Rebuilding old battery charger

[aja8888]

Looks spiffy--very Atomic Age. I'll bet it will soldier on for a few more decades.

Last winter, my neighbor borrowed it when he had a dead battery. In the summer here, batteries also die from too much heat, so it's a great tool to have around. I'll bet I'm the only guy on this block with a battery charger.

Someday, when the kids are "cleaning out the place", they will find this and probably won't know what it is for.

 

[aja8888]

... but has it been recalibrated to the NIST standard?

No recalibration necessary on that gauge. Plus, the transformer still looks good and I did clean the two spade terminals.

 

[NW-Bound]

Or rather, no adjustment has been provided. And the permanent magnet inside is probably all weakened with age.

Just joking. As long as the needle indicates some juice is flowing, the meter serves its purpose.


Hey, people, note the word "its" above, not "it's".

 

[samclem]

Last winter, my neighbor borrowed it when he had a dead battery. In the summer here, batteries also die from too much heat, so it's a great tool to have around. I'll bet I'm the only guy on this block with a battery charger.

A battery charger is one of those things no house should be without. Like a drain snake, a pry bar, duct tape, etc. Handier than a pocket on a shirt.

 

[NW-Bound]

I have installed fancy smart chargers in my RV. Yet, I do not have a stand-alone all-purpose charger.

I made one by putting a full-wave rectifier on the output of a 12V outdoor light transformer. I have a couple of these transformers left over when the lights that they powered deteriorated after a few years in the sunlight. For metering, I use a DC clamped-on ammeter. The charge current is puny (< 1 A) because the transformer output voltage is not right, but this home-made charger is enough to trickle charge batteries on cars that sit for a while.

 

[ERD50]

A battery charger is one of those things no house should be without. Like a drain snake, a pry bar, duct tape, etc. Handier than a pocket on a shirt.

Careful though. Nowadays, many (most?) chargers you buy are switching units, rather than a basic transformer/rectifier power supply. The new one I have won't output anything unless it detects some voltage from the battery it is connected to. Then it will dump a current into it, until the battery reaches a high limit of XX.XX volts (~ 13.8? I'd need to look it up). Then it shuts down until the battery drops to YY.YY volts ( ~ 12.8?). So it has a high duty cycle while the battery is low, and ends up just pulsing a short burst once in a while (minutes apart?) as it reaches full charge.

So it's pretty useless as a generic power source. But that's a good way to make a battery charger.

-ERD50

 

[ls99]

Speaking of old chargers, here is my beast.

 

[NW-Bound]

Even old chargers are not good as a DC power source anyway, because they are nothing more than a transformer with a full-wave rectifier. Hence, their output is full of hums, and does not have a steady DC component. They may burn out things that plug into cigarette plugs, such as phone chargers.

I have a desktop 13.8VDC supply which has a cigarette receptacle. Its output is regulated.

 

[aja8888]

Speaking of old chargers, here is my beast.

That's a fancy unit with 4 separate voltage settings. Very nice!

 

[ls99]

That's a fancy unit with 4 separate voltage settings. Very nice!

Yep, it can boil any size battery dry if not paying attention.

 

[NW-Bound]

Hence, the modern electronic ones.

I have two "smart" chargers in my RV. One feeds off the AC power, either off the grid or the genset, while the other one is a solar charger. The AC-powered one can pump 40A into the batteries, while the solar charger is a DC-DC converter that transforms the solar panel high-voltage output to match the batteries, while upping the current (a MPPT controller).

Both will function as a battery maintainer by trickle-charging them, when they sense that the batteries are full. Once every two weeks, they will up the voltage to more than 14V (do not remember exact value). The idea is to cause a bit of electrolyte bubbling to stir up the battery acid and prevent stratification.

By the way, the high-power charger is nice to minimize the genset's run time when I need to use it.

 

[aja8888]

Besides my antique charger, I also have a Battery Tender for maintaining batteries in storage for a period:

http://batterytender.com/

 

[ERD50]

Yep, it can boil any size battery dry if not paying attention.

The 8 volt setting is interesting, I don't recall seeing that before. Maybe some old radio batteries were 8 volt lead-acid?

Or was that a turbo-mode for a 6 V?

Even old chargers are not good as a DC power source anyway, because they are nothing more than a transformer with a full-wave rectifier. Hence, their output is full of hums, and does not have a steady DC component. They may burn out things that plug into cigarette plugs, such as phone chargers. ...

Right, they are only good for the crudest uses, or when you have a battery to smooth the output.

And there's a case where simple/cheap had some rather complex advantages. As the battery became more fully charged, a smaller and smaller percentage of that unfiltered waveform rose above the battery voltage, and the peak voltage delta became less. So this provided a form of pulse-width modulation and charge current modulation to reduce the charging current as the battery reached full charge, all done w/o any complex control circuitry at all. Today, that would be done with a 16 bit processor with megabytes of memory!

Of course you could still over charge a battery with those, the peak voltage would be high enough to account for tolerances and varying line voltage. But it helped.

-ERD50

 

[NW-Bound]

To cut down on charging time, my RV smart charger actually ups the voltage as needed to pump 40A into the batteries until they are full. Else, the charge current will taper off as the battery voltage rises, and it would take forever.

When I was flying electric RC planes with my son, we used "peak" chargers on our NiCad and NiMH batteries. These chargers also up the voltage as necessary to maintain a constant charge current. They sense that a NiCad battery is full when its voltage drops. This characteristic is not shared by the NiMH, whose voltage only stops rising.

I was amazed when seeing that veteran RC flyers drove their batteries hard, yet were able to use the same packs for a couple of years, and over a few hundred cycles. Upon further research, I learned that hard discharging in conjunction with "smart" charging was far healthier for NiCad batteries than what the typical consumer product did with these batteries, which caused the memory effect and often leakage.

 

[ls99]

The 8 volt setting is interesting, I don't recall seeing that before. Maybe some old radio batteries were 8 volt lead-acid?

Or was that a turbo-mode for a 6 V?




-ERD50

On the 8 volt setting it will float a 12V battery nicely at 13.3, measured long term. Long ago that was my only battery maintainer. It is a magnificent ripple charger.

 

[sailor]

The 8 volt setting is interesting, I don't recall seeing that before. Maybe some old radio batteries were 8 volt lead-acid?

Or was that a turbo-mode for a 6 V?

Some golf cart batteries are 8V (have 4 cells in series).

 

[NW-Bound]

One thing I should mention in case some novices happen to read this thread. Always charge a Lithium battery with the charger designed for it. Never ever try to jury-rig a charger to a Lithium battery (OK, you can, but you have to know what you are doing, and never leave it unattended).

Here's the reason. If overcharged, wet lead-acid batteries bubble and may spill acid. Sealed lead-acid, NiCad, and NiMH batteries may vent electrolyte through a safety vent. The above cause a mess and ruin the batteries, but are not lethal. Lithium batteries explode and catch on fire. They do not like to be overcharged at all, nor trickle-charged. When they are full, they are full. Absolutely no trickle charge.