Variac For Equalizatiion Of Batteries

[MEXICOWANDERER]

Note this is a long post and you might want to cut and paste it to your word program so you can relax and take little bites at a time.


USING A VARIAC COUPLED TO A MANUAL BATTERY CHARGER TO EQUALIZE BATTERIES

NOTE: A manual charger is one that has a heavy transformer inside. A ten ampere charger should weigh a minimum of seven pounds, a 15-amp charger is the size of a hat box. Manual chargers larger than 15 amps constant charge rating are usually huge with a handle and wheels. Don't try to use a VARIAC variable transformer with a lightweight “smart” high-frequency charger or converter. If the charger does not have a transformer, forget using a VARIAC. High-frequency chargers work normally, but generating no change in voltage output until you dial back the incoming voltage below 70 volts then the “smart” charger may go up in smoke. If you have an “Automatic” transformer charger that does not have a switch setting that turns it into a manual charger then don't try using a VARIAC with it or severe damage may result. The VARIAC, again, can ONLY be used with a manual battery charger with a heavy transformer inside. Some manual chargers like the Harbor Freight® 6 and ten ampere chargers are selectable between “automatic or manual” Choose the manual (or START) switch setting. DO NOT USE THE CHARGER'S ENGINE START 50 AMP “BOOST” SETTING UNDER ANY CIRCUMSTANCE with a VARIAC! The charger's transformer winding may overheat.

The VARIAC's operation is not magic. It is merely a user adjustable transformer with an adjustment knob for raising or lowering voltage that comes out of the VARIAC. VARIAC transformers usually are “plug-and-play”: They have a cord that plugs into a wall socket and a wall-type plug in socket right in the transformer housing. There is also a convenient on-off switch, a fuse, and a voltage gauge that tells how many volts the VARIAC is producing. To use a VARIAC, set the dial at “120” plug it in, switch it on and Holy Cow, nothing much happens! The first thing you should learn is that the VOLTAGE DIAL really is an ASSUMPTION of voltage dial. A reference. Huh? Well the VARIAC does not REGULATE AC voltage, it merely reduces it, raises it or when set just right, does nothing at all to change the voltage. The 120 setting on the dial is a REFERENCE POINT. It's real meaning is ZERO “0 change in incoming versus outgoing voltage”. Bo boost, no buck. The maximum setting is usually 130 volts (some expensive units may go to 140 volts or higher). If you are mathematically inclined, think of a VARIAC transformer's 130 volt setting as a “13/12ths boost to whatever incoming voltage the VARIAC is dealing with. All VARIACS can throttle voltage back to “0” and this, the backing-off throttling ability, is what the real value of a VARIAC does for battery charger usability. The 13/12ths “boost” capability is merely icing on the cake.

Let's play around a bit with the VARIAC and the battery charger. Turn the VARIAC on-off-switch off, spin the VARIAC dial ans set it at 0 (which means it will allow no voltage to pass through to the battery charger), plug the VARIAC into a LIVE wall socket or generator, connect the battery charger battery leads to the CORRECT posts (positive and negative, set the charger to MANUAL or ENGINE START 10 AMPS then finally plug the battery charger to the VARIAC.

WALL SOCKET (OR GENERATOR) > VARIAC > BATTERY CHARGER > BATTERY

If your battery charger has an on-off switch click it on, and DOUBLE CHECK the other switches on the charger to make sure it's set for manual charging. Don't bother fiddling with the battery charger's settings other than making sure it is set for 10-amps, or 15 amps, or whatever TWELVE VOLTS, even though you have connected it to a six volt battery! It's OK to do this/

Flip the on-off switch on the VARIAC to “on”. “Tah-Dah!” Now go look at the gauge on the battery charger. Because you set the dial on the VARIAC to 0, the charger is playing possum. Just like it was switched off, The voltmeter on the VARIAC will read zero as well. Excellent.

Now go to the dial atop the VARIAC. Twist it up to “100”. Look at the voltage gauge on the VARIAC. It should read somewhere between 90 and 100 on shore power. Likewise your charger amperage will have risen. But the charger amperage will be LESS than if you had plugged the charger into a wall socket. The VARIAC is “throttling: the charger! Now twist the dial up even more to “120”. Normal voltage showing on the VARIAC AC voltage meter. Your battery charger will be charging “normally” now, just like you had plugged it directly into a wall socket.

