Help with car battery charger HT7715

[R_J]

Re: Help with car battery charger HT7715

That is why I asked for a voltage check across the cap in post #10, If there is no voltage across that cap there is no secondary voltage so the click can not come from the relay.

Almost all pwm ic's will pulse the primary circuit at least once (click) this pulse should produce enough voltage across C24 to raise the vcc above the start threshold of the ic.
The Dc voltage should be measured across the outside leads of the bridge rectifier (+ and -) or just measure the voltage across the large capacitor in the primary. It should be around 325VDC

[budm]

Re: Help with car battery charger HT7715

It is 12vdc relay coil (OKS2C-S15DC12V).
See attachment as to what I believe how the relay is driven.
I would expect the clicking to be continuous if the power supply is stuck in start/stop loop if it is in protection mode or due to bad startup/running cap.
BTW, the click sound of the relay will be so much more metallic sound than the clicking of the SMPS circuit.

[ex250]

Re: Help with car battery charger HT7715

Changed the cap C24 with a new one, same behabior than before.

[R_J]

Re: Help with car battery charger HT7715

Check the voltage on C24, You must use the hot side ground, (- of bridge or - of primary cap). If you have o volts, (with power disconnected) check the resistor marked 104, and the resistor on the top side connected to it, also check the large 3 watt resistor next to the heatsink beside the fet.
If you can provide the numbers of the two 8 pin ic's that would help, they may be hard to read due to the coating

In the past did this charger come on when only pluged into the mains? or did it require the 12 volt battery be connected first?

[ex250]

Re: Help with car battery charger HT7715

On C24 0v readings, 104 reads variable values 102K and 95K inverting poles, the top side resistor is 100K and the bigger 3w one I need to desolder it, the reading is 0,001K

The charguer not needed to teh connected to the battery to power on, but without one conected only showed one icon on the display.

[R_J]

Re: Help with car battery charger HT7715

The large 3 watt should read as a short, Try changing the resistance reading to the lowest scale (usually 200Ω) but I guess 0,001k means it is ok. You can also check that small glass diode next to the 2R0 resistor, if it is ok, It could be that the ic is bad, because you should have some startup voltage on C24
Any chance you can read the ic niumbers?

You should have around 325VDC on the large capacitor, That 100k resistor on the top side is connected to the positive of that main filter cap and supplies voltage to the smd resistor marked 104, This charges C24 to around 10~20vdc. this is the initial VCC voltage supply for the 8 pin ic. once the circuit is working the VCC voltage is maintained via the transformer, that small glass diode and the 2R0 resistor

[ex250]

Re: Help with car battery charger HT7715

I am not able to remove the varnish, i tried with solvent and turpentine and nothing...seems "extra tough", I don't know any other way to remove it without erasing and deleting the IC chip letters.

The 325VDC are present, seems that the fail is at the IC, the diode is OK reading to one side and nothing on reverse, 2R0 seems good at 2,1 Ohms.

I 'm thinking to use some paint stripper liquid, let's see if it doesn't spoil anything too much...

Thanks for the follow up and help of this!

[redwire]

Re: Help with car battery charger HT7715

I use needle probes or dentist's picks to poke through the coating/varnish.

[maher471]

Hi, here is the schematic I made by reverse engineering for the HT7715 charger, I hope it can help

[petehall347]

Hi, here is the schematic I made by reverse engineering for the HT7715 charger, I hope it can help

might be long gone .it was 4 years ago