Voltage Drop in AGM Under Load?

[smac999]

is that voltage at the batteries, at the inverter terminals, or at the compresser terminals?

that seems low to me. I generally set inverters to shut off at 10.5v

running a microwave with an ~800ah bank I think I normally see more in the mid 11's but I can't recall off hand.

[sailorboy1]

Originally Posted by neelie

Just thought that it would be too long before I got a chance to deplete the batteries to 80% SOC to get the same condition as before

So in the interest of science, I brewed 2 cups of tea. Here are the results at 90% indicated SOC

Load 5A; V = 12.5
Load 180 A; V = 10.6

1.9V seems a big drop under these circumstances.

I'm back to thinking it's one of two things. A dead battery or I should have got LFPs.

And lastly, to Bianka - I wil place my Amazon order for those 2 battery testers. Thanks for the advice!

And what did the voltage go back after the 180A load and how many amp-hours did you use (you say you have a BM)?

I brewed coffee this morning.
started at -35AH and 12.6 volts (because the solar was putting in a little)
during at -90 amps voltage went to 11.5
after voltage went back to 12.6 and amp-hours were -45

I'm not sure you really have a problem.

[neelie]

Voltages measuered via multimeter were at freezer compressor power terminals on the compressor.BMS and inverter indicated voltage were also within 0.1V.

So not much in the way of losses in the wiring.

Voltage went back to 12.5 after a couple of minutes,cant recall the AH used but SOC went down by about 2% .. indicating about 15AH used.

[Maine Sail]

Here are a couple of data points:

I was just in the shop and have an AGM battery on my test bench that I am doing some marine specific testing on for a battery manufacturer. I figured this would be a good time for another test.

Battery = Group 31 AGM - 110Ah Tested Capacity

*Battery has had 7 complete 20 hour discharge capacity tests and about 35 cycles to 80% DOD plus about another 15 to 50% DOD.

*Battery finished 10 days of sitting at 20% SOC last Thursday in a room with temps well over 100F during the day. This battery is being purposely treated like many boaters do, abusively...

*I charged it to full Friday afternoon.

*Today I discharged it to 90% SOC (controlled test equipment so I know for a fact the battery was at 90% SOC)

*I then applied a .91C load or 100A to this 110Ah battery

*I let it run for 12 minutes at 100A with no break

*Lowest terminal voltage was 11.49V (NIST Calibrated Fluke DVM)

*On another note I am still using an 8 year old wet cell Group 31 deep cycle battery and 2000W inverter to power my heat gun on customers boats or in boat yards or at mast racks where power is not available (beats a generator). Each shrink takes about 45-60 seconds and I do upwards of 20+ on some days.... Granted the battery gets a rest in-between but the darn thing is 8 years old and still dishes out well over 100A without barfing... A .25C load killing a 750Ah bank of Lifelines? Not good and no, certainly not normal....


Lifeline batteries really need to be charged at high charge rates as often as possible. If continually charged with low "C" rates it can cut into cycle life. They also need to be equalized periodically depending upon your use..

Lifeline batteries are not "full"/ 100% until net accepted current is 0.5% of Ah capacity at 14.4V..

You need to stop trusting your Ah counter, it is not even programmed correctly, and start doing manual resets when "known full" parameters have been met. Your Ah counters SOC screen is wrong as you have a Peukert of 1.25 programmed into it.. Solar and "auto synch" with an Ah counters simply does not work well....

Know full:

Battery terminal voltage = 14.4V
Net accepted current = 0.5% of Ah capacity

[neelie]

MaineSail.. Many thanks! You're a legend!

I'll keep an eye out on when the solar reaches its float stage and see what the voltage and Amp are. If they meet your criteria, I'll do a manual sync.

Ive thought about tinkering with the Peukerts exponent but the batteries are only 8 months old and have never ever been below 70% SOC. So I thought factory number of 1.25 would pretty much suffice. Clearly not.

I am reticent about discharging to any less than 70% SOC in an effort to keep the cycle life up.

My original plan was to Lithium, but I ran out of time to implement it, so went the easy route with LA. None of this madness would occur with LFPs. So I had the Lifeline GPL-31XTs installed ( Lifeline Batteries - Marine & RV Deep Cycle Batteries) . FYI.. LFPs would not have cost significantly more!

