Old tech to the rescue

Battery chargers for every need

Allan Tarvid

August 26 at 2:25 pm  | Mobile Reader | Pring this storyPrint 

High-tech smart chargers are smaller, lighter and take better care of our batteries, but sometimes it takes a boost from an old-tech transformer charger to save the day.
High-tech smart chargers are smaller, lighter and take better care of our batteries, but sometimes it takes a boost from an old-tech transformer charger to save the day.
Allan Tarvid

My town doesn’t allow people to talk on a hand-held cell phone while driving, but hands-free talking is OK so I keep our phones paired through Bluetooth to our two vehicles.

Somehow my phone and my tow vehicle became unpaired, and I sat in the garage late one evening to put them back in touch with each other. I was actually doing three things at the same time, and I ended up distracted enough to leave the key in the truck with the ignition turned on.

I came out to the truck the next morning, and when I opened the driver’s door I noticed the truck’s courtesy lights didn’t come on.

Uh-oh.

Sure enough, the battery was stone-cold dead. I retrieved my keys and headed for the battery charger shelf.

I grabbed one of my favorite automatic smart chargers and hooked it up to the truck’s battery. I always make the battery connections first, and then plug the charger into the wall. I plugged it in and it wouldn’t charge the battery.

Rats! Was my battery done for?

My brain finally overrode my surprise: One of the first things a smart charger does is make sure that the charging leads are connected properly and not reversed.

The charger can’t “see” if you have the red clip attached to the “+” terminal and the black lead to the “-“ terminal; it has to sense the correct or incorrect polarity through its charging leads, and if the battery is absolutely dead there is nothing to sense.

Smart chargers also need to sense the amount of power left in a battery to properly regulate the charging output.

My intelligent charger couldn’t verify that it was properly connected and couldn’t read any remaining charge level in the battery, so it assumed something was wrong and wouldn’t release any charging current.

It was back to the charger storage shelf and more searching. I dug through the dusty units until I found an old bench charger built with transformer technology — a “dumb” charger if you will.

These old chargers use transformers to step down the voltage coming from your wall socket to a battery-charging level. A good wall socket offers 120 volts, and it needs to be reduced to 13.8 volts for charging.

The alternating current (AC) coming from the wall is not compatible with the direct current (DC) battery you are trying to charge, so these chargers also convert or “rectify” the AC to DC.

Well-built transformers are constructed to reduce our standard 120-volt, 60-cycle power to 13.8 volts without any extra regulation. That would be great if all wall sockets put out a perfect 120 volts. The output of a transformer is directly proportional to the input feeding it, and if you have lower voltage going in you get lower charging voltage coming out.

If your boat charger is plugged into an outlet at a marina that’s at the end of a service line (maybe also at the end of a long extension cord) you are probably going to have less than full AC power going into it and, therefore, less charging power coming out.

Some transformer-based chargers have transformers windings designed to put out a higher-than-ideal charging output that is then regulated with electronic circuits. These can help the charger compensate somewhat in at least some low-voltage situations.

Back to my garage ….

One of these transformer chargers will put out power to a dead battery, and my old relic saved the day for me. Mine is a 10-amp charger, and I left it connected to the truck’s battery long enough for the needle on its charging amp output gauge to drop down below the 10-amp mark.

One seemingly odd thing about these chargers is that they only put out their maximum-rated amp output when charging a completely dead battery. As the charge in the battery builds up, the amount of current coming from the charger is reduced. The meter on my charger started out reading about 12 amps, and I left it connected until it had built the battery up enough to reduce the reading to 9 amps.

Then I unplugged and disconnected the old charger and reconnected my smart charger. Happily, the battery now had enough stored power to convince the smart unit to begin normal charging.

I won’t connect one of the old transformer chargers, and then just walk away and forget about it because most of them don’t shut off automatically. Their output reduces as the battery’s stored charge increases, but their lowest output level is still too high to be safe.

Once a battery is fully charged, it needs only enough charging input to replace the normal self-discharge batteries experience during storage. Most transformer chargers act like unregulated trickle chargers and continue putting out more power than a fully charged battery needs. This can result in a damaging overcharge.

Some transformer chargers have built-in timers you can set to allow enough charging time to replenish the battery and then shut off. Then, you have to check the battery’s state of charge regularly and, each time it falls to 75 percent of a full charge, calculate the amount of charging time necessary to top it off. Transformer chargers without timers required you to be the timer.

All this bother, and the fact that most of these chargers were not water resistant enough to be mounted onboard a boat, spawned the invention of the 24/7 smart charger. These solid-state chargers are smaller and lighter because they don’t require the heavy and bulky transformers.

They also charge faster because they aren’t slowed down by the earlier technology’s “output power goes down as state of charge goes up” trait.

They charge batteries in three stages: a timed “bulk charge” that delivers full charging power to the battery right up to the regulating circuit’s set point (often 14.2 to 14.4 volts),a constant “absorption charge” held at a level that slowly tapers off but sustains the desired voltage (especially important to flooded-cell batteries because it maintains their gassing level long enough to knock sulfates off the plates to prevent sulfation and mix up the electrolyte to prevent stratification) and finally a “float charge” that maintains just the right amount of current to compensate for natural internal losses over time without overcharging the battery.

My favorite portable smart charger, PulseTech’s Xtreme Charge model (xtremechargers.com), also conditions the battery with pulse charging technology to prevent or break down sulfation.

You can’t beat the new breed of smart chargers for speed, efficiency, light weight and the promotion of longer battery life. But, don’t give away your old transformer-based bench charger — you never know when you might need old tech to come to your rescue.†

Transformer-based chargers often have dials allowing you to monitor charging.
 





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