DC voltage increases with new Generator Running

[smokey73]

Just insalled a "used" Nextgen 5.5 KW generator. When the generator is running the DC voltage slowly increases from around 12.5 V (or whatever it is after the start) to about 16.25 Volts after the Generator is started.
DC Connections: It is wired with the start battery for the Generator as the House Battery. The positive comes from the switched side of the ON/OFF House Battery switch to the positive connection on the starter solenoid. The DC Negative goes from the boat negative bus (same place as the house battery negative) to a ground point on the generator. There is a start/stop loom and switch that is run from near the switch panel at the Nav Station to the generator connections. Everything seems to be straightfoward for that hook up and according to the NextGen owner's manual.
AC Connections: The green (ground) and white (neutral) are connected together at the generator as shown in the Nextgen Manual. The Power (black) and Neutral (white) go to the Sterling manual switch and from there to the AC breaker on the panel. The green from the generator goes to a connection on the boat side of the AC galvanic isolator (from there to the shore power green connection at the 3 pole AC Power switch at the Nav Station.

All these hookups are as shown in the NextGen manual and the Sterling Manual switch instructions. So why do I get DC voltage increasing when the Generator is running? I've actually measured 16.28 Volts at the battery when the Generator is running? Help!!!

 

[smokey73]

Just for info I am not running it now until I can get this sorted. Just trying to get a head start on what to look for. On the AC side, (with the AC switch in the on position) I get infinite ohms (open) measured between the white and green when the Sterling Power Selector switch is in the 1 (Shore Power position) and no shore power cable connected (which is what I expect to see). When the Sterling Power Selector Switch is in the 2 (Generator) position and the AC Power switch on I measure 0 ohms between the white and the green wire (which is also what I expect) The only thing I can think of is some sort of poor connection that is allowing some sort of DC leak. There is a Dynamo (dc generator) on the Nextgen but I'm not sure how it would act as a charger for the DC system.

 

[centerline]

could this be the reason it is "used"... maybe someone else had the problem and got rid of it?

I bet if you got on the nextgen website and got a hold of someone in tech support, you would get an answer in a hurry... the regulator/sensing wire is probably faulty. I doubt its an expensive problem, but it is a problem that needs immediate attention.

 

[Bob 04 H260]

Is anything being powered on the AC panel when the generator starts up ? Like a battery charger, inverter/charger ? Kind of odd as this set does not have a 12 Volt alternator or way of generating 12 V as far as I know. It needs a 110V battery charger to recharge the start battery.

We have a Nextgen 3.5Kw and have not seen this. I did not install it so I'm not too familiar with how it was wired up. We do not have a transfer switch or inverter to automatically switch. The transfer is done on our AC panel so that the main breaker for the shore power must be off in order to turn on the breakers from the Nextgen.

It does use the house bank to start the Nextgen. We do have a 12V disconnect switch to remove all dc power from the genset when servicing it.

I won't be on the boat until about Jan 7th or so. At that time I would be happy to trace out any wires or do any measurements needed. good luck, Bob
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[kloudie1]

Yeah, like Bob says, unless your unit has the (rare) optional 12V charger, then there is something going wonky in your 110V battery charger.. Even if the 110 V circuit is having changes in voltage, the 12 V stuff should be basically unaffected.. The battery charger has (usually) enough internal 12V regulation to keep that voltage inside the charger parameters.. Is the charger in a compartment that is getting hot inside when the genset is running?

 

[smokey73]

Yeah, like Bob says, unless your unit has the (rare) optional 12V charger, then there is something going wonky in your 110V battery charger.. Even if the 110 V circuit is having changes in voltage, the 12 V stuff should be basically unaffected.. The battery charger has (usually) enough internal 12V regulation to keep that voltage inside the charger parameters.. Is the charger in a compartment that is getting hot inside when the genset is running?

There is no 12V optional charger installed. I have not run the generator enough to get anything hot, and besides, I have not energized the 110V battery charger from the gen set. When I have test started the generator, all the AC switches were off, including the 110V battery charger. I can't figure out what is providing anything to the 12 voult system. I have to do a little more research but it looks like there is a 12 volt "dynometer" on the generator but I'm not sure of its purpose. There may something in the regulating circuit for this that is causing it to put out 16 V instead of 12 V but I'm still not sure how it gets to the batteries. Since its Christmas I can't get in touch with NextGen but I'll give them a call on Monday. Hopefully I can get this sorted in short order.

 

[centerline]

some models of the generators had an option for an alternator to charge the battery... not all of then had the option, and you are saying that yours does NOT have this option, correct?..... because the wire that goes from your house batteries to the starter on the generator to start it up, is the link that would carry the charge voltage back to house bank once its running, if it had the charging option built into it .

 

[smokey73]

some models of the generators had an option for an alternator to charge the battery... not all of then had the option, and you are saying that yours does NOT have this option, correct?..... because the wire that goes from your house batteries to the starter on the generator to start it up, is the link that would carry the charge voltage back to house bank once its running, if it had the charging option built into it .

Agree, the only reasonable path back to the House Battery from the Generator to the Battery is the red 12V wire on the starter. There are three pulleys driven by the belt on the end of the generator so I'm starting to believe that one of these is a 12V "dynamo" (dc generator) and there must be something askew in the output regulation from this. When I get back to the boat this weekend I'll start checking that out. Hope Nextgen can tell me what I need to do to sort this and get the output at the correct voltage if there is a 12 volt engine driven generator on this. If it is, I may just install a separate 12V starting battery for the generator.

 

[centerline]

Hope Nextgen can tell me what I need to do to sort this and get the output at the correct voltage if there is a 12 volt engine driven generator on this. If it is, I may just install a separate 12V starting battery for the generator.

keep in mind that if you do have the "charging" option on your generator, then it is obviously faulty, and putting it on its own battery without making a repair to the regulating circuit will still allow it to take out the battery, and at a quicker rate because there is only one battery taking all the load thats being delivered.

 

[smokey73]

keep in mind that if you do have the "charging" option on your generator, then it is obviously faulty, and putting it on its own battery without making a repair to the regulating circuit will still allow it to take out the battery, and at a quicker rate because there is only one battery taking all the load thats being delivered.

Of course, I did not mean to imply that I wouldn't fix the voltage regulation issue. Just that if there is a charging option, I might go ahead with a separate generator starting battery, just to give some redundancy to the starting capability so that if the reason I have to start the generator is a problem with the house battery, I'd still be able to start the generator to recover. The way my house and engine starting batteries are located and wired, to be able to use the propusion engine start battery means some fairly new runs of heavy battery cable and switches ($$$$) where adding a generator starting battery is much les expensive (that is if the Nextgen has the charging option installed aready)

 

[Bob 04 H260]

I don't know what the differences are with the Nextgen models. I've attached the manual for ours. I keep pdf's of all our manuals on my iPad.
Looking at the diagrams I don't see any connection between the 12 V power and the AC alternator. I don't know how they excite the alternator but they don't indicate any 12 V connection going into it. They do say the battery used to start it needs a 110V battery charger.
I'm afraid this does not help much unless there is something in this manual that explains something your does not.
Let us know what Nextgen says, good luck, Bob