know about RV (and ttt) electrical systems, including a power chart. They say 12.06 is 50% charge.

http://rvroadtrip.us/library/12v_system.php

Of course that wouldn’t be 12.06 volts under load, but after the batteries have had a chance to equalize.
My off-road camper build on an M116A3 military chassis:
http://www.tnttt.com/viewtopic.php?f=50&t=62581
Tow vehicle: 2008 Jeep Liberty with a 4 inch lift.
User avatar
lfhoward
The 300 Club
 
Posts: 463
Joined: Wed Jan 22, 2014 6:10 pm
Location: Philadelphia, PA

Re: BATTERY LIFE

Postby friz » Fri Feb 23, 2018 12:55 pm

Same for me. I have an AGM battery and my cut off is 12v.

Sent from my SM-G930V using Tapatalk
The "Sin Bin"
150133
User avatar
friz
The 300 Club
 
Posts: 396
Images: 2
Joined: Mon Jan 03, 2011 10:01 pm
Top

Re: BATTERY LIFE

Postby John61CT » Fri Feb 23, 2018 1:25 pm

Totally varies with the chemistry type, specific model, resting time isolated before measuring, and then changes over time as the capacity declines as the bank ages.

Bottom line is, voltage is a very inaccurate guestimate of State of Charge.

Even the best (expensive) battery monitors can easily be off by 8+%

Best combination IMO if you can justify the investment is a Merlin/Balmar SmartGauge + Victron 702-BMV.

Otherwise just the SG.

Search http://marinehowto.com for "battery monitor".
John61CT
500 Club
 
Posts: 791
Joined: Thu Nov 17, 2016 4:36 pm
Top

Re: BATTERY LIFE

Postby Socal Tom » Fri Feb 23, 2018 1:57 pm

I try to keep mine above 12.2. John is correct, voltage isn't a very accurate measure, but just about every one of the charts I've found says 12.2 should be ok. However, I don't actually start to panic until it gets below 12.
Tom
Socal Tom
Donating Member
 
Posts: 1056
Images: 9
Joined: Sun Jun 29, 2008 9:21 am
Location: San Diego Ca
Top

Re: BATTERY LIFE

Postby GuitarPhotog » Fri Feb 23, 2018 3:52 pm

John61CT wrote:Totally varies with the chemistry type, specific model, resting time isolated before measuring, and then changes over time as the capacity declines as the bank ages.

Bottom line is, voltage is a very inaccurate guestimate of State of Charge.

Even the best (expensive) battery monitors can easily be off by 8+%

Best combination IMO if you can justify the investment is a Merlin/Balmar SmartGauge + Victron 702-BMV.

Otherwise just the SG.

Search http://marinehowto.com for "battery monitor".


Kinda tough to measure Specific Gravity on a sealed AGM battery, isn't it?
GuitarPhotog
Silver Donating Member
 
Posts: 1700
Images: 55
Joined: Tue Feb 08, 2011 12:52 pm
Location: Grants Pass Oregon
Top

Re: BATTERY LIFE

Postby Aguyfromohio » Sat Feb 24, 2018 10:22 am

Many years ago I was part of an engineering team for the main battery on the F-16.
We could only accurately know the state of charge of the battery by having a little micro processor measure the current entering and leaving the battery, and keeping a running tally of amp-hours remaining. We had a PhD electrochemist on the team, he assured us there is nothing you can measure at the battery terminals that tells you much. The more expensive battery monitors like those mentioned above measure current and perform that kind of amp-hour accounting. Our system had a lot of fancy correction factors for temperature, and rate-of-discharge, and cycle life history to improve accuracy.

Of course it may be worth asking the question “why try at all?”
If you are off grid and not able to charge, just use as little power as possible and when the battery is depleted that’s that. If you have a high quality smart charger wired in to the shore power circuit, plug in whenever you can and the battery will stay as charged as possible.