The “correct” type of charger will keep raising or reducing charger amperage as you keep twisting the VARIAC dial back and forth. You now have a throttle for your charger, but remember this throttle is like pressing on the gas pedal of your rig with a brick. It is not regulated, no battery charging voltage control. It ain't cruise control. Left unattended, your battery voltage will eventually climb too high. You need to keep an eye on things and not forget this thing is connected and charging. Unless you connect a manual shut off timer to the plug in cord, you need to switch this thing on and off yourself. I use a wind-up kitchen alarm clock cooking timer. Don't sweat it; this isn't going to be like playing a video game pac-man or Doom. This is going to be a relaxed operation.

YEAH YEAH YEAH I know you want to know “What'll she do?”. By twisting the VARIAC dial from 120 toward 130, you'll INCREASE the amperage output of the charger. But this is sort of like overclocking the central processing unit of your computer. No, I take it back – this is a LOT like overclocking the CPU in your computer. It can be risky with some borderline quality chargers. Trying to squeeze 20 or more amps out of a 10 amp charger may trip the automatic reset circuit breaker inside the charger or it can blow a “diode”. If that isn't enough to raise the hackles on the back of your neck, “overclocking” the charger on a hot day can fry the windings in the transformer if the charger is left huffing and puffing too hard. If you want to “chance it” with something other than a Harbor Freight 10-amp charger at least direct the blast of a fan at the charger while you're over-amping it. Some chargers like the HF tolerate 25 amps output surprisingly well. Just don't suddenly get stupid and try messing with the “ENGINE START BOOST” setting on the charger. That'd be a surefire recipe for smoke and possibly fire. If you're not sure about the charger READ THE MANUFACTURER'S DIRECTIONS before you start messing with fire. Your GUIDING LIGHT in this fairyland of charger gymnastics is the AMPERAGE gauge on the charger. But guess what? There's another critical meter reading that has been omitted until NOW...

The so-called “Holy Grail” of flooded lead acid battery voltage limit during equalization, is 16.0 volts on a 12 volt battery and 8 volts on a 6-volt golf car or L-16 battery. Fine-tuning these voltages are determined by temperature of the battery acid. It is assumed here that you won't want to go outside and play with the batteries in a blizzard or heat wave. But the volt meter itself, the voltage meter that must be connected to the battery that's being played with MUST BE REASONABLY ACCURATE. A digital handheld multimeter is plenty accurate enough.

“Boing – Boing” 0 volts to 130 (?) volts. Twisting the VARIAC dial back and forth is fun. But mind that upper limit on voltage of the battery and don't get crazy overworking the charger!

The “recipe” for equalizing a flooded lead acid battery is to impress a constant “CURRENT” through the battery. This means selecting a specific AMPERAGE value then sticking with that specific amperage as best you can until one of two things happen: The battery acid specific gravity returns to fully charged density or 16.0 volts is reached. Whichever happens first. CONSTANT CURRENT is the key and constant-current is the “bane” of all manufacturers of so-called “Smart Chargers”. They would LOVE to have way to do the equalization correctly with CONSTANT CURRENT, but they can't because it would cost a large fortune to design and market such a charger – and the market is too small. Ask any battery design engineer if the razzle-dazzle algorithim pulse charge circus tent style of “smart” equalization is an intelligent choice versus using the 5% of ampere hour rating “BCI recommended method” and you'll get a smirk.

I've got news for folks who think an “automatic” equalization is a smart way to desulfate batteries. It isn't at all smart. Even the most sophisticated “smart” chargers on the market are damned lucky if they completely desulfate a battery in need of equalization. I've screwed around with some very expensive smart chargers that did not desulfate (equalize) a battery in ten hours. The manual way, the one we're dealing with here, did it in 2-1/2 hours. This is not such a big deal at home where you can keep pressing the “equalize” button until you have a callous on the end of your finger. Most “smart” chargers need the luck of a gypsy, the sun, moon , tide and stars aligned just right to equalize a battery with a single equalization cycle. When you're trying to do this with generator power, the wasted time and gasoline is a crying shame. Send a “smart” charger to the corner wearing a “Dunce” cap.

Selecting a CORRECT SPECIFIC AMPERAGE for equalization depends on the type of battery you have. You have got to find out the manufacturer's “20 HOUR AMP RATING” of the battery. Some common figures are 85 amp hours for a group 24, 105 amp hours for a group 27, 110 amp hours for a group 29, 220 amp hours for an 8-D and 220 amp hours for a SIX VOLT golf car battery. Three hundred some odd amp hours for an L-16 battery.

The correct equalization charge (amps) rate is FIVE PERCENT of the amp hour capacity of the battery. A little over 4 amperes for the group 24, 5 amperes for the 27 and 29, 11 amps for the 8-D and 11 amps for the golf car battery. And yes, 16 amperes for an L-16 !

