Measure coach battery capacity

Topic: Measure coach battery capacity - by Wyatt (Read 1473 times) previous topic - next topic

Measure coach battery capacity - by Wyatt

May 17, 2013, 05:30:55 pm

The "who makes Prevost" thread includes blogs about batteries, so here is some information on determining how good your batteries really are.

I have a ten year old Gel 8D which started at 220AH and still measures 170AH in a ten hour test.

I also have two AGM 8D (Concourd Lifeline) which the manufacturer claims have 255AH, but I have never tested them.

When the Gel reaches 140AH, or suddenly dies which old batteries will do, I will replace it.

How to measure:
Disconnect a fully charged battery and measure the voltage with a digital voltmeter. Let the battery sit disconnected for twelve hours, then measure the start voltage . Attach two head light bulbs (total 10 amps) to an 8D battery and measure voltage & current every hour for ten hours. Measuring the voltage & current every 10 minutes for the first two hours will demonstrate little understood characterists of batteries. If you are curious, plot these numbers on graph paper and you will notice that the voltage drop is not linear for the first hour, but does become linear after the first hour and stays that way until the battery is almost discharged. After ten hours of head lights (close to 100AH used), disconnect lights and measure the voltage. Now let the battery sit disconnected for 12 hours, then measure the final voltage with the same digital voltmeter you started with. Now compare start voltage with the final voltage and note the voltage drop which occurred. Compare these voltages to the charge level chart below to determine the % of battery capacity used according to the charts. Multiply the amps measure (should be fairly constant over the ten hours) and mutiply by minutes or hours to determine how many amphours your battery provided during the test. Now compare the amphours consumed to the % of discharge to determine the actual number of amphours available from your battery.

State of Charge   12 Volt battery
100%   12.75
90%   12.50
80%   12.42
70%   12.32
60%   12.20
50%   12.06
40%   11.90
30%   11.75
20%   11.58
10%   11.31
0   10.5

You can make your batteries last longer by using desulfators. I have one on each battery, purchased from Wizbangplus.com on eBay.

I have available a detailed description of RV battery use and plan to look at what Barry has available and perhaps sent these details for inclusion on his web site.

Re: Measure coach battery capacity - by Wyatt

Reply #1 – May 17, 2013, 06:02:44 pm

Quote from: P. Wyatt Sabourin – May 17, 2013, 05:30:55 pm

You can make your batteries last longer by using desulfators. I have one on each battery, purchased from Wizbangplus.com on eBay.

Wyatt; I use desulfators (BatteryMinder Plus) on all of my "parked" chassis/vehicle batteries (6 Optima red-tops - three in the coach) but have not used a desulfator on the house batteries. Do you disconnect (segregate) your house batteries to use the desulfators, or....... ?

Re: Measure coach battery capacity - by Wyatt

Reply #2 – May 17, 2013, 07:05:23 pm

I am far from an expert but in talking to one today a sealed battery if I understood what he said cannot be "equalized" At 15-16 volts to desulfate the plates.

He uses MK gels as they can be 50% discharged and desulfated

He liked the lifelines as long as they were always at the top of their charge. 2000 cycles. If more heavily discharged he said the cycle life was a small fraction of the gels. 300 versus 1500 was his example on the phone to me today.

Re: Measure coach battery capacity - by Wyatt

Reply #3 – May 17, 2013, 07:50:44 pm

Wyatt, thanks. This is a keeper. I've tried to measure some 8Ds in the past by using the microwave for a given amount of time a given number of times per hour. Pretty primitive but it gave me a general idea. I like your method a lot better!
jor

Re: Measure coach battery capacity - by Wyatt

Reply #4 – May 17, 2013, 09:08:39 pm

Chad, I have the same desulphators and you just connect each one to a battery. They work seperately and do work. In other words take one and put its connections on the pos and neg of a battery then take another and do the same for next battery etc
John h

Re: Measure coach battery capacity - by Wyatt

Reply #5 – May 17, 2013, 10:20:17 pm

Wyatt,

Before you use a "desulphator", go online and check with the manufacturer if they recommend the procedure. With some, it works well, other are dead against it. Most of the modern chargers have either a switch or software to enable/disable it. While you are at it, check the recommended "float" voltage. It also differs from brand to brand and type to type. Again, most modern chargers are able to adjust a custom user selected float voltage

Pierce

Re: Measure coach battery capacity - by Wyatt

Reply #6 – May 18, 2013, 12:03:23 am

Pierce, Wyatt is way ahead of the curve on electrical issues and personally feel he can tell the battery people a few things. His suggestions are well thought out and tested. I listen and read what he puts out and try to follow. IMHO. I have been using them for almost 2 yrs on my AGMs even though the charging is custom set up to cover all basics and more,( and a big thing is I use solar for charge) with Lifelines assistance.
John

Re: Measure coach battery capacity - by Wyatt

Reply #7 – May 18, 2013, 01:22:02 am

John,

Was not aimed at Wyatt but others members that may change to another battery type but not be aware of the differences in both float voltages as well as the timed anti sulfation voltage chargers may apply.