The Air Force cared because they had jet fighters not ready to go due to dead batteries that were being depleted by ground crews and failing early due to abuse. Our system disconnected the main battery at certain points when the ground crews ran the batteriy down by talking sports on the giant military radio or were goofing around too much raising the canopy up and down. They had to go outside to push a RESET button, and our memory data would tell their superior officers who was ruining the batteries and reducing the unit readiness. The average camping trip is less critical.
Aguyfromohio
Silver Donating Member
 
Posts: 170
Images: 44
Joined: Sun Jan 29, 2017 5:02 am
Top

Re: BATTERY LIFE

Postby Socal Tom » Sat Feb 24, 2018 10:29 am

Aguyfromohio wrote:Many years ago I was part of an engineering team for the main battery on the F-16.
We could only accurately know the state of charge of the battery by having a little micro processor measure the current entering and leaving the battery, and keeping a running tally of amp-hours remaining. We had a PhD electrochemist on the team, he assured us there is nothing you can measure at the battery terminals that tells you much. The more expensive battery monitors like those mentioned above measure current and perform that kind of amp-hour accounting. Our system had a lot of fancy correction factors for temperature, and rate-of-discharge, and cycle life history to improve accuracy.

Of course it may be worth asking the question “why try at all?”
If you are off grid and not able to charge, just use as little power as possible and when the battery is depleted that’s that. If you have a high quality smart charger wired in to the shore power circuit, plug in whenever you can and the battery will stay as charged as possible.

The Air Force cared because they had jet fighters not ready to go due to dead batteries that were being depleted by ground crews and failing early due to abuse. Our system disconnected the main battery at certain points when the ground crews ran the batteriy down by talking sports on the giant military radio or were goofing around too much raising the canopy up and down. They had to go outside to push a RESET button, and our memory data would tell their superior officers who was ruining the batteries and reducing the unit readiness. The average camping trip is less critical.

This is a less fancy, less expensive version I use
bayite DC 6.5-100V 0-100A LCD Display Digital Current Voltage Power Energy Meter Multimeter Ammeter Voltmeter with 100A Current Shunt https://www.amazon.com/dp/B013PKYILS/re ... KAb6P71JNN
I have it on a dpdt switch. When discharging it records watt hours used. Then when charging, I flip the switch, reset the guage and it tracks watt hours sent to the battery. It’s not perfect, but easy to see when I’m drawing more than I can afford.
Socal Tom
Donating Member
 
Posts: 1056
Images: 9
Joined: Sun Jun 29, 2008 9:21 am
Location: San Diego Ca
Top

Re: BATTERY LIFE

Postby John61CT » Sat Feb 24, 2018 12:34 pm

GuitarPhotog wrote:Best combination IMO if you can justify the investment is a Merlin/Balmar SmartGauge + Victron 702-BMV.

Otherwise just the SG.

Search http://marinehowto.com for "battery monitor".


Kinda tough to measure Specific Gravity on a sealed AGM battery, isn't it?[/quote]I never mentioned specific gravity, but yes that needs a rest period and per-model calibration for accuracy as well.

In this case I was talking about SG as in the SmartGauge SoC meter.
John61CT
500 Club
 
Posts: 791
Joined: Thu Nov 17, 2016 4:36 pm
Top

Re: BATTERY LIFE

Postby John61CT » Sat Feb 24, 2018 12:39 pm

Aguyfromohio wrote: there is nothing you can measure at the battery terminals that tells you much.
The SmartGauge does not count AH, the rest do, work off a shunt.

The SG is the most accurate of the bunch, gets more and more so as it gets familiar with the bank's use patterns. But the algorithms it uses are proprietary, have not yet been reverse engineered.
John61CT
500 Club
 
Posts: 791
Joined: Thu Nov 17, 2016 4:36 pm
Top

Re: BATTERY LIFE

Postby John61CT » Sat Feb 24, 2018 12:44 pm

Socal Tom wrote:This is a less fancy, less expensive version I use
bayite DC 6.5-100V 0-100A LCD Display Digital Current Voltage Power Energy Meter Multimeter Ammeter Voltmeter with 100A Current Shunt https://www.amazon.com/dp/B013PKYILS/re ... KAb6P71JNN
I have it on a dpdt switch. When discharging it records watt hours used. Then when charging, I flip the switch, reset the guage and it tracks watt hours sent to the battery. It’s not perfect, but easy to see when I’m drawing more than I can afford.
Certainly better than just using voltage.

