Trojan T-105 voltage under load

[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

[conachair]

Something not right there, below is the same setup cycling on solar with probably 2A - 6A loads overnight, you can easily see the fridge turning on and off. Round bout 80% state of charge in the morning.
Sure the voltmeter is accurate? What specific gravity are they at?

[transmitterdan]

What are the voltages of each battery after resting with no load for 2 hours? My guess is one of them is different than the other.

[Sam the Sailor]

Thanks! Voltmeter should be accurate. I'm using Nasa BM-2 for voltage, amps and to integrate amp hours. MyTriStar solar panel controller and handheld multimeter give similar readings than BM-2.

I need to check the specific gravity.

[smac999]

As a guess based on doing c20 tests a few times on other batteries. . They should stay over 12.5 for 5-6 hours and over 12v for 10-12 hours. With a c20 load.

You have something wrong.

[masonc]

Here's the datasheet, use this for your information.
https://www.trojanbattery.com/pdf/da...ata_Sheets.pdf

Trojan batteries have lower voltages that other batteries. I have 8 x IND17 running my house right now. You would be better to get a refractometer and measure the density of the electrolyte, it's $24. Compensate for temperature.
https://www.amazon.com/Ade-Advanced-...+refractometer

I would cycle the batteries for a few days, let them cool for four hours, disconnect all load and charging sources, and measure the temp and voltage. Measure each battery, with the strings disconnected. You don't need to disconnect the battery as long as there is no circuit.
Then report back the readings in table form.

[wrwakefield]

Sam,

We also have a house bank of T-105 batteries. You are right, what you are experiencing indicates something is not right...

Here is the T-105 spec sheet. Note, that depending upon the battery temperatures, you were likely undercharging them [Absorption = 14.82VDC @ 77F; more if cooler...]

I would make sure they are fully charged and the the wiring is good [connections, sizes, etc.] before assuming there is an issue with the batteries themselves [assuming they are new...]

Also, lead acid batteries don't reach their full potential until discharged a few cycles. And you may need to run an equalization cycle to get them up to capacity depending upon their charge history. [We equalize whenever they go more than a week in a partial state of charge (SOC) state.]

Best wishes sorting it all out.

Cheers! Bill

[donradcliffe]

Are the measured voltages at the panel or at the battery terminals? Could be some undersized or funky wiring involved. I was checking out a new Jeanneau this week and found the panel meter reading 12.1 v under a 10 amp load, while there was still 12.5 v across the battery terminals.

[sainted]

Originally Posted by conachair

Something not right there, below is the same setup cycling on solar with probably 2A - 6A loads overnight, you can easily see the fridge turning on and off. Round bout 80% state of charge in the morning.
Sure the voltmeter is accurate? What specific gravity are they at?

What tool provided that chart? Want one.

Scott

[SFord]

I'm not an expert and this is what I learned many years ago. When batteries are used either in parallel or series it is best to try and acclimatize them to each other with multiple charge discharge cycles in parallel preferably in a temperature controlled bath. New high quality batteries were seasoned in this way before being connected in an emergency critical application power back-up system. This may be why performance improves over repeated cycling. FWIW YMMV

Unfortunately I have no sources to cite and the EE that designed this system is no longer with us.

[sailorboy1]

This morning I got up and my 460AH bank of T105s was -85AH and was discharging at about 5 amps and the voltage was reading 12.3. The bank was close to fully charged yesterday.

This is a normal reading on the boat was the same as the Deka house bank I had prior.

[conachair]

Originally Posted by sainted

What tool provided that chart? Want one.

Scott

It's a raspberry pi running openplotter >
https://docs.sailoog.com/openplotter-v1-x-x/

With a ADS1115 voltage sensor >
https://www.ebay.com/sch/i.html?_fro...s1115&_sacat=0

The a built in prog called node red makes it pretty easy to create funky dashboards and graphs. Records everything to a database as well once a minute.

Great to spot anomalies that you just wouldn't see looking at a meter now and again.

[a64pilot]

Originally Posted by donradcliffe

Are the measured voltages at the panel or at the battery terminals? Could be some undersized or funky wiring involved. I was checking out a new Jeanneau this week and found the panel meter reading 12.1 v under a 10 amp load, while there was still 12.5 v across the battery terminals.

I think this is very likely true, plus accuracy of the measuring device.
I do not think I have inadequate or funky wiring, but my BMK on my Magnum which is connected directly to the bank is reading 13.4 V.
My Blue Sea M2 multimeter which I connected to the backside of the battery switch for ease of installation is reading 13.2 V.

[Sam the Sailor]

Originally Posted by donradcliffe

Are the measured voltages at the panel or at the battery terminals? Could be some undersized or funky wiring involved. I was checking out a new Jeanneau this week and found the panel meter reading 12.1 v under a 10 amp load, while there was still 12.5 v across the battery terminals.

The voltage is measured from the battery terminals so undersized wiring or bad connectors shouldn't affect if I'm right (unless it's the battery terminal connection).

[Sam the Sailor]

Originally Posted by transmitterdan

What are the voltages of each battery after resting with no load for 2 hours? My guess is one of them is different than the other.

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.