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Old 10-21-2013, 06:24 AM   #21
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with my large capacity alternator running off the 80-h.p. engine. The 24-volt system can't hurt

The service ON time of a thruster is to protect the motor from overloading/overheating, not to protect a battery bank.
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Old 10-21-2013, 04:31 PM   #22
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So, today I checked the charging current from the 135amp alternator on our 280HP Cummins at idle. No other power draws were on. Current was read from the Link 2000. Idle is about 650rpm (vs. 2,600rpm WOT) At idle there is negligible charging current and the Cummins ammeter is on the cusp of showing discharge. At 850rpm, there is still barely any charging (2 amps), and this does not change much at 1,000rpm. There is nothing wrong with the alternator. It charges up to about 80amps when needed, though I have never seen anything close to 135amps, so I am guessing we just do not spin it fast enough for max output. Also, it is my understanding that alternators have a minimum RPM before they kick in. But the point of this posting is to confirm that the alternator makes negligible difference at idle in terms of powering a bow thruster.
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Old 10-21-2013, 04:36 PM   #23
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You are never going to power a bow thruster with an alternator!

Even if your alternator was putting out 135 amps, there would still be a 200+ amp deficit. Your alternator is fine, your wiring is deficient.

Like I said before, all your alternator has to do is charge the batteries which will be down somewhere less than 10 amps (based on my assumptions).
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Old 10-22-2013, 06:45 AM   #24
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I would like to know what you learn about the reading on the Link 2000. I have a similar reading at idle as you describe but no problem with thruster with two 8 D's and about a 20 ft. run of cable. Still, my old thruster is pretty tired. I would love to know what you replaced and what you have now. Did you need to do much tunnel work? Single or double props?
I replaced with the same unit I had, a Side-Power, by Sleipner Motor. It is model SE 60/185 S with a single prop. New alternator installed yesterday afternoon. Leaving Great Bridge VA for Coinjock NC this morning. Alternator was bad, very weak-so we will see how it goes today.
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Old 10-22-2013, 08:31 PM   #25
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My 24-volt Max Power thruster supposedly will give a 10-second warning between alarm and shutdown. The manual says maximum (continuous?) running time is between 2 and 3 minutes, depending upon the ambient temperature. Have never reached that point or loss/reduction in power. The thruster has a 125-amp fuse. ... Maneuvering out of a strange/tight slip and fairway today, requiring a 180-degree swivel, needed about 10-12 seconds of thruster operation.
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Old 10-22-2013, 08:33 PM   #26
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So, today I checked the charging current from the 135amp alternator on our 280HP Cummins at idle. No other power draws were on. Current was read from the Link 2000. Idle is about 650rpm (vs. 2,600rpm WOT) At idle there is negligible charging current and the Cummins ammeter is on the cusp of showing discharge. At 850rpm, there is still barely any charging (2 amps), and this does not change much at 1,000rpm. There is nothing wrong with the alternator. It charges up to about 80amps when needed, though I have never seen anything close to 135amps, so I am guessing we just do not spin it fast enough for max output. Also, it is my understanding that alternators have a minimum RPM before they kick in. But the point of this posting is to confirm that the alternator makes negligible difference at idle in terms of powering a bow thruster.
Wouldn't the output of an alternator be dependent upon the current draw?
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Old 10-23-2013, 06:03 AM   #27
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Reading the spec sheet for many alts show they can be run at 6000RPM and many smaller units rated for even higher RPM.

Sadly the front pulleys offered for many diesel marinizations will not allow the higher speeds to be reached.

This causes output at idle to be minor .

The stock V reg is little help as it was designed to maintain batts not charge heavily near idle.
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Old 10-23-2013, 07:04 AM   #28
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As long as the rpm of the alternator is at or beyond its "self sustaining" speed (around 2000 rpm for automotive style units) the output is dependent on the resistance of the loads it is powering and the ability of the field to carry excitation current without overheating.
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Old 10-23-2013, 01:24 PM   #29
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The old unit would not rev very high and would quickly drop the volt meter below 10 volts. The new unit really is powerful and moves the bow strongly. Problem is this unit after 3-4 short bursts of power drops the voltage to 10volt & runs very slow

My guess, The thruster takes loads of power , similar to cranking an engine.