AH counters get a bit more accurate for SoC readings when they require programming with chemistry type, coulombic charge efficiency, Peukert factor, and current residual AH capacity.

But they get less efficient over time, need regular "now Full" resetting and of course updating the AH capacity as that declines.

SmartGauge requires none of that and is also more consistently accurate.Only works with lead chemistries though, no good for LFP.
John61CT
500 Club
 
Posts: 791
Joined: Thu Nov 17, 2016 4:36 pm
Top

Re: BATTERY LIFE

Postby KennethW » Sun Feb 25, 2018 3:39 am

bc toys wrote:I was reading something here while back that you don't want your battery to get below 50% well can anyone tell me what the voltage will read at 50%
I read where a guy let his voltage go down to 11.4 volts that seems low to me unless he is getting below 50% I've never had mine get below 75% yet sense
I got the solar system
Back to reality. The cost of a battery version camping fun. Yes taking the battery to low is bad but so is cutting the fun short be cause a battery is at 50%. Your call. I call fun and will buy replacement a little early.

Sent from my Moto G (4) using Tapatalk
KennethW
1000 Club
1000 Club
 
Posts: 1038
Images: 82
Joined: Wed Feb 20, 2013 8:01 pm
Top

Re: BATTERY LIFE

Postby tony.latham » Sun Feb 25, 2018 6:33 pm

I use a G.T. Power meter to keep track of both my amp usage and resting voltage. They work great.

For $18 they are a steal. :frightened:

Image

Here's a good analysis of there accuracy:



If I build #4, I'll put one on both sides of the battery to measure power going in from the solar panels and power being consumed.

Tony
Image
User avatar
tony.latham
Gold Donating Member
 
Posts: 2708
Images: 17
Joined: Mon Jul 08, 2013 4:03 pm
Location: Middle of Idaho on the edge of nowhere
Top

Re: BATTERY LIFE

Postby mustangcats » Sun Mar 04, 2018 8:01 pm

tony.latham wrote:I use a G.T. Power meter to keep track of both my amp usage and resting voltage. They work great.

For $18 they are a steal. :frightened:

Image

Here's a good analysis of there accuracy:



If I build #4, I'll put one on both sides of the battery to measure power going in from the solar panels and power being consumed.

Tony



Thanks for posting information about this meter. I just ordered one on ebay for $10.45 postage paid...it's coming all the way from China! It will come in handy for finding out just how many amps the Truck Fridge is drawing. Last summer when I was at Rocky Mtn. NP there were too many cloudy days and my sole 100 watt solar panel couldn't keep up with the demands of the fridge and the battery voltage dropped too low. Had to use the generator as a backup. The Truck Fridge was advertised as "sips the battery power", but I have found that is not the case in the real world.
User avatar
mustangcats
Silver Donating Member
 
Posts: 230
Images: 18
Joined: Sun Apr 08, 2012 3:35 pm
Location: Iowa
Top

Re: BATTERY LIFE

Postby John61CT » Mon Mar 05, 2018 7:45 am

> Truck Fridge was advertised as "sips the battery power"

Compared to all the other fridge *types*

Peltier coolers
Mains powered
Absorption

All the Danfoss-style 12V compressor are very efficient,

and afaik the AH / day rates are quite similar to each other's
John61CT
500 Club
 
Posts: 791
Joined: Thu Nov 17, 2016 4:36 pm
Top


Return to Electrical Secrets

Who is online

Users browsing this forum: No registered users and 2 guests