Forum Discussion

Snowman9000's avatar
Snowman9000
Explorer
Aug 20, 2013

Desulfating with Harbor Freight charger

MEXICOWANDERER from an older thread wrote:
OK I'll pray I that I'll end up making this more confusing.

The charger has an "automatic" charging selection. It works on all but the 50 amp BOOST setting that obviously has to bypass a 25 amp circuit breaker. The boost setting should be used when the car won't start and time is money. For less than a minute anyway.

Secondly, I do not trust the automatic setting, period. With any battery any time, even when constantly monitored. It shuts off far too quickly (around 14 volts give or take a dozen).

To use the charger manually, to defeat the automatic @#$%^&!! setting, slide that switch over to "Start". Honorable Chinese decal maker not bi-lingual enough to understand that the word Start is a misnomer. The setting should say "Manual". For $29.99 you can't have everything.

The 50 amp boost only works on the manual (start) position. I could care less.

This charger just kicks the liverwurst out of an old Schumacher 10 amp, a Craftsman 10 amp, and "no decal" transformer style charger. The Harbor Freight transformer is WAY bigger and heavier. This thing just laughs as it is pumping out 18 amps into a discharged 12-volt battery.

It runs 10 to 20 degrees cooler under prolonged full load than other of my other transformer based chargers.

Some Chinese engineer got carried away when he designed this transformer. It reminds me of the $37.95 5,000 BTU window air conditioners we purchased 11 years ago. Goldstar. One set of 2 has been in operation for 11 years a half year at a time (5.5 years of operation at 100% loaded) and still perform like new.

Someone is going to eventually wise-up in China and figure out they don't need all that transformer. Then the charger will be like the rest of the 10-amp junk on the market. I intend to have a stock of $29.95 chargers by then.

**************************************************************

DESULFATION REGIMEN

Charge battery @ 14.7 volts or thereabouts until amperage decreases to less than 5% of rated amp hour capacity. Terminate charge

Apply CONSTANT CURRENT (as best you can, no less than 4% and no more than 7% of rated amp hours in amperes) Exp. 4-7 amps in a 100 amp hour battery.

Allow the battery to accept that CONSTANT AMPERAGE charge rate until one of four things happen:

1. All the cells revert to original specific gravity density (exp 1.275).

2. Voltage climbs to 16.0 volts (2.67 volts per cell)

3. Electrolyte temperature reaches 50C, 122.0F

4. Any cell boils violently, or emits smoke

Do not exceed the values above. Stop the charge if a value is reached, or of cell electrolyte goes nuts.


WEAR EYE PROTECTION! Hot sulfuric acid splashed in the eyes will cause instant total and permanent blindness!


I decided to try a desulfation with the HF charger today. The battery is a group 27, ~100AH. Its resting voltage was 12.62.

On the 10A Start setting, I immediately got 16.1v at 6.7A, with noticeable bubbling. Does that voltage mean there is nothing I can do? (see above)

On the 2A Start setting, I get 15.4v & 1.5A and extremely light bubbling. After 45 minutes or so, the volts were down to 15.2, and amps to 1.1. Still a small bubble per cell now and then. Is it worth continuing at this setting?

Before anyone asks, I do not currently have a hydrometer. It's broken, so I have to pick one up.
  • The NAPA store is getting my hydrometer in for me tomorrow.

    The battery is one year old, and the charged, resting voltage is down 0.1 from when it was new. I figured it wouldn't hurt to try the HF desulfation, to see if I can get back that 0.1 volt. Restore it to new condition, in other words.
  • A normal response after juicing it with 6.7 amperes!

    Equalizing means to make equal. All six cells. All returned to original equipment specification density. Let's call it 1.280 because that's what it probably is.

    IF THE BATTERY IS SULFATED yes it is worth continuing at this setting. You are probably asking yourself "How do I get that voltage to the baby bear ideal setting?" High is too high and low is slow.

    This is where that VARIAC I wrote about comes into play. Either set the charger on 12 volts "High" and tweak the VARIAC back to make the charger put out 3 amps or switch it to the 2 amp setting and spin the VARIAC dial up to make 3 amps.

    But you can equalize at the one point one amp setting. If the cells are badly sulfated it's going to take a couple of days to dissolve the hardened crystals back into solution.

    But without a hydrometer you are flying totally blind. Got a question for you if I may: What made you believe that the cell gravity did not return to OEM density after charging the battery normally?

About Technical Issues

Having RV issues? Connect with others who have been in your shoes.24,210 PostsLatest Activity: Mar 04, 2025