Temperature-compensated state-of-charge tables are available at batteryfaq.org. An IR thermometer makes it easy to check the temperature of a battery case (below the water line). I switched to the voltage method about 40 years ago, partly because I didn’t like messing with acid. (You can keep acid fumes off the terminals by using a cotton swab to apply an invisibly small amount of silicone grease to the seam where the plastic case meets the metal battery post.)
(I have come back to using a pointer hydrometer sometimes. It will show if there’s a bad cell. It can also detect stratification. Charging can cause water to rise. A battery won’t charge fully until the electrolyte mixes evenly. Sometimes in cold conditions, it won’t mix, and not getting a full charge occasionally, will shorten a battery’s life.)
Before checking a battery that has recently been on an alternator or charger, they say you should dissipate the surface charge by running the headlights ten seconds or letting the battery sit a few hours. In fact, it can take days. The colder a battery is, the longer it takes. An old battery may need days even at room temperature. I think “surface charge” is acid that hasn’t had time to permeate the electrolyte evenly after charging. Cold electrolyte is sluggish, and an old battery may have restricted pores.
The most common causes of battery failure are chronic undercharging (sulfate remains on plates long enough to harden), and chronic overcharging, ( plate material corrodes and flakes off). They’re bound to happen with DC charging. Manufacturers of alternators and chargers want a voltage that’s a happy medium.
I’d occasionally put an undercharged battery on a regulated charger overnight. Overall, it helped, but sometimes it made a battery worse. I can guess why. DC charging tends to produce bubbles. If a gas bubble blocks a pore in a plate, continued charging can seal the pore permanently. Also, in a low-maintenance battery, DC charging can cause calcium in a positive grid gradually to migrate to the lead oxide, grab oxygen, and form an insulating layer of calcium oxide.
Early in 2002, a neighbor discarded a 2-year-old battery that was out of warranty and would no longer start his car. Several months later, I used it to test an antique Sears charger I’d found. The charger restored it so well that I put it on my car. Every three months, I’d charge it overnight. That derelict battery gave me 11 years of reliable service.
An oscilloscope showed me that instead of DC, the charger produced 2-millisecond pulses. Charles Cady had invented it in 1959. He didn’t say it would restore a battery. He said it could continually charge a battery without damaging it. Nowadays, most smart chargers seem to use pulses. Battery chemistry can recover between pulses. Hydrogen and oxygen ions can better form water instead of bubbles. Metals like calcium tend less to migrate.
A scope showed that the Schumacher SC-1200A/CA was charging my car battery in bursts of 50 milliseconds approximately 500 milliseconds apart. The microprocessor probably changes the timing according to conditions. I know it changes the voltage. Sometimes it will charge at ~13.2 all the way to shutoff. Other times, it will switch to ~15.5 to top the battery off. It may start ~15.5.
When I topped off a battery that was at 98%, I watched the Schumacher apply 15.5 volts for half an hour. I had the filler caps off to watch the plates and electrolyte with a flashlight. With a DC charger, I would have expected to see bubbles sticking to the plates. I didn’t see any.
The Schumacher is easy to fetch because it’s light. It’s easy to position because it’s fairly small and has no exposed metal except the clamps. When turned on, the charger takes 20 seconds to show a percentage estimate. Then it applies a trickle charge for a minute before beginning to ramp up to a rate that seems to depend on what the microprocessor has detected about the battery.
I’ve read complaints that it may shut off too soon. Schumacher’s FAQ says it can happen with a cold battery. I tried it when my battery was at 25 F. It was at 77% charge, so it should have required at least 10 amp hours. In less than 1 amp hour, the charger said it was charged and shut off. The sluggish mixing of frigid electrolyte must have fooled the processor. (I think the sluggish electrolyte also affected my voltage check. Opening the door to release the hood latch would have pulled down the voltage a little, and it would have recovered slowly. It was probably about 82% charged.) In the cold, I could have used a manual charger, but there was no urgency, and maybe charging with sluggish electrolyte is a bad idea, anyway.