Why am I not screaming at this point. Six Volts! 12 Volts! ?

Because here is where the VARIAC IS MAGIC !

Set the VARIAC DIAL AT ZERO. I wouldn't even bother with the voltage selection switch on the charger. Leave it set on 12 volts EVEN FOR THE 6 VOLT BATTERIES ! But be CERTAIN that VARIAC dial is adjusted to ZERO. Why not use the charger's 6-volt setting for a 6-volt battery? Because MORE TRANSFORMER WINDING WIRE is used for 12 volts, and that added copper is going to help keep the transformer cooler. Let the VARIAC do all the work.

Flip the on-off switch on the VARIAC. Then with care, caution and precision, slowly turn the dial on top of the VARIAC upward. Looking at the VARIAC dial is NOT important. Looking at the amperage meter on the charger IS IMPORTANT. Set the amperage to whatever amperage is correct for YOUR battery equalization.

Remember, the VARIAC is not a voltage regulator. As your battery gets “equalized” the amperage is going to drift downward as the battery voltage slowly goes up. As long as the voltage has not reached 8.0 volts for a 6-volt battery or 16-volts for a 12-volt battery, keep tweaking that VARIAC dial to maintain the correct charging amperage. It is not necessary to play mother hen with monitoring and adjusting. But I would start tweaking it if amperage droops to 4 from 5. Or a massive L-16 amperage has drooped 2-3 amperes from the correct setting. Usually three or 4 tweaks is plenty enough during an equalization cycle. By the way the use of a fan playing on the charger is mandatory with a battery as big as an L-16 and as the battery proceeds upwards from 7.5 volts I wouldn't get too excited about keeping the amperage exact. The heavy construction of a Harbor Freight transformer 10 amp charger is impressive. It's even more impressive if it has cool air blowing over it. Use a fan. Face the fan to blow on the side of the charger is best. That's where you'll find ventilation louvers.

Hidden in all this uproar about chargers, VARIAC this, and amperage that, is the fact you you trying to influence a chemical reaction inside a battery. That is the end-goal, the rest of this stuff is just chrome hood ornaments and techno-babble.

When the battery acid in all the cells has reached 1.275 OR 1.280 whatever it was when the battery was new and fully charged, stop. This is a “Whichever comes first” operation. If the voltage reaches 8.0 or 16.0 6 or 12 volts, that is endgame. Let the battery rest for a hour or so. Chemical reactions are slovenly sloth. Then take a reading with your precision hydrometer. An older or mistreated battery that has one or more cells than cannot reach full specific gravity density has it's lifespan time-clock ticking louder. If the cell gravity in subsequent usage seems to fall really fast even though you're sure you are recharging the battery fully, this is a sign that the battery grim reaper is lurking nearer than you'd wish.

OTHER USES FOR THE VARIAC

I use a 300 watt VARIAC. It's big enough to power the Harbor Freight charger and it only weighs seven pounds. So for all intents and purposes up to a limit of 300 watts the VARIAC is a wonderful light bulb dimmer for INCANDESCENT bulbs and DIMMABLE 120 volt LED and CFL light bulbs. Use your head in deciding whether a VARIAC might work. If one of those solid-state type voltage adapters is downstream from the VARIAC plug in socket, the VARIAC will not work. The light bulb itself to be dimmed must operate off of 120 volts AC, and it must say DIMMABLE.

The VARIAC may be extremely useful to some folks who have had chronic headaches trying to power some small hand tools with a small generator. I have an 800 watt something or other gizmo 2-cycle generator that simply hates to power my 260 watt Weller soldering gun. I connect the VARIAC to the generator, run the VARIAC dial up to 130 and what do you know, the soldering gun heats up ALMOST as fast as it does when connected to public power. Just keep in mind the VARIAC is like a sheep with regard to voltage regulation. There isn't any. It plays follow-the-leader behind incoming line voltage, be it shore power or generator power.

Using a VARIAC with an inverter generator is possible but precaution is needed. The load on the VARIAC must not even come close to the CONTINUOUS power rating of the generator. The reason is inverters, even pure sine wave inverters go a little nuts when they get near their maximum potential. The “pure sine wave” changes to “square wave” and coupling square wave power to a transformer is a bad idea. Keep the burden on the generator lower than it's maximum rating by at least ten percent. A thousand watt inverter generator powering a VARIAC set to maximum, powering a Harbor Freight 10-amp charger will be OK

If you are tussling with using a manual battery charger like the Harbor Freight 10-amp with a small non-inverter generator, then a VARIAC will help regain lost amperage. A friend has a 3,000 watt el-cheapo generator that will not power the HF charger to the potential it has when connected to shore power. 18 amps on shore power and 11 amps with the generator is quite a penalty when burning Chanél No 5 priced gasoline. Connecting my VARIAC to his system rendered a full 18 amperes charge rate. He now has a twin to my VARIAC stuffed into a side compartment. Before your daydreams carry you off into fantasy land, remember a VARIAC has a WATTAGE limit. The smaller units also are limited to around a maximum boost of 8% in voltage. The following link will take you to a Surplus Sales site that has 15% plug-in voltage boosters for A.C. The voltage boost is fixed and cannot be altered or adjusted.

