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Voltage problems

D

double_g

Contributing Member
"Howzit gents,havn't been

"Howzit gents,havn't been on here a while due to the repairs I have done on my AQ131D. I have done alot of work as far as changing the below deck fuel tank, overhauling the bottom half of my b230. I installed the elect. ingnition and changed alot of parts. The cooling system has been checked from back to front to back again. I replaced the transom hose, the hose connector, the seals in the leg. getting good suction from the sea water pump and the circulation pump is working good because I took the thermostat out to check the circulation. anyways I replaced the water temp sender also. This is the problem. When I go fast the water temp gauge climbs to 240 degrees within one minute and then drops when I slow down. When it was at 240 degrees on the gauge the heat gun was at 204 degrees. I bench test my water temp gauge and found out that the temperature follows the voltage. when at 12 volts it staid at 180 degrees but when increased to 14 it went up to 240. it did this on 2 seperate gauges. A teleflex and a brand new volvo gauge. What is the voltage suppose to be at the dash gauges? and is there some type of regulator or resister that goes to the ignition switch. I can not find one anywhere in my wiring but the manual shows it from the alternator to the ignition. last question if I need one where can I order one?

thanks,

Barry G."
 
"Forget about the resistor. Th

"Forget about the resistor. That is not your problem. Remember, sending units come in several types. The unit <u>must</u> be matched to the specific gauge and to the number of stations."
 
"Thanks Dennis, but I went dow

"Thanks Dennis, but I went down to my boat today and decided to do some continuity tests and found out that I have no continuity between the alternator wire that is suppose to have the resistor and the instrument lighting switch. I did buy the gauge and temp sender from the same volvo dealer. Both are volvo parts that is suppose to match. Called another dealer and he said if I did not have this resistor my engine would not shut down. Is this true?"
 
"There is a resistor at the th

"There is a resistor at the third terminal of the alternator. This resistor is needed to drop the voltage supplied to some French alternators and thus to "excite" the magnetic field produced by the rotor windings. What does this have to do with engine temp? Did I miss something? BTW, the gauges do not care whether their line supply is 12 or 13 volts. It is irrelevant. There is no resistor at the ignition switch or dash panel. Fuzes, yes. "
 
"The resistor at the field ent

"The resistor at the field entry of the alternator is there only to reduce current and amps to the electrical system (read coil) when engine is shut off. Remove it and engine will continue running. It might be replaced with a 'charging light' at the instrument panel and the bulb itself will work as a resistor. In this case the field wire must run from instrument panel directly to alternator and not been taken directly from the engine wireing harness.
Temp gauges are nothing but ohm-meters with different name. Temp senders are resistors that varies the resistance with temperature. For it to work as intended the wireing harness betwen senders and gauge must have 0 ohm resistance or the reading will be wrong. Typically dual engine installations will often have different readings on stb and port engine due to different resistance in the length of the harnesses. Voltage in the system should have minimum influence of the reading providing there is 0 resistance in the harness from instrument to temp sender. The only cases when voltage might be an issue is if the support to the instrument at 'ign on' engine not running is below around 12 Volts, too low for the instrument itself to work properly."
 
"Let me go a little further an

"Let me go a little further and explain why this is kicking my tail. I work at a power plant and had one of the electricians test 2 seperate gauges. 1 teleflex water temp gauge and 1 volvo penta water temp gauge. when we put 180 degrees of heat on it at 12 volts it staid at 180 degrees. when we increased the voltage to 14.5 both gauges climbed up to 240. when we decreased the voltage back to 12 it went back down to 180 degrees. The thing I don't understand is it is only that one gauge. when I did a test run, the temp. was at 240 and the laser heat gun only went up to 204 degrees on the head and the heat exchanger neck. I do realize that the coolant is probably a little hotter but I wouldn't think 30 to 40 degrees. Engine is running fine. The gauge does move up pretty fast once the boat starts going fast. What about using a mechanical gauge for testing?"
 
