Battery checking

[Heckler]

Just checking my batteries. 8 years old now!
The first one figures are:
Fully charged off the charger after a couple of mins 13.60v. I then put a 25 watt bulb across it for 2 minutes to take off the surface charge and it went down to 12.6v then let it rest for 10 mins and back up to 12.76v So assume its fully charged.
I then put the bulb back on for two hours.
The immediate figures were 12.76v no load - 12.56v on load
An hour later it had dropped to 12.36v on load
An hour later it had dropped to 12.26v on load
Then when I took the 25watt bulb load off it went straight to 12.55v and after 15 mins had gone back up to 12.69v
On the face of it it looks OK?
A two hour two amp load had hardly touched it yet when that little load was on it was reading quite a low voltage. Any thoughts?
Stu

 

[lw395]

Does it still do what you need it to do?

 

[dom]

How big is the battery? Resting voltage tests are only a very rough estimate, but 12.26v suggests that c.40 per cent of capacity used by just 4Ah. Realistically, batt prob had it, if it had stayed there. But the bounce to 12.69v is good enough to make the test inconclusive. You need a bigger Ah test drain to be sure

 

[BabaYaga]

A two hour two amp load had hardly touched it yet when that little load was on it was reading quite a low voltage. Any thoughts?
Stu

Sounds pretty normal to me. It would be useful to know the total Ah of the bank, though.

 

[Heckler]

Sounds pretty normal to me. It would be useful to know the total Ah of the bank, though.

The bank is 4 times 110amp hr. I unhooked this one from the bank to test it because the magic eye was showing black. As it happened, when I unscrewed it it was covered in black cqck, I cleaned it all up. The level is slightly down in the cells, but plates covered, "sealed" but you can take the tops off and have done in the past to top up.
Stu

 

[Heckler]

Does it still do what you need it to do?

Out in the bay yesterday, left the instruments etc on, after a couple of hours when I started the engine the chart plotter went off with momentary low voltage.
So they are startin to fail I suspect.
Stu

 

[GHA]

What size bank?
2a load pulling the voltage down to 12.26v after just 2 hours sounds suspect, my 225Ah trojans take hours after sunset just to get back down to 12.8v with fridge and laptop and lights running.

What's the SG readings?

 

[JumbleDuck]

A two hour two amp load had hardly touched it yet when that little load was on it was reading quite a low voltage. Any thoughts?

Simply charging a tablet will pull my house batteries (2 x 60Ah) down to 12.4V ... it doesn't take much to have a big effect.

 

[Bobc]

Mine do exactly that Stu, and have done since they were new.

Nothing wrong there.

Bob

 

[GHA]

A graph.....

http://www.arttec.net/Solar_Mower/4_Electrical/Battery Charging.pdf

 

[Heckler]

What size bank?
2a load pulling the voltage down to 12.26v after just 2 hours sounds suspect, my 225Ah trojans take hours after sunset just to get back down to 12.8v with fridge and laptop and lights running.

What's the SG readings?

Just been to Carrefour in La Linea to buy SG one and some distilled water, its shut! LL has been in shutdown mode for a week with even Lidls closing!
Will get one tomoz and report back. We were discussing this a while back and I said to VicS, if the batteies are down a bit on distilled water, does the acid/liquid become more concentrated and distort the readings?
Sty

 

[Heckler]

A graph.....

http://www.arttec.net/Solar_Mower/4_Electrical/Battery Charging.pdf

So my single 120 amp hr battery, using a C100 profile (120/1.2 amps) and using the 25 watt bulb giving somewhere near ish! the 1.2 amp discharge rate, shows that after two hours we are near 40-50 percent discharged which means a bad battery! Given that we should only have taken out 3-4amps?
In actual fact the lamp could be seen getting visibly, not dimmer but less bright.

Stu

 

[GHA]

So my single 120 amp hr battery, using a C100 profile (120/1.2 amps) and using the 25 watt bulb giving somewhere near ish! the 1.2 amp discharge rate, shows that after two hours we are near 40-50 percent discharged which means a bad battery! Given that we should only have taken out 3-4amps?
In actual fact the lamp could be seen getting visibly, not dimmer but less bright.

Stu

Dunno just how accurate any graphs can be with batteries as there are so many variables, and determining state of charge from voltage alone isn't easy, can take nearly a day to stabilize.

But a 25W load getting dim and down to 12.26v after couple of hours doesn't sound like a confidence filling accumulator

 

[Heckler]

Dunno just how accurate any graphs can be with batteries as there are so many variables, and determining state of charge from voltage alone isn't easy, can take nearly a day to stabilize.

But a 25W load getting dim and down to 12.26v after couple of hours doesn't sound like a confidence filling accumulator

Indeed. Will get a hydrometer tomoz and give that a go and do the same test on the other three batteries
thanks for that graph and link, was really helpful.
Stu
PS where are you now?

 

[Heckler]

Just checking my batteries. 8 years old now!
The first one figures are:
Fully charged off the charger after a couple of mins 13.60v. I then put a 25 watt bulb across it for 2 minutes to take off the surface charge and it went down to 12.6v then let it rest for 10 mins and back up to 12.76v So assume its fully charged.
I then put the bulb back on for two hours.
The immediate figures were 12.76v no load - 12.56v on load
An hour later it had dropped to 12.36v on load
An hour later it had dropped to 12.26v on load
Then when I took the 25watt bulb load off it went straight to 12.55v and after 15 mins had gone back up to 12.69v
On the face of it it looks OK?
A two hour two amp load had hardly touched it yet when that little load was on it was reading quite a low voltage. Any thoughts?
Stu

UPDATE
I started the same test on the 68 amphr starter battery which is usually left on line with the house bank. Same voltages to start then 10.55 v after half an hour! Tried to start on it with the predictable chatter from the starter solenoid. So at least we have found one bad un!
Makes sense now, the starter uses the dedicated one first in line, after standing for a couple of hours at anchor with the bits switched on, it has been going down and then the house bank has been going through the BOTH link AND the NASA shunt to start it and dragging the chart plotter voltage down.
Off to Carrefour now for a new one!
Stu

 

[Heckler]

UPDATE
I started the same test on the 68 amphr starter battery which is usually left on line with the house bank. Same voltages to start then 10.55 v after half an hour! Tried to start on it with the predictable chatter from the starter solenoid. So at least we have found one bad un!
Makes sense now, the starter uses the dedicated one first in line, after standing for a couple of hours at anchor with the bits switched on, it has been going down and then the house bank has been going through the BOTH link AND the NASA shunt to start it and dragging the chart plotter voltage down.
Off to Carrefour now for a new one!
Stu

Update
did a 12 hour motor day before yesterday, funny smell, checked house batteries, whoo, one was literally boiling steam out of the vent. Two others were hot and one was cool. Bearing in mind I filled with distilled water the other day. The Sterling really gave them a work out. Anyway, took the boiler out of circuit, disconnected the Sterling alternator booster and have just done a 36 hour motor from Almerimar to Gib, hot sticky, hardly any wind and found out that there is a 2-3 kt eastern bound current from Gib! The other 3, one kept cool, the other two got very warm. We made it here and tomoz, Carrefour again!
Stu

 

[Jabs]

Hi,

I did a test yesterday. 92 amps for an hour. Voltage under load fell from 12.4 to 11.9.

540aHr bank.

Does that sound reasonable??

Thanks

Tony.

 

[ghostlymoron]

92ahrs is 17% of your capacity so 0.5v drop sounds ok to me.

 

[Juggler7823]

Hi Stu,
Sorry to hear of your battery problems,
Discharging lead acids to below 12V will reduce the lifetime considerably.
Roy