Surpluscenter.com

Search the site search engine for TRANSFORMERS. There's only a few models so finding it is a snap. Nine dollars, and they are plug and play.


THE OBLIGATORY -CANNOT BE OMITTED- “CAVEAT”

We've been playing with transformers. The VARIAC is an adjustable transformer. The necessary battery charger is Zombie stupid, merely a transformer with rectifiers and the voltage booster transformer mentioned above is also primitive. No integrated circuits, not a hint of “intelligence” anywhere. The instant that transistors, integrated circuits, RAM, ROM, PROM, or any type of electronic control circuit is introduced into the picture, VARIACS should take a quick “Stage Left” out of the picture. A VARIAC can only be used within the capacity limits of it's ability and it can not REGULATE voltage. If shore power voltage goes up and down for some reason, the VARIAC (and all other “dumb” transformers) play “Monkey See Monkey Do” The voltage coming out of the VARIAC will “track” and follow incoming voltage like a shadow, be it up or down.

BUT...

The CONTROL that a VARIAC affords a transformer charger battery charger makes the most “expensive” so called smart-charger equalization mode a Marx Brothers farce. So-called smart chargers cannot hope to accomplish what a human being can with a VARIAC, battery charger, digital voltmeter and an accurate hydrometer. It's like comparing the abilities of a Cray 2 Computer to an Abacus operated by a solid-state chimpanzee.

And you've not seen ANYTHING yet. Wait until how you can use the VARIAC and a transformer charger the CORRECT WAY to condition an AGM battery and recover lost amp hour capacity! I just used a VARIAC and my multimeter to emergency charge a 3.8 volt lithium power screwdriver. With a TWELVE VOLT transformer-type plug-in power supply! Transformer type plug in power supplies for devices and appliances are getting fewer and harder to find. The fully regulated type of wall-charger is rapidly gaining favor and you cannot use a VARIAC with a lightweight “switching” type wall-charger. If the charger is really heavy it has a transformer.

I connected my voltmeter to the battery. 3.2 volts. I plugged the wall-charger into the VARIAC, turned the dial to zero, then plugged in the VARIAC. Watching the voltmeter closely, I rotated the VARIAC dial to 10. No change in the multimeter reading, then more dial. At around thirty four, the multimeter reading said the lithium battery voltage had risen to 3.3. Tweak time. I backed off the VARIAC dial just a smidge. I wanted 3.25 volts. The charge time turned out to be a little more than a hour. You bet your sweet bippy I kept a hawk's eye on that voltmeter reading as it crept up bit by bit. When it reached 4.0 volts, I clicked the VARIAC off. This information IS NOT here to encourage someone unfamiliar with batteries and charging to go running off into the wild-blue. Unless you KNOW FOR SURE how specific batteries should be charged, I would stay away from operations like the stunt I pulled with the lithium iron battery. I mention it here SOLELY to demonstrate the POTENTIAL of a VARIAC.

By the way “VARIAC” is a name, a cute contraction of the term “VARIable A.C.”

[MEXICOWANDERER]

wa8yxm wrote:
Easier to push the button on the Prosine, Or just let the PD-9280 sit in float mode for a few days.

With a generator?

There exists a large percentage of flooded lead acid batteries that LAUGH at the attempts of a smart charger to bring the specific gravity of all cells back to OEM density. I recently talked to an individual that has twelve L-16 batteries connected to a generator and he uses the inverter (worth three thousand dollars) to try and equalize the batteries. Fat chance. He told me he gave up after ELEVEN tries. Eleven equalization cycles in a row. The inverter is set to it's maximum setting for equalization. I loaned him both my HF charger and VARIAC. I got a text message on my cellular during the middle of the night. "I'm on battery 4, and the first three are now sitting on 1.275 all three cells. Before I could not get them above 1.260. Hello lobster dinner! My reward.