I'll order one of those Balmar BMS that you recommend.

Thanks

Niels.. (ex Hong Kong)

[Maine Sail]

Originally Posted by neelie

I'll keep an eye out on when the solar reaches its float stage and see what the voltage and Amp are. If they meet your criteria, I'll do a manual sync.

No...>>!!!!!!! The amperage to determine full needs to be at ABSORPTION VOLTAGE..... Many chargers, regulators and controllers go into float far to early and often require a reboot to go back into absorption voltage..

Originally Posted by neelie

Ive thought about tinkering with the Peukerts exponent but the batteries are only 8 months old and have never ever been below 70% SOC. So I thought factory number of 1.25 would pretty much suffice. Clearly not.

If you want your SOC screen to be even close to any level of accuracy the Peukert should be programmed for 1.12 for Lifelines. Is this 100% perfect? No, but it is the best you can really do.

Originally Posted by neelie

I am reticent about discharging to any less than 70% SOC in an effort to keep the cycle life up.

Shallow cycles do lead to longer life but with Lifeline AGM's getting to 100% as often as possible, proper float voltages, equalizations and high charge rates are also important to the longevity..

Originally Posted by neelie

My original plan was to Lithium, but I ran out of time to implement it, so went the easy route with LA. None of this madness would occur with LFPs. So I had the Lifeline GPL-31XTs installed ( Lifeline Batteries - Marine & RV Deep Cycle Batteries) . FYI.. LFPs would not have cost significantly more!

I'll order one of those Balmar BMS that you recommend.

Thanks

Niels.. (ex Hong Kong)

[/quote]

LFP is not perfect yet either...

[smac999]

Originally Posted by Maine Sail

*On another note I am still using an 8 year old wet cell Group 31 deep cycle battery and 2000W inverter to power my heat gun on customers boats or in boat yards or at mast racks where power is not available (beats a generator). Each shrink takes about 45-60 seconds and I do upwards of 20+ on some days.... Granted the battery gets a rest in-between but the darn thing is 8 years old and still dishes out well over 100A without barfing... A .25C load killing a 750Ah bank of Lifelines? Not good and no, certainly not normal....

holy you carry a battery and inverter around?... I don't even use guns when I have power as it's more work pulling a cord all over the boat.

time for a butane torch. the big anchor ones are great.

[Maine Sail]

Originally Posted by smac999

holy you carry a battery and inverter around?... I don't even use guns when I have power as it's more work pulling a cord all over the boat.

time for a butane torch. the big anchor ones are great.

Yep much easier than 600 feet of extension cord or a generator.. I have tried about 10 or 12 torches including multiple ceramic element models specifically intended for heat shrink and the only time I will use one is in an emergency.. Proper shrinking and even melting of the adhesive really requires a heat gun and I won't cut corners on that so yes I carry a batt & inverter for certain situations...

[chala]

Originally Posted by SailorHarry

DIRECTLY at the terminals of each AGM in your battery bank, both before and during drawing maximum current.

Originally Posted by neelie

a) 6 batteries in parallel - surely once there is load on them, the voltages will be the same across each terminal....or not?

Originally Posted by colemj

Checking at the terminals won't be helpful unless the batteries are electrically isolated from each other first. This will involve removing some of the connectors.

“during drawing maximum current”
A battery not contributing to the load (bad connection) will show up with a comparatively higher voltage( no discharge). Also a battery not getting charged (bad connection) will show up with a comparatively lower voltage (not charging).

Originally Posted by neelie

Note : These AGMS are pampered .. SOC is never less than 70% and they're floated to 100% at least twice a week.

Not sure about pampered.

Originally Posted by neelie

I'll keep an eye out on when the solar reaches its float stage and see what the voltage and Amp are.

Any result of the voltage taken at the terminals of each battery?

Are you familiar with Victron FLP?

[neelie]

Chala: thanks for the clue regarding checking voltages.

No idea what Victron FLP is.

Just arrived Grenada.. We're here for 3 months so will get back into trouble shooting next week after finding rigger and sailmaker to get other stuff done.

Personally, I'm starting to think there is no problem - it's just a "feature" of lead acid batteries.

Balqon have 9kw (700AH ) packs for $3500 .. That's almost what my useless Lifeline 750Ah AGMs cost.

