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voltage runaway

PostPosted: Wed Jul 23, 2014 3:54 pm
by JSally
I had this problem of voltage runaway early this year. All the trouble shooting values were normal. The fault was intermittent. We bought and installed a new NS2 in Feb. Everything was OK until now and we have the same problem again. There is nothing else changed in the system. All the readings for the troubleshooting guide are correct. Can the new NS2 be faulty?

Re: voltage runaway

PostPosted: Wed Jul 23, 2014 7:08 pm
by Coulomb
It's unlikely that you'd have two units with the same intermittent problem.

This condition can exist when batteries are fully charged and there is little or no load on the system. Some alternators have enough residual magnetism to excite the alternator a little.

Can you put a load on the system when this happens and see what it does?

Re: voltage runaway

PostPosted: Thu Jul 24, 2014 4:56 pm
by JSally
I checked settings and covered the solar panels then started up. Voltage went up to 15.6 at 1200rpm. Applied load - voltage came back to 13 7 - 14.0. Stopped load and voltage went up. Applied load for longer but the outcome was the same. I am concerned for my batteries which are new [very expensive] AGM. I do not want to risk cookimg them.

Re: voltage runaway

PostPosted: Thu Jul 24, 2014 7:29 pm
by Coulomb
That sounds like fully charged batteries and residual magnetism in the alternator. What alternator do you have?

Re: voltage runaway

PostPosted: Thu Jul 24, 2014 8:14 pm
by JSally
It is a 120Amp Bosche alterantor. when tested this AM the batteries were not full - down 40AmpHrs from overnight.

Re: voltage runaway

PostPosted: Thu Jul 24, 2014 8:31 pm
by Coulomb
What were the alternator Amps and battery Amps at the time?

What are you using to determine Amp-hours?

What is the capacity of the batteries?

Re: voltage runaway

PostPosted: Thu Jul 24, 2014 8:49 pm
by JSally
This AM used BEP monitor for battery Volts but have tested with Mulitimeter
Use BEP monitor to assess battery AHR - total battery bank capacity 710AHr - this AM 672. That usage overnight is usual based on 10years living on this boat.
Alternator Amps - written on the unit

Re: voltage runaway

PostPosted: Thu Jul 24, 2014 9:48 pm
by JSally
further info - charging amps about 30 - went down to about 5 when load applied. BEP monitor gives this info

Re: voltage runaway

PostPosted: Fri Jul 25, 2014 10:47 am
by Coulomb
How was the Bosch alternator modified to work with an external regulator?

Re: voltage runaway

PostPosted: Fri Jul 25, 2014 12:42 pm
by JSally
I dont know the exact process but it was done.....we had the installation done by an marine electrition. I will remind you that we have been on the boat 24/7 for 10years with this set up. Originally we had a NextStep. The original alternator was replaced in 2012 with another the same. This problem started 2014. We did not get a diagnosis but purchased a NS2 as we were in a remote area without access to marine elactritions, The new one has worked until now.
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