"Did the gauge 'jump'

"Did the gauge 'jump' to 240 when switching to 14,5 V or did it 'trail' a bit? The normal voltage for the system should be 13,8 -14,2 Volts. Did You test with one or two temp senders?
If the senders 'leak' the amperage going through might encrease heat and thereby resistance. But at the end the accuracy of the instruments are not that great. Call them temp indicators. If engine is not running too hot, leave it and keep track of readings out of normal. The Volvo OHC engines runs very close to 100C (boiling) and be sure the heat exchanger cap is correct and seals properly and use coolant mix and not pure water."
 
"I don't agree with anythi

"I don't agree with anything mort said (sorry). The resistor at the alternator has nothing to do with the coil or running of the engine. Its only function is to supply 3-4 volts to the rotor. The "excitation" circuit in the alternator can only operate at low voltage.

My experience is that temp gauges are fairly accurate. Differences of 5% are seen due to manufacturing tolerances of the thermistors (senders).

The normal running temp for a 4 cyl OHC is 185-195F.

Dual stations require a special sending unit. This is because the gauges are wired in parallel. It has nothing to do with wiring resistance per se.

Gauges, when connected to the correct sending unit, are not voltage sensitive due to internal bridge circuits which compensate for expected variations."
 
"Gents, I would like to shed s

"Gents, I would like to shed some light about the topics under discussion.

When it comes to gauges, no manufacturer would remain in business if the gauge reading would be significantly altered by small changes in the ship's voltage (unless, of course, the gauge under discussion happens to be a volt meter
biggrin.gif
). Most 12V electric gauges are designed to operate at a nominal voltage of about 14 volts and to operate reliably between about 11 and 16 V. As an example of this, here is a specs chart from Faria Instruments (oen of the brands I regulaly use).

http://faria-instruments.com/site_manuals/Tech_Specs_A.pdf

So Barry, if your gauges are giving you grief, you may want to consider using Faria temperature gauges. They are not expensive and, in my experience, they are reliable. Here is a table with the senders' resistances:

http://faria-instruments.com/site_manuals/IS0085E.pdf

Now, to the alternator resistor issue. Some of the alternators installed by Volvo Penta in the 70s and 80s were brushless. The advantage of those alternators is that they don't have a commutator, which means there is no wear or shorts between copper contacts, no brushes to wear, and no arcing between brushes and commutator. Unfortunately, one disadvantage is that they are not self-exciting, and therefore they need an external source of power to exciter field coils so that they can start working. That power is supplied from the battery and it is needed at the moment the engine is about to start. To simplify the wiring, Volvo Penta utilized for the exciter coils the same wire feeding the ignition coil, but this design has a setback: since a brushless alternator does self-excite after it is running and generating voltage (the supply of the external power from the battery is onle needed for the initial excitation of the field coils), it means that the voltage from the exciter can now backfeed the ignition coil once the ignition switch key has been turned off, which means the engine will continue running unless that voltage is interrupted or made so small that it does not generate sufficient voltage in the coil to create spark strong enough in the spak plugs. To deal with this problem, Volvo Penta installed a resistor (about 71 ohms) in the purple wire going to the alternator exciter terminal. After the ignition key has been turned off, that resistor makes the backfeed voltage from drop below the minimum voltage the coil requires to keep the engine running."
 
"El P, Volvo felt free to join

"El P, Volvo felt free to join the feed wires to the alternator and the coil only because the required 60 ohm resistor to feed the alternator rotor was effectively an open circuit as far as the coil is concerned. They did not try to simplify the circuit just so an expensive ($35) resistor could be installed."
 
"Ok, thanks guys. I will do so

"Ok, thanks guys. I will do some more testing and let you guys know the results. the volts on my boat was around 13.8. I do have the flame thrower coil but this has a built in resistance so It shouldn't be the problem."
 
