schumacher 55 amp smart charger question

[Tyronedeblanco]

According to the manual, i can put the......(schumacher 1555A   In automatic mode, the charger will stop when the battery is fully charged. After charging is complete, this unit will maintain the battery at  13.4 Volts to prevent self discharge. To activate the automatic feature, first connect the clips to the battery and select the desired charge rate. Then, press the ?symbol once and “Aut” will be shown on the display. When charging is complete, the battery % will show “100”.)

Do i need to set it to the 20A/2A trickle charge option for it to maintain the 100% charge?  Or do i just leave it on the 55A option while on auto?  is this safe to leave it like this?  Im a bit concerened leaving this on all the time for saftey reasons and am also wondering what kind of energy bill is this gonna run up. 

Charger is listed on amazon below.

http://www.amazon.com/gp/product/B006PAGJXQ/ref=as_li_ss_il?ie=UTF8&camp=1789&creative=390957&creativeASIN=B006PAGJXQ&linkCode=as2&tag=knowledgepubc-20

[FreeLancer]

I got one from Walmart on Harris' recommendation and have used it to charge a pair of golf cart batteries.  The automatic feature works on the 55, 20, and 2 amp settings, although the fans still run hard after it reaches maximum charge, so I'm not sure how much current they draw in trickle mode.  I disconnect mine from the Schumacher and put a Battery Minder on it to keep it maintained.

In the future I will only be using the 20 amp setting when charging less than 4 batteries because the 55 amp setting boiled off the water below the top of the plates in just a couple hours.  That pair of batteries is probably ruined, but I have not put a load on them since refilling and recharging.  This misadventure has me convinced to get AGM next time, in addition to no worries about spills, I don't have to worry about constantly checking water levels.

[kevo]

Perhaps you should call into the THINK line so Steven Harris can answer this as part of Expert Council.

[iam4liberty]

Do i need to set it to the 20A/2A trickle charge option for it to maintain the 100% charge?  Or do i just leave it on the 55A option while on auto?  is this safe to leave it like this?  Im a bit concerened leaving this on all the time for saftey reasons and am also wondering what kind of energy bill is this gonna run up. 

The Schumacher FAQ explains this better than their manuals.  Specifically see the section called "What is Maintain mode": http://www.batterychargers.com/Content.aspx?PageName=FAQS

Interestingly, Schumacher only recommends using their 1.5 amp charger for long term storage, see section "How long can I leave my charger connected to my battery?"

For the reason FreeLancer cited,  I would be very reluctant to use a 55 amp setting as the long term charge mode alternating with maintenance mode.  The 55A mode seems overkill for anything but quickly charging the battery bank, for example simultaneously charging it while  running a generator for a couple hours for a different reason.  Based on my experience with the 10 amp mode of the Schumacher XC10, I would imagine the 20A mode on your charger would be more than sufficient for routine charging without running the risk of the 55a rapid charge.

I also would love to hear Steven's take on this.

[Skunkeye]

A good rule of thumb for lead-acid batteries is to try to charge them at a rate no higher than 1/10th of their amp-hour rating.  So if you have a 250 Ah battery, you should charge it at 25 amps or lower to prevent heating.  You can charge at a faster rate occasionally, but you need to watch it very closely, so you don't reduce the lifespan of your batteries.

[Tyronedeblanco]

im gonna submit this question to Jack and maybe ill get his take on it or steven harris.   I was contemplating buying another smaller charger anyway, 2 is one, one is none.......but id like to know as well what i have / what is best.   

[bob3]

I'd be interested, too.  I bought a Schumacher XC103 30-amp and want to leave it connected in Maintain mode to two deep cycle marine batteries in an off-site storage room, but I don't want ANY risk of battery damage or worse because I will not be monitoring this, and if I do this, it will be plugged in for weeks at a time with no supervision.  I'm anxious to hear the feedback before I begin.

[FreeLancer]

A good rule of thumb for lead-acid batteries is to try to charge them at a rate no higher than 1/10th of their amp-hour rating.  So if you have a 250 Ah battery, you should charge it at 25 amps or lower to prevent heating.  You can charge at a faster rate occasionally, but you need to watch it very closely, so you don't reduce the lifespan of your batteries.

I believe my pair of GC-2s would be at least in the 450 Ah range.  I've been charging them at 5 amps (which takes days) and the water level never budged in a year, at 55 I lost over an inch in about 2 hours.  Live and learn, $180 down the drain.  Unless anyone has any tricks for reviving them.

[Tyronedeblanco]

well, until i get some clarification, im just gonna leave it close to 100 % and monitor every few days what the % is at. 

Also, i noticed some kind of smell when im charging with the schumacher.  It was both at 55A and 20A  i only ran the 55 A for a bit. 

