Try Using [img thumb] for big images.
| | | quote | Originally posted by Chris Eddy:
The Ron does have to be right.. lowering it would require gaining it up. And raising it would cause more heat.
The right idea is to not use Ron as a current sensor.. it varies in production, and is a poor way to do it. |
|
Yes but GM allows some variations... So 90mΩ might work fine but nte2389 et al 1/2 of Ron is far outside this and quickly kills the system. (90mΩ may trip Load Sense a bit early cause fake Jam Motor(s). More so w/ iffy motors and HL lift parts.)
Not ideal for fixing but design works for decades now and was cheap to make.
GM have Millions of modules that last for years and likely < 1% fails is a very good rate. 87 & up Fiero Sunbird Firebird Corvette etc have same type of module w/ minor versions. You don't see many things now w/ < 5% fail rate in ~5 years. Many are dead in 1-2 years like many iThings from Apple.
If you fix a Dead MOSFET board... Look for other problems causing a fried FET...
Example: Cliff's original one shows signs got wet at minimum. Plugs aren't "Water Proof" just weather resistance and water can still get in thru plugs or case "glue." (glue is likely old type "windshield sealer" and often doesn't seal well.) Water could make board to swell etc causing FET w/ no or poor connection to heatsink. Heatsink is copper on the other side of board. (Is enough heatsink for short duty cycle the FET is on.)
If board shows signs of water then can have other parts w/ damage too. Resistors etc can change values etc and fried MOSFET as a side effect.
Crack solder joints anywhere can do same... Load Sense won't get good "data" and might not see the real loads and doesn't shutoff the MOSFET. Even if LS is very simple and resets the "timer" chip. (Very likely) Load won't reset because iffy joints etc.
So while you can try to fix... Don't use it until you make sure the Load Sense works. If LS does not work then Timer runs full power to motor(s) every time goes up/down at End of Travel for 2-5 sec. That bad enough but If Timer fails then you quickly will have fried the module and likely the motors and wiring to them.
The board and the chip uses capacitors and caps can fail just from old age. Is why Many Fiero Tach fails.
Digital module? Can likely use 556/558 timer and "better" load sense circuit to reset the chip.
Likely relay is shut off too to save coil lifetime and not eat power when motors are done.
One ways to sense load is a small coil w/ reed switch or hall effect sensor. Pull enough power thru the coil and switch/sensor trips resetting timer...
Many Digital items use a lot more power. HL module only uses a very few mA for the one chip in side. More "standby" power eaten by ECM etc the less time before you have a dead battery.
[This message has been edited by theogre (edited 10-01-2017).]
