Voltage Drop in AGM Under Load?

[hellosailor]

Speaking of AGM and the tropics...Wet lead batteries intended for sale and use in the tropics supposedly have a slightly different electrolyte than the ones intended for cooler climates. Are AGMs being sold in the tropics, also built for the tropics? If not, they would suffer "instantly" from capacity loss once they arrived in the tropics.

"I ask this because my variant of Group 31 AGM has 20 more Ah than the standard, yet case sizes are identical, only the XT weighs 10 lbs more."
AGM plates are packed together "solid" with the separators, which should allow them to be packed more densely than wet lead, with a higher weight. Also, there's no need to leave empty space at the bottom of case to allow precipitates to fall out of solution, since there is no free electrolyte. So an AGM case that is "the same" group size, could easily have more plate material and weigh more. Or not--as the maker chooses.

[sailorboy1]

Originally Posted by neelie

Ps..The symptom I had was when drawing 180A using the inverter, the low voltage protection on the fridge compressor shutdown the fridge. if the LED temp indicator on the fridge hadn't turned off, I would never have investigated what I thought was a fridge failure which turned out to be the voltage drop.

It only happened when SOC indicated 80% and did not occur when indicating 100.. (Yes, I know, SOC readings are not accurate.. Only mentioned it to indicate relative capacity).

I still feel that you don't have a problem other than the normal voltage drop during a large load. I know that my 460AH bank at 90% SOC under a 80 amp load (running the Mr Coffee off the inverter) that the voltage at the terminals will drop below 12V. It will go right back to near where it started a few minutes later after the load drops. I have no idea whether my refrigerator shuts down during this but I wouldn't be surprised if it does.

Since this is what your problem is did your electrician measure your voltages under a large load like running the microwave off the inverter?

Maybe you just need a smaller microwave

[neelie]

Sailorboy1. You could be right. I've stopped using the inverter until I resolve the issue.

Mainesail or anyone.. Re Capacity test. Advice needed.

Lifeline documentation recommendation is as follows:

Copy and pasted.....below..



To determine the actual capacity of a Lifeline® AGM battery relative to its rated capacity, a full discharge test should be performed. Although there are various battery testers available on the market, such as carbon pile testers, impedance meters, conductance meters, and others, these testers are not reliable in determining the battery's actual capacity. To determine the battery's actual capacity relative to its rated capacity, use the following procedure:

1. Stabilize the battery at 68-86°F (20-30°C) for at least 24 hours.
2. Bring the battery to full charge as described in Sections 5.4, 5.5 or 5.6 as applicable.
3. Discharge the battery at a constant current of 25 amperes until the voltage falls to 10.5 volts (5.25 volts for a 6 Volt battery). Record the discharge time in minutes.
4. Compare the measured discharge time to the published 25A rating (reserve capacity minutes) for the battery.
5. If the battery delivers less than 80% of the rated capacity the conditioning procedure given in Section 5.5 should be attempted and the battery capacity should be retested.
6. If the battery delivers less than 50% of its rated capacity, it should be replaced. However, the user should determine the amount of capacity needed for their particular application and adjust the pass/fail threshold accordingly.

NOTE: The above procedure should be performed by an experienced battery maintenance facility utilizing the proper charging and test equipment. For information regarding Concorde's recommended test equipment go to: Concorde Battery Aircraft Battery Accessories.


End of copy and paste......



In the case of the GPL-31XT it's 230 minutes.

How does that procedure sound?
Any suggestions for how I can achieve a constant load of 25A load for 230 minutes?

Then, how do I reconcile the time back into AH capacity? Surely it's not linear... I.e 115 mins = 50%.

[sailorboy1]

Originally Posted by neelie

Sailorboy1. You could be right. I've stopped using the inverter until I resolve the issue.

Has the refrigerator tripped out low voltage since then? Have you tried running the microwave off the inverter and the refrigerator at the same time when you were SURE the batteries were fully charged (or even at 80%)?

All this battery talk I feel is just confusing the issue. You don't have really have a battery "problem" (even if they have lost capacity it isn't the problem you started the thread about), you have some type of cable/connection problem or no problem at all (other than your batteries may have been a lot lower charged than you originally thought as that would cause your problem).