Even at mild temperatures, when I check voltage the next day, I may find that the charger shut off a little too soon. Maybe the acid needed more time to mix. No problem. When I get a chance, I let the charger top it off.
It’s the best lead-acid charger I’ve used, but I’ve found annoyances.
1. The 20-page manual is made of 5 sheets of 8.5 x 11” paper. It tells the user to read it before each use, but that’s asking a lot. It’s poorly organized and in two languages. With an extra sheet of paper, they could staple two 12-page manuals, English and Spanish, each with a table of contents and the important reminders visible at a glance.
2. The manual hasn’t been proofread. For example, Section 2 on page 2 says it’s only for 6-volt batteries of 24 AH and 12-volt batteries of 44-75 AH, and it’s only for starter batteries. That’s ridiculous. Page 6 contradicts these limitations, using batteries of 8 to 105 AH and 300 to 1000 CCA as examples.
3. Page 9 says if it fails within 2 years, Customer Service will give you an RMA. After several months, I noticed page 19, at the end of the Spanish section. It has two warranty-program-registration coupons, one in Spanish, and one in English. It says you should cut it out and mail it in within 30 days of purchase. It doesn’t actually say I’ve waived my warranty, but it implies it. I don’t like that.
4. The labels for the nine lights and two buttons are small like newspaper text. If the light isn’t good, I need to fetch reading glasses and maybe a flashlight. The display stays on only a minute. After that, if I want to check, I have to push a button. Accidentally pushing twice will shut the charger off.
5.The percent reading can say 75% when a battery is 97% charged or 34% when it’s completely discharged. The reading can rise impossibly fast or stay the same while a couple of amp hours go into the battery. The percent display is bound to be problematic. Schumacher’s FAQ says it shuts off by recognizing a charging curve, and it’s most accurate if left alone. There wouldn’t be much of a curve at the start.
6. There is no ammeter. I keep my Kill-a-watt P4400 (under $20) on the end of the power cord. The charger produces about 1 amp for every 20 watts input, so the watt meter serves as an ammeter. It also keeps track of how long the charger has been plugged in and how many amp hours have gone to the battery. The KWH display reads to 0.01. I ignore the decimal and divide by two: 0.08 KWH means 4 amp hours went into the battery.
7. The manual says it’s charged when the green light pulsates (growing dim every 8 seconds). The charger may display 100% and a green light long before that. After I became aware of the green light, I’ve seen it continue to charge at 4.5 amps for 25 minutes or 3 amps for 50 minutes, before it switched off and the light pulsated.
Another time, I watched the green light for two hours as the current tapered from 4 amps to 1 amp and finally shut off, and the light started to pulse. Since then, the battery’s impedance has been lower than before, so I think maybe desulfation took place. If a steady green light indicates “desulfation mode,” perhaps Schumacher doesn’t say it because some experts say there’s no such thing.
A processor may use “zero delta,” a point when charging voltage stops rising, to determine when charging is complete. Instead of desulfation, a steady green light might mean ambiguity, that charging is complete according to the computed curve, but zero delta has not been detected. A third possibility is that a steady green means both. The SC-1200A-CA designers may have found that if the processor doesn’t see zero delta, that means optional extra charging is in order, to clear up old sulfate.
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A car had sat in a neighbor's yard two months. She said the battery had been run down trying to start it after running out of gas. I thought maybe air had to be purged through the injectors. The battery would only click the solenoid, although my meter and my charger both said it was 50% charged. At one time, I would have thought a battery that sulfated should be junked.
After charging, the battery gave me a lot of rapid cranking (resting about half the time). When it slowed slightly, I recharged it. The second time, it performed significantly longer than the first.
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I've read that the SC-1200A-CA wouldn't charge a battery if the voltage had fallen too low. A neighbor's car battery was down to 0.8 V. I thought I’d have to start out with a dumb charger, but the SC-1200A/CA had no trouble. If sometimes this model hasn’t worked on a low battery, maybe the temperature of the battery was a factor.
