Finally bought a battery hydrometer, need help with results

[RDMueller]

I have read repeatedly here how you need a hydrometer if you want to really know the SOC of a battery. This was clearly confirmed with the results I got...

Battery is a new, never used Interstate group 24 12v marine battery. I've had it for several months now and it's just been sitting in my garage on the Battery Tender. The date code shows it to be almost a year old though, so I'm sure it was somewhat discharged before I got it.

Anyway, I disconnected it from the tender and waited about 24 hours before testing. All 6 cells were pretty close to each other, but the SG was only 1.225 to 1.250. If I understand correctly, fully charged they should read 1.275. I don't understand why the battery wouldn't be fully charged since I had it connected to the tender. I can't imagine it would be sulfated since it's never been used, but what explains the low SG?

Hydrometer is a EZ Red 101.

[RDMueller]

MEXICOWANDERER wrote:
800 ma @ 18vdc OCV per 100 AH is my guideline. Transformer based wart.

I actually have an 800mA 18vdc wart. I guess it would be perfect for a group 27 battery, maybe a little big for a group 24, but I could try it next, maybe just not leave it too long.

[MEXICOWANDERER]

800 ma @ 18vdc OCV per 100 AH is my guideline. Transformer based wart.

[RDMueller]

Update: looks like I hit the ceiling with this wall wart. Another 36 hours later the charging voltage is unchanged at 14.25V and SG is still 1.250. I guess this 300mA wart just doesn't have enough power to get the voltage any higher, even though unloaded it is about 18v.

So, moved on to another wart I found. On this one the label says output is 12VDC and 1A. I measured the unloaded voltage at 16. Connected it to the battery and within a few minutes the voltage was steady at 14.7. Now we may be getting somewhere!

[westend]

RDMueller wrote:
Charging voltage this morning is up to 14.25V from 13.3 last night. This evening will be 48 hours and I'll take the SG then. Sounds though like something this small, only 300mA, will never get the voltage high enough to achieve a full charge. Still though, interesting to see what happens!

Stay with it up to your target voltage and run it for an hour or until you go .10 V above.

FWIW, last night I had a reason to make sure both my back up car jars were fully charged. Starting voltages were at 12.3 V and 12.6 V. As far as I know, these are identical model batteries but one is two years older. One battery was connected to a wheeled Exide shop charger and set at 2 amp output. The other battery was connected to the Wall wart at 500 ma rating. I unpowered both chargers this morning. The resting voltage now is 12.80 V on one and 12.81 on the other.

[RDMueller]

Charging voltage this morning is up to 14.25V from 13.3 last night. This evening will be 48 hours and I'll take the SG then. Sounds though like something this small, only 300mA, will never get the voltage high enough to achieve a full charge. Still though, interesting to see what happens!

[pianotuna]

From what I've been able to glean about charging rates, to equalize a battery one needs to provide enough amperage to get to the c/20 rate. That works out to 5 amps per 100 amp-hours of capacity.

[BFL13]

It's those darned watts. The low amp but high voltage charger can't get the batteries all the way up because it lacks the power to keep the amps going at the higher voltage.

I do know my manual trickle charger "stalls out" and can't get the battery any higher in voltage when it theory the voltage should just keep climbing till I shut off the charger. A bigger amp (more watts too) charger will get the battery higher before it stalls out.

[MEXICOWANDERER]

The warts are for storage. Buzzing a top charge every 4-6 weeks is still highly recommended. 5% amperage of total amp hour capacity until voltage reaches 15.0 then resume the wart. Wish somone out there was smart enough to realize this is the protocol flooded batteries scream for.

I like transformer based 15 volt warts. They are near indestructable for storage charge. If I am going to spend 65 dollars on a charger it is going to be a Megawatt. A sealed srorage charger might be worth the high bucks if it is used in the rain for a boat or ski doo. But for a single battery wintering in a basement seventy bucks is a bit rich for my blood.

[pianotuna]

RD welcome to the club. Battery charging is partly an art form and partly "dancing on the needles".

Charging lead acid cells is dependent on literally hundreds of variables. Not the least of these is that no two cells are ever created totally equal. It's as bad as snowflakes...i.e. possible to have 2 the same but really rather rare.

RDMueller wrote:
It's just when you get to batteries and charging in particular where there's a lot I still don't understand.

[RDMueller]

That clears up a lot! A Megawatt and and an ammeter is the plan. Also, the actual batteries I will dry camp with will be the T-105's. All this messing around with wall warts and the Interstate 24 really is more about education than anything else. I have a really good grasp of electrical in general, both AC and DC. It's just when you get to batteries and charging in particular where there's a lot I still don't understand.