How many 6V-92TA DD were damaged by owners feeding them 20-50 multi grade oil instead of a Delo 100 single grade type oil until this and other forums made the point time after time.

Again, others who may not be electrical whizzes were the intended audience, not Wyatt.

Pierce

Re: Measure coach battery capacity - by Wyatt

Reply #8 – May 18, 2013, 12:05:53 pm

You can also measure usable house battery capacity if you have a battery meter such as a Trimetric or Linklite which use a shunt to measure exactly how many amps are passing in or out of the bank. I check mine by dry camping (no charging from any source) for a night starting with full (float) batteries and read the total number of amps that had been withdrawn by the next morning; that will let you compute what % of the battery's theoretical capacity has been used. Take a resting voltage measurement and calculate the state of charge using the chart mentioned above. The difference will be actual versus theoretical capacity.

Re: Measure coach battery capacity - by Wyatt

Reply #9 – May 18, 2013, 02:31:10 pm

Chad:
The desulfators I use are passive and do not charge the battery.
They draw amps (circa 60 milliamps ie .06 amps) from the battery and 1000 times/second supply a 50 volt 6amp spike to the battery.

The desulfator is connected to the positive and negative posts of the battery with short leads - connected any where else it will not work. It is connected to the battery without disconnecting any of the other wires. The desulfator will not effect the workings of your 12 volt system. This may appear to be like magic, however, if you dismantled your laptop computer and looked at the WIFI antenna, you would wonder how it works because the outer end is grounded.

In my opinion, using a desulfator on a start batteries does not provide as much benefit as using a desulfator on coach batteries. It has to do with depth of discharge.

Caflashbob:
Equalizing can desulfate a battery in a few hours, while desulfating will desulfate a battery in a few months (yes, months). Equalizing causes rapid production of gases, desulfating does not.

Manufacturers of sealed (Gel or AGM) all caution against Equalizing sealed batteries. Equalizing is a controlled fast overcharge which causes the battery to get hot and produce lots of gas. Heat is bad for batteries. Controlling equalizing involves checking the temperature and with sealed batteries watching for over pressure (bulging sides). The battery will not explode because there are pressure relief valves, however if gases are released, the battery looses capacity forever. Solar Mike, from the Slabs told me that he has restored functioning of very old sealed batteries by equalizing, but he will only do it on old batteries because he has also destroyed batteries by equalizing.

MK claims that their batteries are better than others, however, Concorde Lifeline makes the same claim. Concorde claims their Lifeline AGM batteries will cycle as many times as a Gel without the hassle of Gel batteries. Based on my experience, I do not believe it. I have Lifeline AGM batteries which are constantly outperformed by my ten year old Gel.

Any real deep cycle battery can be discharged below 50%, and even as low as 20%. The number of times a battery will cycle in it's lifetime is reduced with increasing depth of discharge.

You make an interesting observation. Cycle an AGM below 50% on each cycle and it will provide only 300 lifetime cycles, while a Gel would provide 1500 cycles. I am not sure about this.

Pierce:
There is some contraversy regarding the benefit of using desulfators. An independant laboratory published this "while desulfators seemed to increase the charged voltage of batteries they do not appear to increasing the number of amphours available".

As far as checking manufacturers recommendations regarding use of desulfators, it is way to late for me because I have been using them for years. I bought components and built my own about 2005.

My own experiments have lead me to believe that desulfators are beneficial and I will continue to use them. My ten year old Gel has cycles at least 1600 times and still functions well.

You mention "float voltage", but I believe that needs to be a new thread because there is contraversy and many different opinions about what is correct. Trojan and Interstate have, for instance, both published papers indicating that the settings we have been using when charging ( ie voltage for bulk, absorption, float) leave batteries undercharged. They are now indicating that the initial float voltage should be higher then previously stated. I am in the process of experimenting with this and am not comfortable commenting yet.

John: Thanks for the vote of confidence.

2Escapees:
I do what you mentioned and have amphour meters with a shunt for each battery (thanks to Barry Leavitt for this idea).
Adding Shunts to Batteries
The awkward part is letting a battery rest to obtain a valid voltage while dry camping.

Re: Measure coach battery capacity - by Wyatt

Reply #10 – May 18, 2013, 06:07:06 pm

Quote from: P. Wyatt Sabourin – May 18, 2013, 02:31:10 pm

Chad:
The desulfators I use are passive and do not charge the battery.
They draw amps (circa 60 milliamps ie .06 amps) from the battery and 1000 times/second supply a 50 volt 6amp spike to the battery.

