Whats normal voltage drop from a 4amp load? (210ah)

[wopachop]

I have two brand new 6v from costco. I pulled 20amp hours out of them a week ago and then fully charged with an automotive battery tender.

Today i put a 3.8a load on them and voltage is down at 12.15v after a few minutes.

Are they supposed to sag that much under a little 4amp load? Did a quick search and all im seeing is topics about voltage sag while under solar power. My batteries are on the garage floor.

edit: I should have checked early. My watt meter is saying 12.15v.

But 2 multimeters are saying 12.27v and 12.3.

[wopachop]

shastagary wrote:
why are you worried about using your 10amp charger

Im asking a question about voltage drop.

[wopachop]

Yo MDK!!! There are 3 brilliant new replies.

First dude quotes my spelling error. I noticed it after posting but didnt edit. I knew someone would have to hop on that easy one.

Second guys doesnt understand my data.

Third dude is a repeat of not understanding the original question.

[shastagary]

why are you worried about using your 10amp charger on your batteries most cars now have over 100amp alternators that charge the car battery and the golf cart chargers your batteries are meant for are way more than 10amp chargers.
your 10amp charger will not charge at a full 10 amps continuously once the batteries reach full charge the charging current will drop.

[Gdetrailer]

wopachop wrote:
I got to take some of the blame as it happens to me a lot on forums. I write big long confusing posts and some people dont absorb it correctly. It seems like time2roll followed along just fine. While others are yelling at me saying 12.64v is not fully charged. I was hoping we all agreed im closer to 90% charge from the 5a battery tender and the main question of the thread is should a 4a load make the batteries drop to 12.4v?

Umm, hate to tell you but THAT is not the way you go about checking your battery capacity, hence the posts TELLING YOU THIS..

You START WITH A FULLY CHARGED BATTERY.

You don't start with a PARTIALLY DISCHARGED BATTERY AND GUESS WHAT THAT PART OF THE DISCHARGE IS AT THAT POINT IN TIME.

For instance, I just checked a group 24 battery that I use in an antique auto. I had recharged that battery a couple of weeks ago FULLY.

That auto does not have an alternator or generator to recharge the battery.

I have run that auto for about 2 hrs over the last two weekends.

That battery is powering only the coil and a rear single tailight.

Coil draws an average of 3A and the bulb about 1A.

So, I have used about 8Ahr from that battery.

I just checked the voltage of that battery, it READS 12.94V (averaged between three different volt meters).

Your "test" is not valid, you NEED to start with a FULLY charged battery. Then apply a known load, check and log voltages periodically during the test.

This establishes a BASELINE to work from.

Something else to consider, using a incadescent bulb as a "load" is not a good idea. The bulb current will not change in a linear fashion as the battery voltage drops and will mess with your results. Much better to use a RESISTER as a load, will still drop current as battery voltage decreases but gives a more predicable linear load to work with.

But personally, I DON'T bother with "testing" my batteries in such fashion. I don't stress over it and yet they give me a minimum of 9 yrs of trouble free service.. :B

Heck my last set could have gone MUCH longer, I only changed them out so I didn't have to worry about them not having enough life left while on the road..

But go ahead and do it "your way", it is YOUR "world" to play in..

[Lantley]

BFL13 wrote:
Just use the xx^&* hydrometer!!! Then we will know something useful, and we can help with the rest. Right now you don't have any proper meters and are just guessing, and confusing everyone.

I agree. The OP is doing all wrong and then asking for help, but only on his terms.
It's tough enough to diagnose or analyze a situation on line as it is.
Getting a mish mash of questionable data/facts causes the entire effort to be futile.

[2oldman]

wopachop wrote:
Use a water meter to measure how many amps i remove

Good one.

[wopachop]

I got to take some of the blame as it happens to me a lot on forums. I write big long confusing posts and some people dont absorb it correctly. It seems like time2roll followed along just fine. While others are yelling at me saying 12.64v is not fully charged. I was hoping we all agreed im closer to 90% charge from the 5a battery tender and the main question of the thread is should a 4a load make the batteries drop to 12.4v?

[MDKMDK]

Nice going wopachop, you've got the forum battery charger brain trust running in circles over this one. Great entertainment. Thanks. :B

[BFL13]

Just use the xx^&* hydrometer!!! Then we will know something useful, and we can help with the rest. Right now you don't have any proper meters and are just guessing, and confusing everyone.

[wopachop]

Im leary about taking SG readings too often. Have you heard the jokes about the guy who buys a brand new helmet but doesnt wear it because of fear to scratch it?

Thats like me with my brand new batteries. I dont want to remove a single drop of electrolyte from them. Which i know is going to happen every time i take a reading.

I do have a plan for later. Out of curiosity im going to manually fully charge the GC batteries. Use a water meter to measure how many amps i remove. Then for fun hook it up to the 5a battery tender and see how many go back in. Will record voltage of everything and plot on a graph.

I 100% agree the battery tender is not a good choice. Its just a quick temp choice for now. Might use the HF battery charger later today. I want to test both actually down the road.

[wopachop]

I used a watt meter to measure how many amps i pulled from the batteries. Also it was a standard 12v auto bulb that pulls around 0.9a and i left it on close to a full day.

[BFL13]

"My fancy German hydrometer called them 1.285-12.280 brand new from the store."

Ok, so that is right. You then pulled them down by 20AH, which is not much, so they should be doing better. So the question is - how did you measure that 20AH? Perhaps it was more than that?

The big question is what is the SG now? If not too bad, then we have to question the other numbers. Mostly, believe the hydrometer.

Another thing about voltage drop is where you measure it on some wires to a meter. Long and thin wires can give you a bigger drop than taken right from the battery posts.

[wopachop]

Gdetrailer wrote:

Get it?

Yes i get what youre saying above but it doesnt relate to this particular example. Thanks for trying to help though.

[Gdetrailer]

wopachop wrote:
We have the red HF charger here too. I trust the battery tender more to be honest. I wanted to leave it overnight. Instead of pumping in 10amps for a certain amount of time. I understand it has a "normal flooded" setting.

So i restarted the test. Batteries rested for 1 hour and were at 12.64v.
Plugged in 4amps and lights and at:
1. 10 mins 12.43v
2. 20 mins 12.42v
3. 30 mins 12.41

Not sure why i got 12.3v earlier.

So lets start over. Lets pretend we trust the voltage of my new batteries and theyre at around 90%. Is that normal to sag to 12.4v with a 4amp load?

NO.

Not "normal".

Not good.

12.64 is not FULLY CHARGED AT REST, should be right around 12.8V.

THEY ARE PARTIALLY DISCHARGED.

You are on the road to ruining them by allowing them to continue on at that state.

Throw that "maintainer" out, forget about it for THIS PURPOSE.

USE THE STUPID HF CHARGER FOR WHAT YOU ARE DOING.

That HF charger WILL NOT "PUMP" IN 10A for the entire time, it WILL TAPER as the voltage of the batteries rise and will do no harm (or much less harm than severely under charging which is what you are doing).

LEAVE IT ON FOR AT LEAST TWO DAYS TO ALLOW THE BATTERIES TO GET FULLY CHARGED.

Get it?

[time2roll]

For a pair of GC2 at 90% that could be normal. GC2 does sag a bit more under load than the 12v combo batteries.

Also a GC2 will take 10 to 25 cycles to reach full capacity. Although don't expect to gain much.