I have 7 of these HF float chargers / automatic maintainers and they all work great. They do an excellent job of maintaining my batteries at about 13.2 Vdc. I also verified that they shut off charging current once they reach that state, but will pulse the batteries intermittently to maintain them at that level. There is a two color (red & green) LED on the charger that indicates what it's doing. The LED flashes red when it is disconnected from the battery or connected wrong, stays solid red when it is charging (about 750 mA), flashes solid green when it is nearly fully charged (still charging at 750 mA) and then flashes green when it is maintaining (intermittent pulses approx. 200 - 500 mA on DVM). As I said, they all work good EXCEPT on three of the chargers the green portion of the LED no longer functions, the red portion is fine. I verified that the charger(s) itself is still working, only the green portion of the LED is not.

The circuit board is very cramped (the LED is particularly hard to get at) but I was able to manage to "ohm out" both parts of the LED. Each side (red or green) reads about the same: 2.4M (ohms) one direction and 4.3M the other direction. None of the chips on the dual sided PCB are labeled. Following traces is impossible as many of the traces are covered by components and/or pass through to the other side of the PCB. A thorough visual inspections reveals no obvious things like cold solder joints, bad traces, burnt components, etc. Because this has happened on three chargers so far, I suspect that the LED (based on the ohm readings) itself is good but that there is some sort of driver chip or transistor that might be bad.

Any chance anyone has a schematic for this (can't find anything via Google) or has done any hacking on these? I maintain quite a few batteries in the winter and it's really handy just glancing at the equipment to see if the green LED is lit, if it's not, then I have to make sure nothing got knocked loose, unplugged, etc. Thanks!

 

I found a tear down of the Deltran Battery Tender Junior that looks similar to and apparently works the same as the HF Centec branded device:

Maybe that will help. According to the video, it has a microcontroller in it and a bipolar LED.

Edit: The HF manual does not mention a microprocessor, the Deltran manual does. Here's a link to the Deltran manual, if it helps: https://www.batterystuff.com/files/021-0123_man.pdf

 

I have and use 4 of these Harbor Freight float chargers. They all must have been bad from the get go, even though they keep my batteries up and healthy. I say bad because according to the TS, mine have never had any green flashing LED on them. Mine, bought over many years as needed, have always just been red with no flashing and light up when connected to the battery even if not plugged in at the time. I use them to keep my mower batteries topped off, keeps me from buying mower batteries since I started using them.

 

@shortbus
What you describe sounds like what I have been using for years too:



They go by a variety of SKUs, 42292 and 69955 are common. "List" price is $9.99 today, but they seem perpetually on sale for about $6.00. It does not have an MCU, but I have not had one fail, except for the box coming apart. A couple of screws fixed that. The schematic for the cheapie is on the internet.

I think the TS's charger is SKU 62813. SKU 63161 may be the same or very similar. Either is about $22 list. According to some blogs I checked, it has an MCU.

 

Hi Guys. Thanks for the response. I watched the video and the Deltran, from the outside, appeared to be identical to the HF model I have. Inside was a different story. First, it didn't have the relatively large power transformer. I suspect the Deltran may have a full-wave bridge circuit to get from 120 Vac to XX Vdc whereas the HF I'm thinking has a switching PS since its transformer is about 1/4 that size. I was surprised how much "stuff" was in the unit I disassembled, 4 - 5 IC's, and components mounted on both sides of the main PCB. There was also a smaller PCB with an IC on it mounted to the main PCB. There was no heatsink, but I never felt any of the wall-warts getting alarmingly warm even when outputting the rated 750 mA (ha ha, maybe that's what cooked the LED driver if that IS the problem??).

HF makes two chargers that look very similar. The 42292/69955, the cheaper of the two, I had initially purchased a number of years back. If I recall correctly, they didn't last very long (I can't remember exactly what the failure was), but when I opened them up they were quite simple inside compared to the 62813 ("Deluxe") version. Also, again if memory serves me right, they outputted what I thought was too high a voltage, some as high as 15.5 or so volts and they never seemed to turn off. The 62813's seem to stay under about 14.5 Vdc when charging and about 13.2 Vdc when maintaining. The 62813's also definitely shut off the output completely off when maintaining, only pulsing the battery now and then to maintain a full charge.

I have about $2k tied up in batteries on equipment that sees little use in the winter months. Thus my perhaps abnormal interest in these cheap chargers, but they work great! The "better" HF chargers (62813) have done an excellent job and are about $5 - 10 cheaper the Battery Tender JR, which I also have. BTW, the BTJR, while I have never opened it up is about 2 - 3 times the weight of the HF units though about the same physical size, probably due to the larger power transformer and heat sink.

Still would like a schematic for the 62813 on the outside chance I could actually find the bad component AND replace it!

 

I'd like to remove the LED and check it out of circuit. In-circuit resistance isn't helpful. Or, hook up a voltmeter and see if the green LED is getting power.