The desulfator is connected to the positive and negative posts of the battery with short leads - connected any where else it will not work. It is connected to the battery without disconnecting any of the other wires. The desulfator will not effect the workings of your 12 volt system. This may appear to be like magic, however, if you dismantled your laptop computer and looked at the WIFI antenna, you would wonder how it works because the outer end is grounded.

In my opinion, using a desulfator on a start batteries does not provide as much benefit as using a desulfator on coach batteries. It has to do with depth of discharge.

Caflashbob:
Equalizing can desulfate a battery in a few hours, while desulfating will desulfate a battery in a few months (yes, months). Equalizing causes rapid production of gases, desulfating does not.

How do I get desulfators? Buying new gels.

Re: Measure coach battery capacity - by Wyatt

Reply #11 – May 18, 2013, 06:23:24 pm

Bob,

These are standard on an new Newell. Best price when I got mine was Aircraft Spruce.

http://www.pulsetech.net/XC100P-Xtreme-Charge-12V-Battery-Maintenance-Charger-Desulfator-7346.aspx

Re: Measure coach battery capacity - by Wyatt

Reply #12 – May 18, 2013, 07:11:42 pm

Go to Amazon in auto and type in Wizbang and a bunch will come up. They are $25 each and you do not need a charger for this .
John h

Re: Measure coach battery capacity - by Wyatt

Reply #13 – May 18, 2013, 08:10:09 pm

They're no doubt a good thing. But it looks to me I'd have to remove at least 2 of my 3 AGMs to attach the Wizbang.

But Amazon charges shipping. Even if you have Prime.

best, paul

Quote

Go to Amazon in auto and type in Wizbang and a bunch will come up. They are $25 each

Re: Measure coach battery capacity - by Wyatt

Reply #14 – May 18, 2013, 08:51:17 pm

John,

Seeing your post, I revisited my link to Pulsetech and found they do not offer just a desulfator anymore. My Pulsetech desulfator is just like to ones in your link and would be my choice if buying today too.

I have a battery maintainer to float my chassis batteries anytime I am plugged into shore power or the gen is running.

I just put the positive lead to the positive post and the negative lead to the negative post with out disturbing the connection to the batteries. Took 5 minutes per unit.

Re: Measure coach battery capacity - by Wyatt

Reply #15 – May 19, 2013, 12:02:35 am

Paul, can you not just get to the bolts to take nuts off clamps?? That's all you need to do.
John h

Re: Measure coach battery capacity - by Wyatt

Reply #16 – May 19, 2013, 12:07:41 am

Possibly. With 1 of the 3.

best, paul

Quote

Paul, can you not just get to the bolts to take nuts off clamps?? That's all you need to do.

Re: Measure coach battery capacity - by Wyatt

Reply #17 – May 19, 2013, 12:52:36 pm

Quote from: Caflashbob – May 18, 2013, 06:07:06 pm

How do I get desulfators? Buying new gels.

I bought four from "wizbangplus.com" on eBay for $20 and they seem to be working. I will scope them later in the summer and compare to the originals which I bult in 2005.

Wyatt

Re: Measure coach battery capacity - by Wyatt

Reply #18 – May 19, 2013, 06:48:51 pm

Hi Wyatt,

I'm curious what frequency you designed in your home-built desulfator. Is there some logic to an exact frequency and voltage? How will you actually know the $20 units perform as well as the high dollar offerings?

Jim

2002 U320

Re: Measure coach battery capacity - by Wyatt

Reply #19 – May 20, 2013, 09:01:45 am

Quote from: P. Wyatt Sabourin – May 17, 2013, 05:30:55 pm

... Multiply the amps measure (should be fairly constant over the ten hours) and mutiply by minutes or hours to determine how many amphours your battery provided during the test. Now compare the amphours consumed to the % of discharge to determine the actual number of amphours available from your battery.

Wyatt - I'm one of those "less experienced" would you possibly give an example of the two calculations you're talking about in the above quoted portion of Battery Capacity calculations? Thanx!

Re: Measure coach battery capacity - by Wyatt

Reply #20 – May 20, 2013, 04:32:02 pm

Jim, very good questions:

I did not design the desulfator circuit.
The frequency was set to 1Khz by an 8 pin LM555IC chip.

I purchased desulfator kits in July 2003 from Don Denhardt who perfected the design work which was publish by a group called "Home Power".

The "Home Power" group was composed of people using solar power to be "off the grid". Extending battery life cycles/years was very important to them due to the high cost of replacing a home power battery bank. Experimenting was done in the 1990s and an article on "24 volt desulfator circuit" was published in the june/july 2000 issue of the "Home Power" publication.