The 15% boost transformer from SURPLUSCENTER.COM is described to AUGMENT a too small a generator's inability to feed the VARIAC with 120 volts. For straight out battery CHARGING, and NOTHING ELSE, one of these booster transformer can help a generator to CORRECT (not over-boost) AC voltages so a charger acts more "normal" in it's amperage output. If you use your small battery charger at home and when the batteries are discharged it charges at 10 amps but when you are camping, the same charger only gives out 8 amps on a generator despite the fact you checked the generator and it has normal output voltage THEN the booster transformer (this is not concerning the VARIAC) can make the charger's output "normal". OK? Just like "at home".

The booster transformer is used to connect between the generator and VARIAC (to boost the variac) when "120" is dialed in on the VARIAC and you "detect" less than 120 volts on the OUTPUT of the VARIAC. The transformer is used to keep voltage HONEST going into the VARIAC.

DETECT! The charger puts out 10 amps at home. It puts out 2 or 3 amps LESS when used with the generator. You can bet your bippy that when you dial the VARIAC to 120 using the generator the charger is going to act wimpy as well. The booster charger is used to keep things honest. When I dial 120 into the VARIAC I would PREFER that charger output stays the same using shore power or generator power. Got it? I don't need to fight a small generator when trying to get 16 to 20 amps out of a Harbor Freight 10-amp charger. The VARIAC's 13/12 boost by itself CANNOT CORRECT ENOUGH for a small generator's distorted waveform. This is Sooooooo easy to check for: If your TRANSFORMER TYPE battery charger puts out a reasonably predictable amount of amperage at home but puts out LESS amperage with your generator then you can use the nine dollar surpluscenter.com booster transformer. This booster transformer is only to be used to CORRECT inadequate voltage, not to TURBOCHARGE already correct AC voltage.

99% of the worth of a VARIAC is to BUCK voltage for a transformer type charger. To throttle it back. If you do not understand clearly the relationship or meaning or significance of a small generator's clipped sine-wave voltage peaks, and how it degrades the performance of a battery charger then get a knowledgeable friend to help.

Fighting an equalization exercise using a charger and small generator is not fun. Fighting batteries that fail to respond to an INCORRECT equalization using a "smart" charger inverter or whatever is equally unfun. Battery distributors ADORE people who ASSUME pressing the equalize button ASSUMES the battery electrolyte reverts to full rated specific density. KA-CHING!

[greenrvgreen]

I'm sorry, all I see here is another opportunity for me to burn my trailer down. Count me as another satisfied Prosine owner, and what my Prosine can't fix, my Visa card can.

[mena661]

Except the PD doesn't do a proper equalize. None of the converters do. I either use my HF or my portable B&D1093 for that.

[wa8yxm]

Easier to push the button on the Prosine, Or just let the PD-9280 sit in float mode for a few days.

[ralphnjoann]

Thanks for taking the time to post all this information. It's something I want to try since I already have a HF 10 amp charger. I have a couple of questions. First, you talk extensively about a Variac and how to use it then you refer us to a website that sells a fixed output transformer that gives a 15 volt boost. Can this be used in place of the Variac? Second, your Variac is 300 watts. Would this item from Amazon be of sufficient wattage to work with the HF charger?

Variac

Note: The item description contains the following, "Input: 120 volt AC, Output: 0~130 volt AC, 3 Amp Slow Blow Fuse
Max VA: 300VA, 3 Amp. Max (surge), 1 year warranty
A rating of 300VA means that at 100volt, the unit can sustain at maximum 3amp. If at 120 volt the unit can sustain at 2.5amp
Note that most device have surge (when first turn on) much higher than operating amp rating.
E.g, motor with 3 amp rating may have over 5 amp surge, and you will need 5 amp variac."

Does this information have any bearing on this unit's suitability for the project?

[westend]

Overheating shouldn't be an issue, if using a charger that can deliver the amps needed without the variac. In Mex's example, he is using the HF charger that has a 10 amp charging circuit. If using the BCI formula of 5% current, that is almost smack on for two 6v GC2 batteries and within the capability of the charger.

I use a variable autotransformer regularly. They can be used for other things too. Here's one I cobbled from a 240 double gang, I cut the shaft and made two 120v variable transformers:

[mena661]

ScottG wrote:
Your going to over heat the charger by over driving it to force more current out of it than it is designed to deliver.

Not the Harbor Freight one's he's talking about. I've gotten 19A from mine without the Variac and nothing is overheating in the process. GREAT POST MEX!!!

[ScottG]

Your going to over heat the charger by over driving it to force more current out of it than it is designed to deliver.

[ken_white]

You have to be careful when you over-voltage any device, especially since a Variac contains no isolation. Just something to think about...