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A neighbor has an antique that may require extensive cranking because it may sit for months and the choke doesn’t work. He’d sometimes leave his manual charger on the battery for days. One day when it sounded very week, I let my Schumacher put 48 AH into it. The next day, I found that the voltage had hardly risen, and now it wouldn’t turn the engine.
Strangely, after it sat on the ground several weeks, the Schumacher charged it quickly. The engine needed a lot of cranking the next day. The battery provided an outstanding 11 cranking volts, and it didn’t slow at all. Another rejuvenation!
Apparently, four years of overcharging with DC had caused calcium oxide to build up until the plates could not be charged. My first attempt to charge must have broken down the calcium oxide, but the freed calcium needed time to migrate back into the grid alloy.
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My two-year battery was three years old when I bought the SC-1200-A/CA. The battery charged at 3 amps, which was slower than similar batteries, and it supplied less voltage to headlights. After a year, I tried something new. Before topping it off with the charger, I used the parking lights to draw it down about 20%. Since then, it has charged at 4.5 amps and supplied more voltage to headlights. I guess 1-second bursts of cranking aren’t enough exercise to keep a starter battery in shape.
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A neighbor was about to replace a pair of 35 AH AGM wheelchair batteries because they were good for only 20 minutes of intermittent use. The wheelchair used an automatic DC charger. I put a 6 amp load on each of them for two hours, then charged with my SC-1200A/CA. His chair was faster than before, and he he said it would go all day on a charge.
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I’d owned the charger 10 months when it quit working. The display said it was charging, but the watt meter showed that it had shut off after a minute. I tried three times with two batteries. It had worked the day before, but two days before, there had been a drizzling shower while I was charging in the carport. The case hadn’t gotten wet, but maybe the cooling fan had drawn in moisture. I put the charger in a warm, dry place (115 F) for three hours. When I plugged it in, it worked again.
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I'd had the charger two years when I went to top off my car battery. According to the state of charge, it needed more than 10 amp hours, but after 2 amp hours, the charger switched to a pulsing green light and said it was fully charged. A test instrument found that I had more than a milliohm of resistance at the connections between the battery posts and terminals. I clipped the charger directly to the battery posts, and it gave the battery another 11 amp hours. I guess a tiny bit of resistance can fool the charger's processor, and it works most reliably when clipped directly to the battery posts.
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When my two-year battery was five years old, it began self-discharging at 5% per day, dropping by 1/3 in a week and 1/2 in ten days. The alternator was working normally and the parasitic drain was only 10ma.
I’d always thought that a car battery that wouldn’t hold a charge had to be replaced. With nothing to lose, I turned on the lights to draw it down about 20%, then charged with the SC-1200-A/CA. That was six months ago. It has been fine ever since. Dendrites can grow like cobwebs in a battery, forming paths for self-discharge. It looks as if the smart charger cleaned up the dendrites.
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I'd owned it 3-1/2 years when I again encountered the problem where the amber light said it was charging but the watt meter said it wasn't. Twenty minutes in a warm oven got it working. I got it apart by removing four screws. Two were under the lower corners of the display panel sticker. Inside I found a bit of leaf, showing that the fan can draw in debris. In one of the intakes was silk thread as if a bug had begun spinning a cocoon. The processor was soldered to a board on the display panel. The leads had no protection to keep dirt and dampness between leads from causing trouble.
I cleaned it with contact cleaner and a brush. One of these days, I'll take it apart again and spray on a conformal coating. This is a sensitive circuit that's bound to get dirt and humidity from the cooling air. I'm disappointed that Schumacher didn't apply a protective coating.
| Manufacturer | Schumacher |
|---|---|
| Brand | Schumacher |
| Model | SC1280 |
| Item Weight | 2.99 pounds |
| Product Dimensions | 9.96 x 4.29 x 10.03 inches |
| Country of Origin | Mexico |
| Item model number | SC1280 |
| Exterior | Machined |
| Manufacturer Part Number | SC1280 |
