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BF-3CR R1resistor Gets Hot


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Old 05-26-2011, 11:31:22 AM
aly9222 aly9222 is offline
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Default BF-3CR R1resistor Gets Hot

I replaced the OEM resistor 353-0057 and measured the voltage drop; it gets 14volts of drop and at 3.6 ohms the power dissipation is over 50 watts. The resistor is rated 25 watts only. Am I missing something? The generator dc voltage is 28 volts; that leaves the other 14 volts for charging the battery, fuel pump, etc.
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Old 05-26-2011, 12:49:12 PM
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Talking Re: BF-3CR R1resistor gets hot

What your missing is that, This is why these Resistors FAIL with AGE. It is a common ailment of these older Onan Gensets. Put in a 50 watt resistor and be done with it.
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Old 05-26-2011, 01:42:33 PM
aly9222 aly9222 is offline
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Default Re: BF-3CR R1resistor gets hot

Yeah I love to put a 50w resistor but couldn't find one that fits in there. Do you know where I can get one?

Also I am thinking of using a 24V relay to supply 12 volts to the gen accesories (fuel pump, ign coil, etc) and just disconnect the charging diode CR1, since the generator is connected to an inverter/charger that charges the batteries, including the gen battery.
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Old 05-26-2011, 02:35:32 PM
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Talking Re: BF-3CR R1resistor gets hot

I have used a couple of different fixes for this problem over the years.
First one was, to put a Dale solid Fixed Resistor in there and Heatsink it to a large chunk of metal, in the control box or Genend frame.
Second was, to put a full wave Bridge Rectifier in and then run it thru a Wide Input Range Dc/Dc Switching Converter that has a 12 Vdc Output at 6 Amps.
Both work, but the second if much more efficient and doesn't waste the power, by making a lot of extra heat.
Just say'en .... YMMV....
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Old 04-13-2018, 05:49:53 PM
wmrayt wmrayt is offline
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Default Re: BF-3CR R1resistor gets hot

Quote:
Originally Posted by aly9222 View Post
Yeah I love to put a 50w resistor but couldn't find one that fits in there. Do you know where I can get one?

Also I am thinking of using a 24V relay to supply 12 volts to the gen accesories (fuel pump, ign coil, etc) and just disconnect the charging diode CR1, since the generator is connected to an inverter/charger that charges the batteries, including the gen battery.
aly9222 How would this relay be set up to only give power when running?
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