I think my water level is ok, but im trying to find some pics online to verify a correct water level.  S. Harris's videos were hard to tell where the water level is supposed to be.

Freelancer, i dont know how to restore batteries.  Are the batteries still under warranty?  I just bought mine and they have a 1 year return policy, but im not sure if you can return them if the water goes dry.

[FreeLancer]

Also, i noticed some kind of smell when im charging with the schumacher.  It was both at 55A and 20A  i only ran the 55 A for a bit. 

I think my water level is ok, but im trying to find some pics online to verify a correct water level.  S. Harris's videos were hard to tell where the water level is supposed to be.

I got a sulfurous smell as well, you should probably check your water levels.

To check, just pop the caps off and make sure there is liquid covering the tops of the lead plates inside each cell.  If you see an inch of bare lead staring back at you, like I did, you're in trouble.  If you need to add water, only use distilled, not tap water.  I put nearly a gallon in mine.  Incredible, it boiled off a gallon of water in a couple hours.

Freelancer, i dont know how to restore batteries.  Are the batteries still under warranty?  I just bought mine and they have a 1 year return policy, but im not sure if you can return them if the water goes dry.

I might be able to deceive someone into taking them back at Costco.  But that's not right.  I'm the one who screwed up, it's my fault and I'll bear the cost. 

[Skunkeye]

Are the tops of the plates (where they were run dry) covered in crystalline deposits, or do they look more or less like the rest of the plates?  If the sulfation wasn't too extreme, and you refill and then charge them very slowly (1 or 2 amps), you might rescue them.  If the tops of the plates are completely covered in sulfur deposits, they're probably goners, but if the damage wasn't too severe, you might be able to bring them back with a long, slow charge, causing the sulfur to dissolve back into the electrolyte.

[FreeLancer]

I just sustained a 1000 watt load for 65 minutes out of the fried pair of GC2s before the 2300w inverter shut down due to low voltage.  With at least 400ah of capacity, it seems like I'm getting only a quarter or less of what I should expect.  But I might be missing something in my calculations.  I know I was able to get a lot more out of it before.

I'm going to slow charge them again over the next few days and see if they improve at all running the same load.

[iam4liberty]

I believe my pair of GC-2s would be at least in the 450 Ah range.

Hmmm...if memory serves, a pair of GC2s would be about 220 AH when in series at 12 volts.

I just sustained a 1000 watt load for 65 minutes out of the fried pair of GC2s before the 2300w inverter shut down due to low voltage.

That would be about 90 AH of discharge (actually probably closer to 100-110AH given inefficiencies).   So the battery would be 40-50% discharged.  At that discharge the rest voltage would be getting close to 12 volts.  With a heavy current draw this could drop it into the 11s triggering the inverter alarm.  Did you happen to measure the voltage of the battery at rest after the discharge?  Also, what is the cutoff voltage for your inverter?

Of course, my math could be off.  But if it is right, your batteries may not be in too bad of shape.

[FreeLancer]

Duh, you're right, two batteries in series doubles the voltage, while the capacity remains the same.

The inverter shuts off below 11v, which I believe corresponds to a deeper discharge than 50%. So, while better than my previous estimate, the capacity still seems a bit low.

[iam4liberty]

The inverter shuts off below 11v, which I believe corresponds to a deeper discharge than 50%. So, while better than my previous estimate, the capacity still seems a bit low.

Actually, I think it may be spot on.  There is something called Peukert's effect where the capacity of a battery declines based on the rate of discharge.  The 220ish amp-hour rating would be for a 20 hour discharge (i.e. ~10 amp) rate.  See "high energy discharge rates" here for more details: http://www.chargingchargers.com/tutorials/batteries.html 

There is a spreadsheet in the wikipedia article on Peukert's law which calculates the amp hour capacity at different draw rates:

http://www.smartgauge.co.uk/peukert_depth.html

If we enter 1.3 for the Peukert constant (common value for flooded cells) and 220 AH capacity @ 20 hour rate it generates a table showing discharge rate (in amps) and capacity.  For an 88 amp discharge rate the battery would have a capacity of 118 amp-hours and would last 1.34 hours total.

This is perfectly consistent with your story above.  You probably pulled ~100 amps out of the 118 amp hour capacity available at that discharge rate.  This would definitely shut off your inverter because the no-load voltage would be below 11 volts at that percent discharge.

If you tested it with a smaller load than 1000 watts (say 100 watts), I bet you would see a capacity much closer to 220 AH.

[FreeLancer]

+1 iam4liberty, you deserve some karma!

That helps a lot, and I'm kind of amazed that they are operating in the normal range after being cooked dry.  I'll check the links out this weekend, by then they should have finished a 5 amp slow charge and I can do another run at a lower rate of discharge.

Thanks for your help.