Harbor Freight battery float charger #42292 circuit?

"P E Schoen" wrote in message news:o0vhkp$le0$ snipped-for-privacy@dont-email.me...

I have one of the cheap ($5) Harbor Freight lead-acid battery float chargers and I found that it was not working (it may have been damaged some time ago - I had the case open). I traced the circuit and it is basically a FWB and capacitor providing 25 VDC to a 7805 regulator with resistors to set the output to about 13.5 volts. But it also has a TIP41 NPN BJT with a diode and LED to the base, with the collector of a S9013 NPN and some resistors that appear to be intended to stop charging or perhaps inhibit charging if the battery voltage is too low. The schematics of various versions, and some modifications, are in the following:

The 7805 was blown in my unit so I replaced it with a 78M05 and I added a trimpot to adjust output to 13.5V. I also added a diode in series with the output to avoid damage from reversal. And I also removed R4 which essentially eliminates the function of the TIP41. It looks like the S9013 transistor is biased so that it will turn on when the voltage from the negative output lead to circuit ground exceeds 4.9V, and that will turn off the base drive to the TIP41 and turn off the output and the indicator LED.

It seems to work OK now and it is holding a charge of 13.23V on a 12 A-h SLA I charged overnight at about 0.33A. The battery read 13.13V when disconnected and a minute later dropped to 13.00. When reconnected it charged at 0.25A and after a minute dropped to 0.15A.

I had planned to build a high-tech charger/monitor using a PIC, and I still may do so, but for now I just want something that works. I might tweak the voltage down to about 13.2V which should be plenty to maintain charge on a FLA 100 A-h deep cycle battery I have, as well as the starting battery of my seldom used truck.

I also have a gel-cell SLA charger that I need to test.

Any ideas about that odd circuit with the TIP41?

Thanks,

Paul ===============================================================

I don't start my pickup for days at a time and the batteries were getting a bit weak last winter so I bought a little solar cell charger. Don't know if it helped or not, but the batteries made it through winter and then died in the summer (got 5 years from 6 year warranty batteries so no complaints). Found out warranties are much shorter now and prices have doubled, sigh. Anyway, I was a bit concerned about overcharging and needed a toy so I bought one of these to play with:

It is a "MPPT Solar Panel Controller Battery Charging Board 1-100W 5A 9V 12V

18V 24V Solar Energy Renewable" populated board, no case or leads. I had fantasies that it would be a buck boost circuit so would charge a 12 V battery even when the solar panel output was less than 12 V, but no, it is only a buck. What did I expect for $11, anyway :-). The solar panel is "ALLPOWERS 18V 7.5W Portable Solar Car Boat Power Sunpower Solar Panel Battery Charger Maintainer for Automobile Motorcycle Tractor Boat Batteries", just because that was the cheapest I found at the time. From my research it seems that with 15W or less panels and a car sized battery a controller isn't needed as you shouldn't be able to overcharge the battery anyway. I wanted to play so I got the controller. The solar panel has a cigarette lighter adapter to connect to the vehicle, with a little LED that has always bugged me since it draws current when the sun is down. Only 5 mA but I cut it out anyway. There is a Schottky diode in the panel to prevent battery discharge when the sun is down, so that is nice even without an external controller. There is an LED on the controller that only draws from the solar panel, and I verified that it draws no current from the battery when the sun is down. My dinky panel topped out at about 300 mA the day I was making measurements so the 5A rating is way overkill but it was about the smallest and cheapest I found. There is a pot for output voltage adjust, it comes preset for 13.5 V according to my meter, so I left that alone. There is a second pot for MPPT adjust, but absolutely no documentation came with it so I have no idea what this does. I emailed the vendor and asked for any info and they sent a hand drawn figure showing the input and output pins, just like on the board itself, but no other info, sigh. Anyway, it's double the cost of the Harbor Freight units but you don't have to rebuild it and you couldn't build it for twice that to use as a general power supply or a solar charger controller, but you do have to provide your own enclosure. I tried to play a little checking the output current and voltage and solar panel voltage while moving it around, and it did seem to change the panel voltage with load but I won't swear it was really MPPT. Just a long winded suggestion if you want to explore more options than your Yuasa.

----- Regards, Carl Ijames

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The TIP41 and S9013 form a comparator with positive feedback. No need for a dding your series diode as the TIP41 and its base 1N4007 prevent any revers e currents from the battery. If the battery has a shorted cell or is otherw ise damagingly low, the TIP41 should come out of saturation allowing the S9

013 to turn on and start diverting TIP41 base current etc until TIP41 is co mpletely off and S9013 is saturated on. But that's a real rough HFE depende nt threshold.

On that note, are there any good, reasonably-cheap SMPS 12V (14.4v?) battery chargers?

You would think that in this era of energy efficiency, linear voltage regulators + 50/60Hz transformers would be frowned upon...

Thanks!

Michael

[snip]

That solar approach is appealing. I have a pick-em-up truck that gets driven maybe once a month (bought new, 15 years old with only 39,000 miles ;-).