The logic just involved safety, cost, and longevity. Yes, increasing the voltage, frequency, and duration of the spikes will more rapidly desulfate a battery, however at what cost, risk and for what reason? A battery or things connected to that battery can be permanently damaged by rapid desulfating or equalizing and some batteries were damaged during testing. The intent here is to install a device to each battery which will extend the life of the battery without endangering people with electric shock or damaging 12 volt devices at a justifiable cost.

Here is a 200 volt desulfator built for a large battery bank.
http://www.aeroelectric.com/Reference_Docs/Battery/Desulfator/High%20Power%20Desulfator.pdf

I will know my $20 desulfator is working when the fully charged voltage of my AGM batteries has been increased from 12.8 volts to 12.9 volts, or perhaps 13.0v. I am not sure I will ever know if my low cost desulfators perform as well as a high dollar one.

The fully charged voltage of my Gel battery is 13.0 volts and is about 0.2v higher than the AGM battery voltages.

This voltage difference between the Gel and the AGM batteries has occurred because the Gel has been desulfated almost continuously for nine years while the AGM batteries were being desulfated only half the time because I only had two desulfators. I discovered that the desulfator being used on the AGM batteries had stopped working. I purchased four wizbangplus desulfators so now both AGM batteries are being desulfated continuously and have been for almost a month. I should see increasing voltages on the AGM batteries for the next 4 months.

Right after sunset, when the solar controller reads zero amps, the voltage difference between the Gel and the AGM batteries causes the amphour shunt on the Gel battery to read -1.5a, and the amphour shunts on the two AGM batteries to read +0.5a and +0.7a. The 1.5 amps from the Gel battery is going to the two AGM batteries (1.2a) and the phantom load (0.3a). This draw from the Gel battery to the AGM batteries lasts about an hour. As the AGM batteries become desulfated, this Gel charging AGM should stop.

When running the microwave from the inverter, the amps to the inverter comes from all three batteries but not equally. One AGM battery provides 20%, and one AGM battery provides 25%, while the Gel battery provides 55%. This occurrs even though the Gel battery is just behind the driver seat and has 000 wires which are 30 feet long on both negative and positive wires. The inverter is under the foot of the bed, very close to the AGM batteries which are behind the rear passenger duals. I am guessing that the AGM batteries will each provide more amps to the inverter as they become desulfated (due to higher voltage and lower internal resistance).

Re: Measure coach battery capacity - by Wyatt

Reply #21 – May 20, 2013, 05:04:44 pm

The amphour calculation can be done as follows:

At the beginning of the ten hour test, the two headlight high beams will draw about 9.6 amps.
The amps at the end of the ten hour test with these two headlight high beams will be about 8.8 amps because the voltage will drop during the test. The average of 9.6 and 8.8 is calculated by adding 9.6 + 8.8 = 18.4, then dividing by 2 = 9.2amp. Multiple amps (9.2) by hours (10) to get 92 amp hours. A good 8D battery with 240 amphours capacity will have been discharged by 92/240 = .38 ie 38% and should still have available 100-38 = 62%. A battery with 62% of its amphours left will have a voltage of about 12.30 volts. If the voltage is lower, ie 12.12 volts which, from the "voltage/percent charged" table means the battery has only 40% of its amphours left and the ten hour test has used 100-40 = 60% of its amphour capacity. The battery's amphour capacity is 92 times 100 divided by 60 = 153 amphours. The battery has only 153/240 times 100 = 63.75% of its original capacity. The question then would be "are you willing to carry around a 165 pound battery for 153 amphours".

Re: Measure coach battery capacity - by Wyatt

Reply #22 – May 21, 2013, 10:13:11 am

Quote from: P. Wyatt Sabourin – May 20, 2013, 05:04:44 pm

The amphour calculation can be done as follows:

Thanks Wyatt...

Re: Measure coach battery capacity - by Wyatt

Reply #23 – May 21, 2013, 04:46:14 pm

Quote from: P. Wyatt Sabourin – May 20, 2013, 04:32:02 pm

When running the microwave from the inverter, the amps to the inverter comes from all three batteries but not equally. One AGM battery provides 20%, and one AGM battery provides 25%, while the Gel battery provides 55%.

this is hopefully now even on mine after connecting the 3 agm s to a common buss bar and taking the feed from that. As he said it may be a while before you find out if all is well but it is better than the usual hook up (I believe).
There must be something wrong with me as here we are just arrived in the hotel at Dusseldorf Airport and I am checking the Foreforums website!! it is 10 45 pm and we have to be up at 4 am for a plane at 6 am??? Nuts after along trip from vancouver BC!!
John H

Re: Measure coach battery capacity - by Wyatt

Reply #24 – May 21, 2013, 08:54:18 pm

We just got back from two weeks in England. Had to get up at 4:00am to get to Heathrow, turn in the rental car, catch a plane to Lisbon to connect to one to Newark. So I've been up since 11:00pm last night Newark time, and what am I doing? Checking the forum of course!

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