ophirw

Hi,

I want to charge a Lead acid 12V battery with the 989 charger, I have read on the subject a bit on the net but have some questions not answered yet.

the battery is a 12V 9.5AH SLA (sealed Lead Acid).

what would be the ideal settings for the autocycle mode?
number of cells = 2 (from what I read in the forum each cell on the 989 is 6V)
maH = 9500 (the battery capacity)
Charge Amp = ?
Discharge Amp = ?
Cut Off volt = ?
Cut Off Temp = ?

will autocycling a lead acid battery revive it?
what are the C limits of Charging/Discharging a Lead Acid battery?

any other important tips i need to know but did not ask for?

thanks for the help :-)

ophirw

I got the follwing answer from MRC Support:

"You do not discharge lead acid batteries. Set the 989 to 2 cells, 9500 mAh, and 1.9 amps. That comes from multiplying 9.5 by 0.2. You can leave the temperature cut off at the default setting because charging that big of a battery at 1.9 amps will never cause it to heat up that much."

Bruce R B.

Hi,

     Just came across this post and found it very confusing.  The voltage generated by an SLA battery ( or any other lead-acid battery ) is , in theory 2.14 volts per cell.  We normally call it 2 volts per cell.  If you have a 12 volt battery then it must have 6 cells and you must set your charger accordingly.  The normal charge rate is set to C/4, or 2.375 Amps in this case.  You could use 2.3 or 2.4 Amps in this case.  Some newer batteries allow a faster charge rate than C/4 but you need to check the specs for this battery.

     I looked at the owners manual for the 989 and I must admit I have never seen such a poorly written manual in my life.  It tells you absolutely nothing!  I did notice that it mentions using a trickle charge on lithium batteries, which is an absolute no-no.  What they appear to be saying is that they use a CC/CV ( constant current / constant voltage ) regiem, which it the same as is used to charge a lead-acid battery.  The only difference is at the end of the lead-acid charge cycle you drop the voltage to a 2.3 volt per cell trickle charge, and with a lithium you stop the charging altogether so you don't destroy the battery.  I'm assuming that what they are refering to is the CV portion of the normal lithium charging cycle.

Bruce

Bok

I was able to successfully charge my car's battery with the 989 My mom borrowed my other car and left the dome lights on when she returned it. After 2 days, it wouldn't start anymore (key fob wouldn't even work), so I hooked it up to my 989. Set it to 2 cells, 2 amps, lead acid, and since it is a 106 RC (reserve capacity in minutes) battery, i set it to the maximum 19,990mah and left it charging overnight. When I checked the battery this morning it was done, and the voltage was about 12.6 volts, indicating a full battery. Set the 989 to charge at 1 amp and pressed start. A few minutes later it got to about 14.4 volts, and switched to trickle and varied the amps from .60 to 1.0 to maintain the 14.4 volts.

After that I put the battery back in my car and turned the key. Started in one click

ophirw

Bruce R B. - Thanks for the explanation. As for the fact that each cell is about 2V you are correct, that is exactly what confused me. I wanted to charge the battery but there was no 6 cell option only 5. So I looked for instruction but found none. I think that they call each cell 6V because the LA batteries come in multiplies of 6 (6V, 12V ...) & not as a representative of the actual number of cells.

As for charging a car battery a few months ago my brother in law came & his truck battery emptied, I wanted to charge it but the capacity of the battery was 130,000 mah. The 989 battery capacity doesn't go as high so I was afraid to use the charger in order not to cook it.

Bok

^ You can just restart the charging process after it stops. My 989 never got past 110 degrees Fahrenheit during the whole charging process, with an ambient temperature of about 87 degrees. Charging at 2 amps isn't that hard on the charger and power supply.

Bruce R B.

Hello again:

     Just came across the latest post and thought I'd try to clarify further.  You can charge your brother-in-law's truck battery with this charger but it will take many hours.  Although the charge rate for this battery would normally be 32.5 Amps (C/4, where C is the Amp/Hr battery capacity, normal rate for a lead-acid battery) you can charge it at a lower rate for a longer period of time.  This applies to any battery; there is a maximum charge rate for any given battery chemistry but no minimum.