Heck the problem you started the thread with is how I know when my battery monitor has lost sync; when the voltages don't seem to match the displayed SOC.

[Maine Sail]

Originally Posted by neelie

Sailorboy1. You could be right. I've stopped using the inverter until I resolve the issue.

Mainesail or anyone.. Re Capacity test. Advice needed.

Lifeline documentation recommendation is as follows:

Copy and pasted.....below..



To determine the actual capacity of a Lifeline® AGM battery relative to its rated capacity, a full discharge test should be performed. Although there are various battery testers available on the market, such as carbon pile testers, impedance meters, conductance meters, and others, these testers are not reliable in determining the battery's actual capacity. To determine the battery's actual capacity relative to its rated capacity, use the following procedure:

1. Stabilize the battery at 68-86°F (20-30°C) for at least 24 hours.
2. Bring the battery to full charge as described in Sections 5.4, 5.5 or 5.6 as applicable.
3. Discharge the battery at a constant current of 25 amperes until the voltage falls to 10.5 volts (5.25 volts for a 6 Volt battery). Record the discharge time in minutes.
4. Compare the measured discharge time to the published 25A rating (reserve capacity minutes) for the battery.
5. If the battery delivers less than 80% of the rated capacity the conditioning procedure given in Section 5.5 should be attempted and the battery capacity should be retested.
6. If the battery delivers less than 50% of its rated capacity, it should be replaced. However, the user should determine the amount of capacity needed for their particular application and adjust the pass/fail threshold accordingly.

NOTE: The above procedure should be performed by an experienced battery maintenance facility utilizing the proper charging and test equipment. For information regarding Concorde's recommended test equipment go to: Concorde Battery Aircraft Battery Accessories.


End of copy and paste......



In the case of the GPL-31XT it's 230 minutes.

How does that procedure sound?
Any suggestions for how I can achieve a constant load of 25A load for 230 minutes?

Then, how do I reconcile the time back into AH capacity? Surely it's not linear... I.e 115 mins = 50%.

The RC test is a good test when batteries are new and the 20 hour Ah capacity and 25A RC load minutes line up well.

As batteries sulfate/age the 20 hour test is a lot more reflective of the loads we use on board and gets you a better approximation of actual usable capacity at your average loads.. Most boaters draw the batteries at considerably less than the 20 hour rate. Either test can be performed but as batteries age the RC test and 20 hour test will yield slight differences. Don't know why but I have tested this many times and found these irregularities.

One reason the Ah test is perhaps more appropriate, for a deep cycling application, is because there is no reconciling and you use the Ah counter to show you exactly how many Ah's were produced before the battery hit 10.5V.. I just did a capacity test today, on a prototype of an AGM that will be on the market soon. The recommended procedure for capacity was a 20 hour test.

Small incandescent light bulbs or resistors can be switched on and off to get the desired load and maintain it, if you do not have a constant load device, which 99.99% of boaters will not. Hold it as steady as you can and you will get close enough results.

An RC test can work, certainly better than a capacitance tester with no baseline, but you may find that it says you have less than you really do when compared to a 20 hour test. This is because the 20 hour test is more reflective of the loads at which we remove capacity from the batteries on cruising boats..

[hellosailor]

"Any suggestions for how I can achieve a constant load of 25A load for 230 minutes?"

You'd need about a 300W load for that test. Anything simple, like "12" volt light bulbs that draw 300 watts. You could buy three 100W halogen headlight bulbs, hook them up in series and use them for the load. Or scrounge six old headlights, folks usually throw out the old dual-filament bulb when the low beam has failed, so the dumpster behind the auto parts store may have several with good high beams that are 50-65W each. There are other ways to scavenge a load but buying some 12v spotlights or bulbs is probably the simplest cheapest quickest way to do it.
Or a 300W 12v cabin heater? Something that you can use afterwards?

[neelie]

Originally Posted by sailorboy1

Has the refrigerator tripped out low voltage since then? Have you tried running the microwave off the inverter and the refrigerator at the same time when you were SURE the batteries were fully charged (or even at 80%)?

