12V-6V Ultimate speed lead acid 3.8 B1 owners please read

Thread Starter

Mozee

Joined Jul 23, 2016
87
Hi,

I've bought an Ultimate Speed ULG 3.8 B1 12V 6V lead acid battery charger and fried the R14 and R13 smd resistors and I can't read their values. Kindly if some one has the same unit can indicate their values so I can change them.. any ideas would be appreciated.
 

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ScottWang

Joined Aug 23, 2012
6,926
You can waiting for the members bring you the same board, or maybe you can also draw the circuit around the area of R13, R14, R15, so we can try to analyze the circuit and give you the suggestion for the values of resistors, if there is bjt or mosfet on board is more easier to suggest the values, but if the ic without number then it's hard to analyze.
 

ian field

Joined Oct 27, 2012
6,539
This is another image

The mosfet is SSF10N60B n-channel 600 V
My guess is the parallel resistors are for MOSFET source current sensing - if you can't read the markings; the track under them has probably been vapourised.

If the MOSFET fails; it usually goes short circuit between all 3 pins, it dumps the reservoir capacitor into the source resistors and blows them away. Since the gate is also shorted; some of the charge escapes through the gate and destroys the chip.

When I serviced monitors for a living; some manufacturers used a 20V Shottky barrier diode as a gate clamp instead of a Zener - every once in a while the SB clamp protected the chip, the Zener clamp hardly ever did.
 

Thread Starter

Mozee

Joined Jul 23, 2016
87
@ian field
Hmm .. any ideas on the approx value of them? The only thing visible was the R letter on the resistor!!

The live "220V" is connected to the source of the mosfet! Also i checked it and all 3 terminals are shorted so it was actually fried!!

Can I use a 1/4w very small value resistor eg 100ohm??
 

ian field

Joined Oct 27, 2012
6,539
@ian field
Hmm .. any ideas on the approx value of them? The only thing visible was the R letter on the resistor!!

The live "220V" is connected to the source of the mosfet! Also i checked it and all 3 terminals are shorted so it was actually fried!!

Can I use a 1/4w very small value resistor eg 100ohm??
The source resistors could be less than 1 Ohm each. You can use whatever resistors can be made to fit - but the correct resistance value must be adhered to.

The source isn't "live" in the normally accepted sense - the negative half cycles come through the bridge rectifier to the rail those resistors connect to. Its certainly dangerous - if this was a project; it wouldn't be allowed on this forum.
 
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