Still worried about too much Voltage

[skyguy59]

Going out again this weekend with second CDI powerpack. I asked a previous question about stator and rectifier outputs and have decided mine is working as advertised. I have also researched the forum enough to decide that 16 to 18 VDC is normal on unregulated systems. I have battery CD ignition from CDI with warnings about not exceeding 16 volts or damage to pulse pack will occur. Why would engineers put a voltage limited pack on an unregulated charging system? I notice the OEM pack says not to exceed 15.5 volts.<br />I would really hate to blow another pack. Just how sensitive are these Battery CDI packs to overvoltage?? <br /><br />Thanks in Advance<br /><br />Russ In Texas<br /><br />P.S. 1972 100 HP johnson

 

[R.Johnson]

Re: Still worried about too much Voltage

The one thing you might want to check is The amp reading between coil, and pack. When you replaced the pack, did you replace the coil? With a amp meter in series between the pack, and coil, the reading should be about 1 1/2 amps, and hold steady. A defective coil can also blow these packs. Have you carefully gone over all connections? It's important that you have a good ground to the pack, and a good ground to the engine itself. On an engine that age I would also check both battery leads that they are not breaking down at the point where they go into the cowl from the pivoting action of the engine. I am at a loss where you are getting that high voltage from, but I would take a look at those battery leads.Rapair recommends that you don,t use mainteance-free batteries with this system also.

 

[skyguy59]

Re: Still worried about too much Voltage

I have done all of the above. Yes I replaced the coil both times. Redid the battery cables , cleaned all of the connections, did the voltage drop checks etc, The thing is everything is normal and within spec and working correctly. A 2 volt margin just doesnt seem like much. So I ask again, How sensitive are these packs to overvoltage and why would an engineer put a voltage limited pack on an unregulated charging system?<br /><br />Russ In Texas

 

[P.V.]

Re: Still worried about too much Voltage

Go to your local, friendly OMC/BRP dealer and have him look up a "half-wave" regulator. I think a .... let's see..... probably a '73 or so 125 or 135 hp used one, or a ..... hhhmmm. a .....early 140 hp V-4 also!! It effectly charges 1/2 of "normal" so you will not have full charging and excessive voltage!!! A good parts man can find one in a bout four minutes of looking for it. I'll do some homework today for you!!

 

[ledgefinder]

Re: Still worried about too much Voltage

My understanding is that, as you say, the battery is the regulator on those 1969-72 V4s. Use a big battery and clean connections. <br /><br />On the other hand, I generally check motors to see if they're charging before I sell them, and I have never seen anything like 16-18V. Is that with the battery connected?? My memory's a bit vague, but I think I typically get 13 & 1/2 volts with motor running (fast idle) and 12 & 1/2 with it shut off.

 

[skyguy59]

Re: Still worried about too much Voltage

I'm seeing 13.5 to 14 volts at 1500. I realize that this is normal. If you read all of the postings on this board about overvoltage you will see why I asked the question. I know if it ain't broke don't fix it. Call me cautious, but then again, I never got towed in while running a Mercury.<br /><br />Russ in Texas

 

[R.Johnson]

Re: Still worried about too much Voltage

What type of instrument are you using to check the voltage? You say you have 13.5-14 volts at 1500 rpm, what is the reading at full throttle?

 

[skyguy59]

Re: Still worried about too much Voltage

I was using a calibrated voltmeter (expensive Fluke borrowed from work) to check the voltage while running it on the muffs. The volt meter in the dash is reasonably close to what the calibrated meter said. I just got back from running it for two hours in the bay and the volt meter in the dash never went over 14VDC even at full throttle. Like I said, maybe I was chasing Ghosts. Sometime I do that when I'm trying to understand a concept. Oh well better safe than sorry.<br />Thanks to all for all of the input. Thats whats great about this board, the information on here is priceless.<br /><br />Thanks again<br /><br />Russ In Texas

 

[R.Johnson]

Re: Still worried about too much Voltage

Russ: I can understand being spooked with a problem, what with what those battery CD packs cost. Plus! nobody likes being stranded.

 

[ledgefinder]

Re: Still worried about too much Voltage

So, with the battery hooked up, you never see over 14V (at least on the dash meter)? The 16V-18V you cited before were readings off just the stator, with the battery disconnected? Have I got it straight now? <br /><br />Sounds perfectly normal to me, go ahead & run it. You've got a good big battery on it, right? - should be fine. BTW, I have seen plenty of blown CD packs on those 1968-72 battery CD systems, but they were all original equipment. I have yet to see a Rapair blow, or any replacement box for that matter.<br /><br />How about checking with Rapair on this. Didn't they give you a replacement on the first one that blew?

 

[skyguy59]

Re: Still worried about too much Voltage

Yes Rapair couldn't have been nicer. They are super people to deal with who stand behind their product. I talked with the tech and they preapproved the warranty and I had a new pack the next day. When I told the tech that the timing was very erratic on the first pack she said it sounded like a weak transistor. ( I had attributed it to the borrowed timing light) She even apologised because I got towed in. The 16-18 Volts was the AC reading across the stator leads with the engine running at 1500 RPMs. The 14 Volts was DC measured at the red lead on the rectifier. Battery was never disconnected while running, I'm told thats a no-no. After reading posts on this board I reasoned that since the rectifier wasn't a regulator the voltage could concievably get to high and cause problems. I tend to over-analyse things I don't completely understand.<br />Thanks again for all of the responses.<br /><br />Russ in Texas <br /><br />4 useless things to a pilot, The sky above you, the runway behind you, the gas you left on the ground and the question you didn't ask!

 

[ledgefinder]

Re: Still worried about too much Voltage

So you are seeing 16-18V with the battery connected? I would check with Rapair, then & see what if their tech people can give an authoritative answer.

 

[BoatBuoy]

Re: Still worried about too much Voltage

I seem to remember that DC voltage out of a full-wave bridge rectifier is something less than the AC feed. Seems like the square root of two has something to do with it. Any EE's out there?

 

[skyguy59]

Re: Still worried about too much Voltage

Ledgefinder, the 16 to 18 volts is AC from the stator not DC. The book says stator output should be between 16 to 20 VAC which it is. Output DC from the rectifier is 13.8 to 14DC which is also correct by book spec. BoatBouy, you are on the mark, I checked with our avionics tech and he said that there will be a voltage drop across the rectifier, around 25% or so. However, the higher the input AC Voltage the higer the output DC Voltage as it is not a regulator. He also said that the stator should become "saturated" at a given RPM and not produce any more voltage regardless of increasing RPM unless the Amp rating of the stator (load on the electrical system) is exceeded. If you exceed it long enough something will eventually fail, powerpack, rectifier or stator.<br />At least I think I halfway understand the way it works now. (Sure would have been nice if he wasn't out of town last week)<br /><br />Russ In Texas

 

[Jcrain]

Re: Still worried about too much Voltage

Do you work in Rockport?

 

[skyguy59]

Re: Still worried about too much Voltage

CRP, live in AP, keep my airplane at T43.<br /><br />Russ In Texas

 

[Jcrain]

Re: Still worried about too much Voltage

ok, thanks. Wrong Russ

 

[walleyehed]

Re: Still worried about too much Voltage

As long as DC output is not over 15.1-3, it's doing what it's meant to. If AC is within spec, as I read you saying, I don't see a problem.<br />By the way, your stator actually has a curve charge where it starts to drop off, but nearly imeasurable.<br />Watch out for the avionics techs...they are trained in one field only....if it's a doulble field, they're in trouble..