[chala]

Originally Posted by neelie

No idea what Victron FLP is.

Victron Energy manufactures a complete sytem using Lifepo4 battery that may do exactly what you need. http://www.victronenergy.net.au/uplo...ine_EN_web.pdf and other related documentation. May save you reading 3800 + replys.

[hellosailor]

neelie-
FWIW battery capacity is typically rated at 1/20th C, and it decreases significantly as you go to higher discharge rates. For instance, Lifeline says your batteries are each good for 105 hours at the rating for the 20-hour rate, but 688 hours at an 8-amp draw. (i.e. about a 65 hour rate). A sixfold difference!
The also suggest not more than a 50% charge cycle, based on 1000 cycles at 50% and cutting that in half to 550 cycles at 80%, with an express warning that they simply are not designed for 100% cycling. There's a whole technical manual at
http://www.lifelinebatteries.com/manual.pdf
for them. I don't think anyone disagrees with their claims to make the best AGMs in the business and would suggest contacting them directly. It could be that your chargers are simply not matching the voltages that Lifeline needs--everyone has different maximums and optimums and if you don't have temperature correction, the voltages are guaranteed to be wrong most if not all of the time.

Batteries are "physics" and repeatable science. If something isn't behaving as expected, or isn't behaving as well as other installations, there's usually something simple but subtle that's wrong.

[neelie]

Chaka.. Ah ha! You mistyped, you meant LFP. And of those 3800, about 10 were mine. I actually built a 100AH battery to teach myself lithium. And I LOVE it.

Hellosailor: thanks for your advice. But earlier, I stated that batteries never go below 70%. The bulk and absorb voltages on all chargers and controllers are set as stated on the batteries. And the voltage as indicated on the BMS concurs.

90% of the time the batteries are floated by the PV array via a. Midnite Solar Controller (this is about as top end as one can get, Made in the USA!!.. No less! And yes, temperature controlled to boot!)

Let's try and remember this is a cruising sail boat not some sterile, perfect laboratory. Batteries are just pieces of working equipment, they are not some fragile delicate Faberge eggs. Surely, they must be capable of handling tolerances?

As far as I am concerned, I have done everything possible to ensure that these tolerances are as minimal as possible.

Now regarding temp control, I only gave one sensor for each charge source. In my books, that's next to useless. I need to be sensing temperatures in every battery, if not every cell if temp sensing is as significant as they say.

Next week, I will uproot the mattresses, get to the batteries and charge them at 200A and check the temperatures and voltages at each battery.

I still think Lead Acid is the work of Satan. Lithium would not give me these issues.

[Stu Jackson]

Originally Posted by sailorboy1

I don't about about AGMs, but my 460AH 6V golf cart batteries are probably designed for a large load and under a 100 amp load the voltage will drop from 12.5 to 11.5 if the batteries are at 95% SOC.

This is from page one of this thread.

Of course this happens. We have a Freedom 15 I/C and the house bank voltage does this ALL THE TIME when the inverter is running the microwave.

What's so unusual?

In addition, Maine Sail and others have described why.

Have you ever read this that applies to your battery monitor?

For everyone installing a battery monitor: The "Gotcha Algorithm" thread, a "MUST READ"

Link-series Charging Algorithms -- The "Gotcha" Factor!

DEFAULTS are factory settings that are made to be modified to suit your setup.

Including your Peukerts factor, very important.

This is yet another reason why Maine Sail keeps repeating that going into float is NOT the way to deal with fully charged.

[hellosailor]

Neelie, when you say the voltages are set, just to clarify, do you mean "Set to AGM" on the devices? Or do you mean "set or programmed to the exact voltages specified by the battery maker" ? I ask because some AGM settings (i.e. Genasun) and some battery settings (Deka's AGM) simply do not match up.

When you've only got one thermal sensor, the procedure is to either bury it in the middle of the bank, where things presumably are hottest, or attach it to the main positive terminal, since the "most positive" end of things usually would be the hottest during charging. The idea is that either way, it is sensing the hottest point in the bank while charging, and your charging will be cut back to prevent thermal damage. (The rest of the system typically will still be within the optimum charging range.)

If you wanted to be certain of picking the right place for the thermal sensor, get a cheap no-contact IR thermometer and snoop around the batteries, see where the hottest points are during charging.