After starting my Chevy Duramax Deisel the alternator puts out over 15.5V and then drops down after a few minutes. This caused my 400W Portawatt inverter to drop out on high voltage. Is there a simple circuit using mosfets, 2n3055, etc and using readily available parts to drop the voltage down to
Your alternator should not put out that much, you need a new voltage regulator or maybe a new battery.
Thank you for your responses. A #1 welding cable runs from the engine batteries and feeds the 400 watt inverter in the cab. The buss then continues on to feed a 2500 watt inverter and 400 amphr deep cycle type aux. batteries in the back of the service truck. This setup is duplicated in two of our other sevice trucks and they also suffer from shut down of the cab inverter which runs a computer and test equipment. The 2.5K inverter is not a concern. This only happens on our deisel equiped trucks and GM assures us that this higher first recharge voltage is normal to a deisel due to its high output alternator. A resistive device is out as it only acts as a current limiter.
Hmm, a bit easier said than done. What's a good choice for the p-channel MOSFET, which should have Ron below 5 milliohms? This FET will have a rather high gate capacitance, mandating a proper gate driver. At which point the designer will begin considering the attractive n-channel MOSFET plus driver solutions.
And the low-resistance 50A inductor will be fun as well. Using a low-inductance part will help the designer to meet the low- resistance requirement, but this will mandate higher switching frequencies, which in turn mandates a serious FET gate driver.
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Thanks,
- Win
A few possibilities (through-hole packages only). Note the high gate capacitances.
part Vdss Ron Ciss number ohms pF ------ ---- ----- ---- IRF9540 100V 0.2 1400 IRF9Z30 50V 0.14 900 IRF9Z34 60V 0.14 1100 IRF5305 55V 0.06 1200 FQA47P06 60V 0.026 3600 NDP6030PL 30V 0.025 1570 MTP50P03 30V 0.025 4900 SPP80P06 60V 0.023 5033 IRF4905 55V 0.020 3400 2SJ555 60V 0.017 4100 STP80PF55 55V 0.016 5500 SUP90P06-09L 60V 0.015 9200 FX70UMJ 30V 0.012 11140 SUP75P05-08 55V 0.008 8500
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Thanks,
- Win
Not to mention blowing out the inverter filter capacitors with excessive ripple current....
It might be better to route directly from the engine batteries to the aux battery. Then distribute from the aux battery to the inverters. In this way the aux battery has a better chance of functioning as an additional shunt voltage regulator.
If the problem still persists then maybe a bit of brute force and ignorance would solve the problem.
Have two meaty diodes in series with the supply to the 400W device, with automobile-type high current contactors holding shorts across the diodes. If the upstream voltage exceeds 14.5V then unshort one diode, and unshort the other above about 15.5V. Have about a 0.5V comparator hysteresis. Maybe cool the diode heatsinks with a 12V fan when a diode is unshorted.
-- Tony Williams.
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