Expected voltage sag?

[ewarnerusa]

I've got two 6 volt GC batteries. I have an inverter just powering a laptop. It's pulling under 100 watts AC. What kind of voltage sag would you expect that to put on these batteries if they were fully charged? What would the voltage read across the battery posts?
Thanks.

[westend]

I'd definitely get out the baking soda and some hot water. Give the battery tops and terminals a good bath. Let dry and then cover the terminals and exposed cable ends with dielectric grease or a terminal spray.

With that much oxidation going on, I might put a penny under the cables and/or punch some holes in the case lids for air exchange.

[ewarnerusa]

I tried testing the PVC lid with the multimeter as you suggested and got a flickering from the meter. It never exceeded 0.1V.

I repeated my laptop overnight test, although I've picked up a 12V power cord for it since the last time and that is what I used. Before bed the voltage was 12.4V. This morning it was 12.2V and returned to 12.4V when I unplugged the laptop charger. Outside temp is just above freezing at 35F.

[MEXICOWANDERER]

Put honorable meter negative probe on negative post. Put positive probe tip anywhere on the PCV lid of the battery. Do you get a voltage reading? If yes the lid is polluted with electrolyte. Wet between the cells is a nice short both n distance and effect. Adds up during months of disconnected storage.

This has yet to be discussed but sprinkling a little baking soda on the lid between cells is an excellent preventative measure. Four months 5 ma = 14.4 amp hours needless discharge and a disconnect switch does not do a thing to prevent it.

[ewarnerusa]

Beautiful blues and greens?
OP update:
I opened up the battery cases today and found that the corrosion was back, this time in lovely green to go along with blue. I cleaned all that gunk off and scraped things with a pocket knife and sandpaper until I had nice gleaming metal at all the connections. I also cleaned up my ground connection to the frame. This seems to have addressed the voltage drop, with the panels off and inverter on with the same laptop charger load of just under 100 watts I'm only getting a small voltage drop. It seemed to level out at around 12.4V. Once again, voltage measurements are taken right at the posts via the SCC voltage sense wires. I dipped the hydrometer in each cell and the readings were all right around 1.300 with panels disconnected. Does that seem OK? Seems too high, although the SCC was in float when I started the maintenance. Anyway, we'll see how things go now with cleaned up connections.

First battery in series, lovely greens and blues:


Close up of the green gunk:


Second battery in series:


Cleaned up:

[westend]

A dip with the hydrometer might turn up the culprit. At the least, it will show that all the cells are fully charged.
If you've been nursing them along and they have solar every day, it would seem that the batteries should be OK.

How long did they sit uncharged?

[pianotuna]

Hi Chandalen,

That depends on the load, and size of the battery bank. For example my 3000 watt inverter draws 300 amps when running flat out. That taxes the 556 amp-hours of AGM batteries--so there is voltage drop far in excess of 0.1 volt. The wire is correctly sized for 300 amps.

Chandalen wrote:

Anything more than 0.10v is too much.

[/quot]

[Chandalen]

#1 reason for voltage drop (besides load) is wires are too thin.

You need to measure the voltage on the batteries under load AT the batteries, then measure at the inverter. The difference is your voltage drop. Anything more than 0.10v is too much.

This is a great calculator.

http://www.calculator.net/voltage-drop-calculator.html

13.5 is a typical fully charged battery, 10.5 is the kiss of death for a battery.

[ewarnerusa]

Laptop is a Dell XPS and the charger is rated at 90 watts. Kill A Watt confirms that. It read 90 watts in the evening and in the morning, so I assumed that's what it did all night, too. It is over 6 years old on the original battery.

[CJW8]

The OP's (new) 232 amp hour batteries could be in the ball park of 200 AH now. Maybe less. So pulling 90 AH over night could put him in the 60-70% range or about 12.3 V measured with no load.

The sag is too much but the voltage seems reasonable in the morning.

I'm wondering why his laptop is pulling 90-100 watts all night. Is his laptop crunching numbers all night? It seems when his laptop battery gets full his usage should go down.

[Boon_Docker]

..

[Boon_Docker]

:S

Quote from Page 1 Post #6

ewarnerusa wrote:
My batteries got hammered pretty bad last season while the trailer was in the shop. Solar was disconnected and batteries were deeply discharged. I suspected they were shot but I've tried nursing them back with equalizations and being maintained with temperature corrected 14.8V charging profile. But I think they're damaged. After a full day charge, the inverter draw alone with the laptop charger will drop the voltage to 11.6V and hold steady. The voltage will often recover back to 12.5+V even after running this load for a while. Voltage reading is coming from the SCC voltage sense wires at the battery terminals.

[red31]

ewarnerusa wrote:
So capacity seems unaffected

Not sure why you believe this, your inverter 'load' test indicates something different.

Yep, you asked a simply question which which I have no info to share but your sag seems excessive to me.

[2oldman]

SoundGuy wrote:
Sorry, nope. Your post which includes the link to the other discussion in which the OP indicated his batteries may be toast is Post #19 in this thread and yes it is on Page 2 of this discussion.

We must be talking about two different things.

The link in THIS thread which I provided (post 19), which YOU quoted, links to post #6 in this thread. You must be talking about something else. I have not linked to any other discussion thread. Someone else did that.

SoundGuy wrote:
.. he never said anything about this in any of his previous posts in this thread...

We know that's not true.

[SoundGuy]

SoundGuy wrote:
Sorry, but until you yourself provided a link to another discussion in which it was evident the OP's batteries are most likely pooched anyway he never said anything about this in any of his previous posts in this thread which I did read.

2oldman wrote:
I don't think so. The link I provided is on Page 1 of this thread. :S

Sorry, nope. Your post which includes the link to the other discussion in which the OP indicated his batteries may be toast is Post #19 in this thread and yes it is on Page 2 of this discussion. :S :S

[2oldman]

SoundGuy wrote:
Sorry, but until you yourself provided a link to another discussion in which it was evident the OP's batteries are most likely pooched anyway he never said anything about this in any of his previous posts in this thread which I did read.

I don't think so. The link I provided is on Page 1 of this thread. :S