     The charger manual would lead one to believe you could charge this battery at 10 Amps, but in the advertising a 120 VA (Volts X Amps) limit is quoted when the unit is used as a power supply.  This means that the built-in power supply can only supply 120 VA to the charger circuitry.  If you calculate back from the 14.4 volt charging voltage (the maximum voltage reached when charging a 12 V lead-acid battery), 120 VA results in a maximum 8.33 Amp current.  Consequently you could safely charge that battery at 8 Amps.  Since this is 1/4 of the maximum charge rate the charge will take four times longer than normal.  It could take a day or longer to charge this battery.  At a fully charged state the charger should read a voltage of 14.4 and a charging current of less than 8 Amps.

     Two other items of note.  If the voltage of the dead battery is less than 10.8 volts the battery has probably been damaged and may not take a full charge.  If the volage is considerably less than 10.8 volts the battery is definitely damaged and will not take a full charge; in fact it may not accept any charge.

     Secondly, the specs for your charger indicate it can be used as a power supply (as mentioned previously) with a maximum votage of 30  V and a maximum current of 10 A.  It should read 30 V or 10 A, whichever comes first.  At 30 V your maximum current is 4 Amps, and at a current of 10 A your maximum voltage is 12 Volts.  Anything in between follows a straight line between those two points.

     Finally, you charger should have built-in protection against any misuse (except gettig wet).  These include improper settings (the battery may be damaged but the charger shouldn't be), short circuits, reversed polarity (battery connected backwards), and overheating.

Best of luck, Bruce

ophirw

Thanks Bruce, that was the best explanation I got.

cracker

So if I have two 12v7ah sla batteries in parallel would my Mah value be 14000 and my cell count go to 4 or should the cell count stay at 2 and use 1.4 a as my charge voltage?
Thanks in advance.

ophirw

From my little knowledge of electricity when a battery is connected in parallel the voltage doesn't change, in this case stays 12V but the current doubles. When connected in a line the voltage doubles (24V) & the current stays the same.
My guess is that you will need to charge at normal voltage (12V) which means 2 cells but will need to increase the current (see Bruce explanation). since the charger has a limit of VA it will probably take double the time to charge. I think it is just like a 12V battery with double the capacity.

As a rule it is better to charge batteries separately if possible. only if the pack disassembles easily, since the charger monitors the whole pack but has no control over the current & voltage of an individual cell. charging them separately will make sure they will both be charged to the maximum. It will not take longer you will only have to swap the batteries when the 1st one is finished (charging each battery will take half the time of charging them together as a pack).

In any case I would recommend hearing another opinion just to be sure.

bekk

I used the above formula supposedly from MRC support (Set the 989 to 2 cells, 9500 mAh, and 1.9 amps. ) to charge an NIB torqmaster battery but adjusted for the 7.5 Ah rating on the battery. The charger began to indicated the battery was fully charged in less than an hour. I left it trickle charging overnight just to cover my bases. Is this the expected behavior?

ophirw

was the battery capacity 9,500 mah & you charged it with 7.5Ah? if this is correct than it should take about an hour & a half to charge.
by the way I think the battery comes charged, a LA battery shouldn't be empty.

bekk

The salesman at my LHS said the initial charge should be for 8 to 10 hours; so do the instructions on the side of the box. This was my concern since it did not take anywhere near 8 hours. The original post by ophirw stated that his battery was 9.5 AH, mine is 7.5; so I adjusted the number to 7500mAh at the same amperage. Took about 90 minutes to signal a full charge.

ophirw

The only thing I can think about is that the battery came charged or they said to charge it for 8 hours with the charger that probably comes with it that charges at around 0.9A.
the idea is to charge at a current that is about 20-25% of the capacity of the battery, in your case 1.5-1.875A. in this case it should take 4 to 5 hours to charge. this is only when the battery is completely empty, if its not empty it will take less time. this is why it is better to use a smart charger. if the battery is only half full it should take 2-2.5 hours to charge & so on.
don't forget to set the trickle charge, I set it at a current less than 10% of the capacity.
If you set it correctly I would trust the charger.

you can fully drain the battery & see how long it takes to fully charge it, but remember it is not recommended to leave a LAB uncharged.

just so you know, in all places the capacity of the battery = C.
so when you see C/4 it means 25% of the battery capacity.