All this battery talk I feel is just confusing the issue. You don't have really have a battery "problem" (even if they have lost capacity it isn't the problem you started the thread about), you have some type of cable/connection problem or no problem at all (other than your batteries may have been a lot lower charged than you originally thought as that would cause your problem).

Heck the problem you started the thread with is how I know when my battery monitor has lost sync; when the voltages don't seem to match the displayed SOC.

No fridge does not trip out at all. It has only ever tripped out when there has been a large current draw.

Fridge does not trip out unless SOC is not near full... I won't say a number but, say it's about 150-200 shy of being full.

But when the sparky was on board to test the batts, we used the microwave as the load. And no tripping, but then, I was confident of being close to 100% as charge rate 5 hours earlier had dropped to about 4A.

Of course, wiring may be an issue, but the boat is 7 years old and has been extremely well put together with amazing attention to detail. There is zero corrosion evident. Everything is bone dry.

[sailorboy1]

you don't have a problem other than a normal voltage drop under a large load, stop worrying

[chala]

Originally Posted by hellosailor

"Any suggestions for how I can achieve a constant load of 25A load for 230 minutes?"

You could buy three 100W halogen headlight bulbs, hook them up in series and use them for the load.

Series?

[Wotname]

Originally Posted by chala

Series?

Yep, they are the special 4.4 Volt version...

[chala]

Originally Posted by sailinglegend

And for those who want to go for Lithium batteries then they need to be another ten steps higher up the knowledge ladder.

I do not see it that way. Lithium batteries for portable electrical tools have proven to be reliable and easy to use. The tools stop when the battery needs charging. The charging is a simple affair of waiting until a flashing indicator light turns to permanent or whatever. An indication that the battery is near the need of recharging would be an improvement so would be an indication of the capacity of the battery.

Originally Posted by Ex-Calif

My AGMs are "Delco Marine" whatever that means and,

Did you ever try to charge them with AC Delco I-70nn (11 to 15, 6A to 40A) fully Automatic Battery Charger? Also a very simple tool to use to fully charge a battery.

Originally Posted by sailinglegend

Your 0.6v drop through an isolator switch

In fact this is.

Originally Posted by neelie

As for total voltage loss, there was another 0.6V lost in the 12 feet of 4/0 cable running through a battery switch did not help either.

Originally Posted by neelie

According to the electricians calculations, a draw of 180A will result in approximately .5V drop over 12 feet.

So the voltage drop through the isolator switch is 0.1V if it is? Also 0.5 V drop over 12 feet seems to me to be on the high side I would think that at 77F the figure should be closer to 0.12V

A 0.6V drop at 180A will produce 108 W, a noticeable amount of heat in a small switch enclosure if held for 3 minutes.

[Ex-Calif]

Originally Posted by chala

Did you ever try to charge them with AC Delco I-70nn (11 to 15, 6A to 40A) fully Automatic Battery Charger? Also a very simple tool to use to fully charge a battery.

No but I have a Promariner 1240P on the way as part of my upgrade project.

I know I will be upgrading the battery bank at the end of this as well. haven't decided what I am going to do yet except try to get 400 a/h squeezed in there somehow.

[sailinglegend]

Originally Posted by chala

.....A 0.6V drop at 180A will produce 108 W, a noticeable amount of heat in a small switch enclosure if held for 3 minutes.

A high voltage across a switch is quite common, especially if the switch us not used much to isolate a load. My service battery switch may get switched off once a year so we built up a 0.25v drop due to contact dirt at only 15 amps. A quick an easy clean and the volt drop went down to 0.01v. Now we switch it on and off at least once a month to try and keep the contacts clean. Many isolator switches build up contact burning because they are not designed to take high currents, or they have been installed incorrectly. I have seen a 500 amp bow thruster isolator switch wired in series with a 30 amp master battery switch instead of directly to the battery. This caused the battery switch to melt and the boat finally lost all power!

[hellosailor]

Thanks, Chala. I knew someone was hacking into my computer and tampering with my messages. That proves it. Obviously should have been "parallel". (G)