Next Step Runaway - New Problem

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Next Step Runaway - New Problem

Postby petedd on Tue May 26, 2015 5:59 pm

I have a Next Step Regulator S/N N13708 which has been utterly reliable for many years. Yesterday though it drove the alternator to over 17 volt output. I have conducted the trouble shooting routine. All voltages are appropriate except that the field current just builds and builds and follows the alternator output (battery) voltage until it is way over voltage. This is a new behavior. I have four other sources of charging my batteries: solar, wind, 12V genset with Next V3 Regulator. I first thought that one of these could be interfering so I disconnected all and there was no difference in behavior. I also checked the resistance of every wire to the regulator and even changed the fuses in case any might have been marginal. No change. Every time I start the engine, the field voltage runs away or just runs at the level of the battery voltage, building and building to extreme voltages. The field current is not be regulated. I also thought there might be a short at the alternator so I isolated the alternator by removing the field wire at the regulator (with the regulator turned off). The alternator operates as expected... no voltage is generated without a field voltage provided.

Is there a component in the regulator which may have failed? (It is as if the control to the field current output locked high or the field current output is shorted to the B+ voltage). There are no obvious signed of the magic smoke having escaped from any of the components.

Thanks for any help you can provide.

Pete
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Re: Next Step Runaway - New Problem

Postby Coulomb on Tue May 26, 2015 6:06 pm

Field voltage should not be present unless the ignition input is active. You don't need to run the engine to conduct this test, but the alternator field wire must be connected to the regulator.

If the regulator field output doesn't go on and off with the ignition input, then most likely the regulator has failed.
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Re: Next Step Runaway - New Problem

Postby petedd on Tue May 26, 2015 7:40 pm

Thanks for the quick reply. Sorry if I did not clarify adequately. If the on/off input is low (~zero volts), there is no field output voltage. If the on/off input is high (battery voltage), then the field voltage is high and just gets higher and higher tracking the voltage of the alternator output until it maxes out over 17 volts (or at least that is as far as I have let it go before I turn it off). Still a failed unit? What would cause such a failure? It's been so reliable for so many years.
petedd
 
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Re: Next Step Runaway - New Problem

Postby Coulomb on Tue May 26, 2015 9:15 pm

Disconnect the wire T+ on the regulator and see if the problem persists.

If so, the regulator must not be sensing battery voltage correctly and will have to be replaced.
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Re: Next Step Runaway - New Problem

Postby petedd on Wed May 27, 2015 6:25 am

OK, I will reinstall and test with the temperature sensor positive disconnected. Assuming it still fails, I would want to find out what would have caused the unit to suddenly fail lest I buy a new one (or should I have this one repaired) and have the new (or repaired one) blow up also. In other words, what should I check or fix before installing a new regulator and potentially having the new one fail as well?

Thanks,

Pete
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Re: Next Step Runaway - New Problem

Postby petedd on Thu May 28, 2015 6:52 am

FIxed with a 1.5 cent resistor. I noticed that one of the 1K ohm resistors off of the BAT lug on the regulator looked a bit discolored. I checked it with my VOM and it was open. Clearly the regulator was not seeing the battery voltage as a result of this open resistor. I replaced it. It took longer for the soldering iron to heat up than it did to diagnose and repair this.

I still wonder what would have caused this failure. Have you seen this before? Any thoughts on the root cause?

Thanks again. Still love your products.
petedd
 
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Re: Next Step Runaway - New Problem

Postby Coulomb on Thu May 28, 2015 11:33 am

Sharp eyes and good luck. You may be good for another 20 years.

Overheating is a sign of some high voltage transients. Have you read this: http://www.amplepower.com/primer/burnt_sw/index.html
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