It would be troublesome to plug it in to mains between trips, but the solar, particularly here in AZ, should work great. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| STV, Queen Creek, AZ 85142    Skype: skypeanalog |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 

             I'm looking for work... see my website.

If you can get by with modest charge rates, there are "high efficiency" members of the Deltran Battery Tender family. The biggest of these seems to be the 5-ampere model.

I did a simulation and it seems to work OK according to the schematic shown in the first of the links above in the OP, but R5 is actually 400 ohms and not 400k. It also seems to be protected against reverse connection as you describe. Here is the simulation with steps of battery voltage from 8 volts to 16 volts 1/2 volt per step, then zero volts (short) and -12V (reversed battery).

And the ASC file:

Thanks,

Paul

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I thought that 400k looked funny, sets the S9013 threshold at about 7x 0.6 =4.2V. It also has a sneak circuit upon power loss with the battery disch arging around R5-LED+diode-BC junction of TIP41, which looks substantial- a lso maybe some discharge thru the 7805 bias network through base to collect or of TIP41 in inverse mode conduction... not even going to get into revers e battery mode.The circuit is basically trash. It's probably not even good for parts salvage since they're probably already salvaged from 30 year old junk they removed from boards with a torch and then washed them off in the yellow river. Harbor Freight, Northern Tools and all those Dollar this and that stores need to be banned from doing business in U.S.- they're merely a testimony to the stupidity of Americans- as if electing Trump wasn't enoug h of a clue.

Change the 7805 to an LM317 and adjust resistors accordingly.

The TIP41 circuit is weird.

Or simply toss most of it and change LM317 circuitry to a current source arrangement... documented all over the web. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| STV, Queen Creek, AZ 85142    Skype: skypeanalog |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 

             I'm looking for work... see my website.

If you want to do it right, locate the "charge-monitor" adjacent to the battery under the hood and follow a proper TC...

...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| STV, Queen Creek, AZ 85142    Skype: skypeanalog |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 

             I'm looking for work... see my website.

those voltage might be OK for a few hours a day in a car alternator.... but they are rather high for a 24/7 float charger.

m

The regulator in my 1989 Toyota truck probably is not very sophisticated, and does not really apply to a float charger needed only because I often don't drive it for weeks (even months) at a time. It is now charging with an old Schauer 6-8 amp charger somebody gave me about 40 years ago - still works fine - and stupid simple.

Here is some useful information if I decide to make my own high-tech battery charger, using a PIC:

Thanks for the information and discussion.

Paul

Wrong! They are the desired cell voltages at those temperatures.

My patents:

3,496,447 Alternator Voltage Regulator Responsive to Temperature 3,505,590 Temperature Responsive Output Voltage Apparatus 3,522,482 Temperature Compensated Voltage Regulation 3,546,563 Alternator Voltage Regulation Utilizing A Constant Current Source

By the late '60's _every_ (*) American car manufacturer was using one of my alternator regulator designs.

Ford, Chrysler, GM, and American Motors (Nash, etc, for you youngsters ;-)

I can't remember if Kaiser-Frazer was still existent, they aren't on my list.

A conventional battery charger will overcharge a battery if left on indefinitely, because it provides a voltage well above cell voltage. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| STV, Queen Creek, AZ 85142    Skype: skypeanalog |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 

             I'm looking for work... see my website.

From the second graph, the ideal voltages seem to be:

Temp Vpc V12 Tempco

0C 2.49 14.95V 25C 2.47 14.80V -6 mV/C 50C 2.38 14.30V -20 mV/C 75C 2.32 13.90V -16 mV/C 100C 2.25 13.50V -16 mV/C

The information I found elsewhere was about as follows, for state-of-charge after settling 3 hours:

SOC Vpc V12

100% 2.116 12.700 90% 2.083 12.500 80% 2.070 12.420 70% 2.053 12.320 60% 2.033 12.200 50% 2.010 12.060 40% 1.983 11.900 30% 1.958 11.750 20% 1.930 11.580 10% 1.890 11.340 0% 1.750 10.500

And my charging algorithm as originally conceived:

Initial charge at 0.2C for 5 hour nominal charge time for a 12 V, 12 A-h SLA initial charge at 2.4A Maintain charging until voltage reaches 2.4-2.5 Vpc = 14.4-15 VDC At 14.4V battery is 70-80% charged Keep at 14.4 volt until current = 0.02C (240 mA for 12 Ah) Float charge at 12.8-13.2V (or initiate new charging cycle at 12.5 volts (90%) Voltages are based on 25C. Voltage changes by -0.003 Vpc/DegC. So 14.31V at

30C and 14.49V at 20C

My battery is being charged at 13.85 volts at about 45C ambient (about 7C). That seems to be well below even the minimum of your charts (as well as I could read them). And my SLA is reading 13.42 volts. So those seem to be safe values. I find it hard to believe the "Ford limits" of 14.5 to 15.3 volts at about 20C. Even for fast charging (30+ amps) I would expect no more than 14.4 volts under any circumstances. And the high temperature of 125C (257F) seems way above any expected temperature that might be encountered under the hood of a vehicle.

I'll have to read the patents for more information.

Thanks,

Paul