"Dennis, I don't think I u

"Dennis, I don't think I understand your latest remarks, which by the way I don't think are adding anything meaningful to the discussion. There are many ways of interrupting the voltage to the exciter terminal: a diode, a relay, a SCR, an ignition switch with 4 terminals instead of 3 are just a few examples. When considering that in the late 60s and early 70s anything that had to do with electronics was avoided as the devil for marine applications, the resistor seemed the simplest choice in the particular application we are talking about, though not necessarily the most effective. Therefore, I still think that Volvo Penta included one and not another gadget in order to keep the circuit simple, as any other option would have made it more effective but also more complicated.

By the way, I believe you meant to say "stator" when you talked about feeding the alternator "rotor". Stators are "static" and don't move, while a rotor "rotates". There is nothing to "feed" in an SEV Marchal alternator rotor, for all the windings are located in the stator."
 
"I test ran my boat while sitt

"I test ran my boat while sitting at the dock and after installing a new wire from the alternator linked with the positive coil it won't shut down. I had to pull the wire off in order to get it to shut off. While the engine was running the temp. ran up to 240 with a steady increase and this was within 2 minutes. motor wasn't even warm. I put my hand on heat exchanger and was cool to the touch. I am thinking it's the sender though this is new. both Gauge and sender are new. Can I just install a resistor at 71 ohms, even if I have to link 2 together, or should I just get the volvo resistor. I realize that the resistor is not the gauge problem but would like to correct the areas needed also. Last but not least the water in Hawaii is warmer than the mainland so I would think it would run a little warmer. would this make sence? I'm in the ocean only with this boat. I appreciate all the responces from all of you because it helps me to understand the situation for trouble shooting the problems.

Thanks,

BG."
 
"A normal resistor (my gue

"A normal resistor (my guess is that it should be at least one watt or higher) may do the trick for awhile. However, being that resitor single wire and not properly insulated to withstand moisture and vibration, you are taking your chances, and I don't think that either Coast Guard or your insurance company would like it. Personally, I would go with the VP resistor, which is coated in rubber and can stand vibration and moisture.

What happened to your old resistor? Shouldn't it be in the old wire that ran from the alternator to the coil?"
 
"El P, maybe you can understan

"El P, maybe you can understand this. The maximum power allowed to the rotor winding is 1/2 Watt (0.15 amp, 3 volts). If the external resistor is removed the mechanic won't have to worry about run on. Should 12 volts be applied to the excitation terminal the rotor will burn out. It may take a minute or more depending on the quality of alternator."
 
"El, I found the resistor. I g

"El, I found the resistor. I guess when I was testing the old wire it was on the clip before it. I hooked it up and test ran boat. I had another digital gauge that I had installed the temp. sender that came with it on the side of the block and it did the same thing. I'm starting to think that maybe it is heating up. You had mentioned in one of the previous post that maybe the circulation pump is backwards. If this was the case would the motor run hot when idling or moving slow? the circulation pump is the only thing that i havn't messed with. Maybe it's slipping at higher rpm's."
 
"EL, Also I forgot to ask, cou

"EL, Also I forgot to ask, could I have damaged something with not having continuity with that wire that was bad? It's like the wire wasn't hooked up. motor was running and shutting off. boat did the same thing after I had fixed wire and reinstalled the resistor."
 
"Barry, I don't recall men

"Barry, I don't recall mentioning the circulation pump being backwards. Are you sure it was me? Nevertheless, the main sources of overheating are a corroded raw water hose connector in the outdrive, a defective impeller in the raw water pump, a fouled raw water strainer, a choked heat exchanger, and an exhaust manifold scaled-up or with mud in the circulation passages. Also, a defective circulating pump or a loose belt can lead to overheating. And obviously, a faulty thermostat.

Regarding the wire that was bad not being hooked-up, what would have happened is that the alternator would not have charged the batteries, as no power would have been supplied to the exciter coils."
 
I have 2 different AQ131 manua

I have 2 different AQ131 manual and one of the wiring diagram says to run the alternator wire and coil to the lighting instrument panel and the other says run it to the key switch. Does it matter? right now it is hooked up to the instrument lighting switch.
 
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