Trojan T-105 voltage under load

[Sam the Sailor]

Originally Posted by noelex 77

The voltages you are reporting are not promising.

Are you sure the readings are acurate? Voltage measuring instruments can easily drift out calibration, especially on boat with salt, heat, vibration etc.

I think the voltage readings are quite accurate. My all three meters show approximately same values (Nasa BM-2 battery monitor, TriStar solar panel controller and handheld multimeter).

[Maine Sail]

Let the batteries break in then re-test. This means a number of deep cycles, 7-25+ followed by full recharges. This is not totally uncommon for deep cycle batteries when they are new.

[Sam the Sailor]

Originally Posted by Maine Sail

Let the batteries break in then re-test. This means a number of deep cycles, 7-25+ followed by full recharges. This is not totally uncommon for deep cycle batteries when they are new.

Thanks for the advice! So no need to worry about the 0.3 V difference between the batteries for now? I don't have adjustable power source and probably won't ge one soon so I cannot equalize/charge the 6 V batteries individually.

Br,
Sam

[john61ct]

Do what you can for now, get better gear when you can.

Heavy loads like a windlass will bring V down a **lot** below those theoretical V vs SoC charts, maybe need more than 24hours to get to actual resting point.

Have you got an AH counting meter? Using that to estimate SoC will be more accurate than measuring voltage.

[Mark Johnson]

Originally Posted by Sam the Sailor

Hi,



I just installed two Trojan T-105 batteries in series giving me 225 Ah @ 12 V. I charged them fully keeping 6 hours at 14,5 V absorption voltage and during last 3 hours batteries took under 1 A.



However, after charger was disconnected battery voltage was soon 12,3 V under 2 A load and 12,0 V under 8 A load. At that point only 12 Ah was used from the fully charged batteries. Is that normal? For me the voltages seem much lower what they should be.



I tried to search C20 (i.e. 225/20 = 11 A) voltage vs time curve to see what I should be expecting for T-105 batteries but couldn't find it. Is that kind of chart available somewhere?



Br,

Sam

Only “resting voltage” means anything at all!

If first FULLY charged, then all sources of power are disconnected for several hours... (going in or out), then the resting voltage should be just over 12.6V.

Because the battery bank’s V with a load on it tells you nada about the charge of the battery, a “charge monitor”, like Link 10, is required. These sophisticated monitors count the amps going in or out, and if you top up your batteries regularly, which re-zeros the meter, they are spot on accurate.

[noelex 77]

Originally Posted by Mark Johnson

Only “resting voltage” means anything at all!

The voltage under load is often a better predictor of battery health than the resting voltage.

It is not unusual to see a battery that has reached the end of its life, or has become defective, to have a normal resting voltage, but to also have a voltage drop much lower than it should do with even a small load.

In summary, resting voltage is a better predictor of a battery’s SOC, but voltage under load is better at showing if the battery is healthy.

A capacity test is better again for both of these parameters, but this test is much more involved.

[Mark Johnson]

Originally Posted by noelex 77

The voltage under load is often a better predictor of battery health than the resting voltage.



It is not unusual to see a battery that has reached the end of its life, or has become defective, to have a normal resting voltage, but to also have a voltage drop much lower than it should do with even a small load.



In summary, resting voltage is a better predictor of a battery’s SOC, but voltage under load is better at showing if the battery is healthy.



A capacity test is better again for both of these parameters, but this test is much more involved.

The post was in reference to state of charge in NEW batteries, and what V is normal for such new batteries.

It had nothing to do with the “health” of these new batteries, presumed to be normal, healthy, NEW batteries.

Testing the AH capacity = health, of older batteries, etc. is a very different subject.

Mark Johnson (Boatwright for > 50 years)
Delphys Marine

[noelex 77]

Originally Posted by Mark Johnson

It had nothing to do with the “health” of these new batteries, presumed to be normal, healthy, NEW batteries.

I don’t think that assumption is correct, Mark. I think Sam is worried the batteries, (or a single battery) is defective. I would be concerned about this given the reported voltages under load.

Originally Posted by Sam the Sailor

Even after reading the links it's not clear for me whether it's more likely balancing/commissioning issue or defect battery.

[transmitterdan]

Originally Posted by Sam the Sailor

I left the fully charged batteries disconnected for few hours and measured the voltages: both were 6.44 V which is what good batteries should show, I think.

So that is about full for new batteries. Go sailing.

[conachair]

Originally Posted by transmitterdan

So that is about full for new batteries. Go sailing.

Wouldn't you dig a bit deeper if your new 225Ah batteries soon went down down to 12.3v with a 2A load?

[transmitterdan]

They are at 12.88V. They can’t drop to 12.3V with 20AH drain. If one of the batteries was “bad” the voltages would not be equal. So it means there is a measurement error somewhere not bad batteries.

[transmitterdan]

Originally Posted by Sam the Sailor

Thanks for the advice! So no need to worry about the 0.3 V difference between the batteries for now? I don't have adjustable power source and probably won't ge one soon so I cannot equalize/charge the 6 V batteries individually.

Br,
Sam

Worry about the batteries being different voltage when they are at rest (not charging or discharging). If they are the same after doing nothing for couple hours then there is no imbalance problem. The difference measured when charging or discharging has more to do with cabling and your measurement technique I would guess. New batteries are often a little "different" in the early days.

As another poster correctly said, use them for a while and then see how equal they are at rest. Check each battery at-rest voltage and compare to the SOC chart made by Trojan.

I strongly suspect there is no problem here.

[john61ct]

Originally Posted by Mark Johnson

The post was in reference to state of charge in NEW batteries, and what V is normal for such new batteries.

It had nothing to do with the “health” of these new batteries, presumed to be normal, healthy, NEW batteries.

Yes they are new.

But whether they are defective or not is exactly the topic of the OP and what everyone else is discussing.

WRT your incorrect statement, even if a bank is perfectly healthy, a table of voltages under a given stable load will have a pretty stable correspondences to SoC.

Until the battery ages and loses capacity, then the relationship changes.

Just as it does with true resting voltages, after 24-72 hours.

[transmitterdan]

New batteries tend to have a lot of variance in voltage at 100% SOC. For example, my new Lifeline batteries measure 13.1V after resting for 7 days fully charged. But they will eventually follow the charts after a few months.

[rgleason]

Originally Posted by Sam the Sailor

Hi,

I just installed two Trojan T-105 batteries in series giving me 225 Ah @ 12 V. I charged them fully keeping 6 hours at 14,5 V absorption voltage and during last 3 hours batteries took under 1 A.

However, after charger was disconnected battery voltage was soon 12,3 V under 2 A load and 12,0 V under 8 A load. At that point only 12 Ah was used from the fully charged batteries. Is that normal? For me the voltages seem much lower what they should be.

I tried to search C20 (i.e. 225/20 = 11 A) voltage vs time curve to see what I should be expecting for T-105 batteries but couldn't find it. Is that kind of chart available somewhere?

Br,
Sam

I agree that these results are not acceptable for a new battery and I am finding a similar situation for my new T105 in series. The last set lasted just 3 years and I am going to try equalizing them, but recent experience after using a new set of Trojans is very disappointing!

In my thread on equalizing t105 there was a post with a good attachment about SOC and voltages while charging and while under load.