So if the thruster batt is a deep cycle the plates get covered with gas , and the battery has little output. 10V

If the thruster batt is a start it will power the unit longer (more thin plates in a start batt) but still stops when the plates are covered with bubbles.10V

10 min after use either would show fairly fully charged as the heavy discharge was no where long enough to discharge the batt.

Solution more & BIGGER batts so the huge discharge rate of the thruster will gas the plate surface slower.

An extra 100A from an alt stuck on a noisemaker would also slow the arrival of 10V.
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Old 10-24-2013, 06:05 AM   #30
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Hi All, Well, the problem seems to be solved. I had a new 105 amp alternator installed to replace my old 80 amp unit, which appeared to be original to the engine. The thruster still drops the dash volt meter a couple of volts when engaged, but thruster runs strongly. The mechanic who installed the alternator (not the one from the boatyard doing the thruster install) also suggested that I have my battery switch on both when running. This will deliver power from 4 group 31s as opposed to the 2 I was using. I was always running on one bank or the other. I want to thank you all for the great advise. It truly is a wonderful community here. Well now it's day 4 of the trip south to Hilton Head SC for the winter, my first trip down the icw in 20 years.
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Old 10-24-2013, 12:05 PM   #31
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Hi All, The mechanic who installed the alternator (not the one from the boatyard doing the thruster install) also suggested that I have my battery switch on both when running. .
Be very careful with the "BOTH" switch. Turning the switch with the engine runnng can fry the alternator.
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Old 10-24-2013, 01:22 PM   #32
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A single on/off 'Combiner' switch is a better plan. Those 1-2-off-both switches have cause many-a-dead-battery in the boating world. Pull up to an anchorage and sit for a day or two with it on both and you'll be calling SeaTow for a jump.

Like this:
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Old 10-24-2013, 01:30 PM   #33
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A single on/off 'Combiner' switch is a better plan. Those 1-2-off-both switches have cause many-a-dead-battery in the boating world. Pull up to an anchorage and sit for a day or two with it on both and you'll be calling SeaTow for a jump. Like this:
Thanks for that Tom B and your post Tom Sunchaser. Those two posts cleared up a couple gremlins I've been trying to vet out recently.
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Old 10-24-2013, 02:14 PM   #34
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Hi All, Well, the problem seems to be solved. I had a new 105 amp alternator installed to replace my old 80 amp unit, which appeared to be original to the engine. The thruster still drops the dash volt meter a couple of volts when engaged, but thruster runs strongly. The mechanic who installed the alternator (not the one from the boatyard doing the thruster install) also suggested that I have my battery switch on both when running. This will deliver power from 4 group 31s as opposed to the 2 I was using. I was always running on one bank or the other. I want to thank you all for the great advise. It truly is a wonderful community here. Well now it's day 4 of the trip south to Hilton Head SC for the winter, my first trip down the icw in 20 years.
Your solution likely resides in you selecting BOTH and not the new alternator. I guess to nauseate you a little bit(after spending the money that you have), try turning that switch back to the way you had it and see if you suffer the same problems with the new alternator. Anyway, you are likely masking the real problem with just more battery/alternator power. But we can always use a bigger alternator so that was not money wasted....

Why were you running on anything other than both?

PS....Blue Seas makes some pretty good stuff to combine and isolate batteries for start/house purposes. Google them and read about them. If you do not understand it all, ask your marine electrician. They provide some good solutions if you feel the need to isolate banks while underway or at anchor
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Old 10-24-2013, 03:56 PM   #35
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A single on/off 'Combiner' switch is a better plan. ...
Like this?



(I normally have the parallel switch in the off position.)
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Old 10-25-2013, 05:46 AM   #36
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>Be very careful with the "BOTH" switch. Turning the switch with the engine runnng can fry the alternator.<

Switching from one battery bank to the other 1-2 or 2-1 is fine.

Switching to Both is fine.

The ONLY danger is a cheap or improperly wired wired switch that is turned to OFF with the alt charging.

Any of the better switches have a set of terminals that break the alt field, look at the back of the switch.

This is a break (the field ) before break (the batts) so there is zero danger.

On a crap switch turning the batts off on a running alt will require new diodes .

No danger with proper switching equipment.
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