[landyacht318]

500 mA, 0.5a might not be enough to get a battery to a high enough voltage that it can be fully charged with specific gravity maxed out . Many of these 0.5a wall warts simply cannot get a battery higher than 13.7 or 8, especially if it is a larger somewhat sulfated battery, and even when unloaded if the voltage is 18 volts.

AGM batteries tend to require less amperage to be held at higher voltages.
10 to 13% is a recommended charge rate, when one has all the time needed to complete the charge from a plug in charging source. When one is charging from a generator, then one does not want to run the generator for 9 hours just to meet this 10 to 13% recommendation.

One can indeed blast a battery with higher amperages. it is better to blast a battery with high amperage to a higher state of charge than it is for the battery to begin the next discharge cycle at a lesser state of charge and possibly fall below 50% because one was trying to slow charge it with the 'recommended' rate.

IF you get a Megawatt and an Ammeter, with your curiosity, you will accomplish so much more than the masses who want a plug and play automatic source to flash them a soothing green light and then add a year to their battery life in each praising of their green light purveying product.

I regularly hit my former 12v flooded battery with a 50% rate, and got close to 500 Cycles from it. Held to 10 to 13% rate maximum I would have come nowhere near that as there was not enough time to complete the charge before the next discharge began.

Amps and volts are not separate entities. Voltage is electrical pressure . Not enough pressure between source and battery and the amps can't flow . Once the battery reaches absorption voltage, the amps required to hold absorption voltage become less and less as the battery absorbs the top end of the charge. This takes about 4 hours once absorption voltage has been reached at the battery terminals, but the actual time varies according to many factors.

So get a real hydrometer and see how high the Specific gravity, and Voltage gets with your wall wart. It might not have enough juice to do the job, no matter how long it is left plugged in.

Or it might. You will have to tell us.

[RDMueller]

landyacht318 wrote:
OTC 4619

http://www.amazon.com/OTC-4619-Professional-Battery-Hydrometer/dp/B0050SFVHO

Leave charger on until all cells are 1.275 or higher.

If the wall wart/charger cannot get the cells to 1.275, you need a bigger charger.

After the cells are 1.275, then the maintenance charger should be able to hold them there.

Obsessing over voltage is common but unhealthy. Battery voltage when charging or discharging is like throwing a rock at a rubber band and trying to guess the weight of the rock by how far the rubber band stretched.

Most people cannot even hit the rubber band, much less see how far it stretched, but call their method gospel anyway.

That makes sense to me, but the thing I'm still having a hard time grasping is the relationship between volts and amps during charging. I get that, for example, if I had a charger that only put out 12.5V, it makes no difference how many amps it is capable of, it will never fully charge a battery. But, let's say you have a charger (a wall wart for example) that is capable of 15V but is only 500mA. It should fully charge the battery, it's just a matter of how long it takes. A 1A charger should do it in half the time, but either charger should be able to eventually get there because the voltage is high enough.

Also I get you should charge at 10-13% of the battery's C20. But I guess that's a max? Obviously you'll never get close to that with a wart and I guess that's ok? But what if you connect a 55A charger to a single group 24 battery? Are you going to damage the battery because you'll be charging at close to 70% of the C20?

It's funny, the more I learn, the more I realize I don't know!

[landyacht318]

OTC 4619

http://www.amazon.com/OTC-4619-Professional-Battery-Hydrometer/dp/B0050SFVHO

Leave charger on until all cells are 1.275 or higher.

If the wall wart/charger cannot get the cells to 1.275, you need a bigger charger.

After the cells are 1.275, then the maintenance charger should be able to hold them there.

Obsessing over voltage is common but unhealthy. Battery voltage when charging or discharging is like throwing a rock at a rubber band and trying to guess the weight of the rock by how far the rubber band stretched.

Most people cannot even hit the rubber band, much less see how far it stretched, but call their method gospel anyway.

[RDMueller]

MEXICOWANDERER wrote:
Anything from 13.4 - 13.7 finishing voltage is fine for a flooded battery up to around 100F. After that figure is broached reduce finishing voltage by .3 Oooooo lookie just the exact mount that a 5-amp Schottky diode provides.

:? But don't I need to get to 14.8? There's clearly something significant here that I'm still not understanding.

In the case of what I'm doing currently, the resting battery voltage was 12.3V. After connecting the fully charged jumpstarter to the Interstate and plugging in the wart, the voltage at the battery terminals rapidly rose to about 12.6 and stabilized. Over the course of the next 24 hours the charging voltage has gradually risen to 13.3V. I'm expecting that over the next several days it will continue to rise to the high 14 range as the battery approaches 100% soc. So where does the 13.4 to 13.7 finishing voltage come in?