What is the correct procedure for shutting off the MD 7A? After killing the engine by pulling the shut off cable, I immediately return the cable to its original position and then remove the key. Is this correct? Should I wait for any period of time? Thanks.
dmetznic@ix.netcom.com
Volvo MD 7A: shutting off
Moderator: Jim Walsh
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D. Stump, Hanalei
Re: Volvo MD 7A: shutting off
Don,
I just checked with the skipper of Dolphin III, a CD-30 with the MD7A. Your procedure IS correct...idle her down, pull the decompression lever, and shut off the key. No waiting necessary. DON'T ever shut off the key first - you would blow the diodes in the alternator if you do!
The Universal 18 in Hanalei is shut off the same way.
Dave Stump
Captain Commanding
s/v Hanalei CD-30
I just checked with the skipper of Dolphin III, a CD-30 with the MD7A. Your procedure IS correct...idle her down, pull the decompression lever, and shut off the key. No waiting necessary. DON'T ever shut off the key first - you would blow the diodes in the alternator if you do!
The Universal 18 in Hanalei is shut off the same way.
Dave Stump
Captain Commanding
s/v Hanalei CD-30
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Larry DeMers
Re: Volvo MD 7A: shutting off
Don,
The procedure for shutting down is correct as you are doing it..but I wanted to correct some mistaken impression given earlier by another poster. Shutting off the key switch on the starter panel *will not* blow the alternator diodes. It has nothing to do with the alternator or it's diodes..it just applies power to the alarm circuitry (idiot lights and sensors)and starter solenoid circuit. The switch that you most definitely do not want to shut off while the engine is running is the "1-2-both-off" switch on the breaker panel in side the boat. This action removes the loads from the alternator, cutting off the voltage reference that the alternator was trying to raise through charging (ie: it's sensed voltage goes to zero, which to the alternator then seems like a battery in bad need of a charge, so it ramps up the charge rate). The result is that the voltage spikes out at well over 100VDC, and those diodes are spec'd. at something considerably less than this. The end result is that the diodes get popped, and you will have a 2-3 hour job ahead of you changing out the diode packs (2). So don't switch the *battery switch*.
Also, the lever that you pull to shut down the engine is that black handle on the starter panel. This IS NOT the compression release lever (which is on the engine top..right side facing the engine). That black lever is actually a fuel cut-off lever. Try turning the engine over with it pulled vs. not pulled. If that was a decompression lever, the rpm's should increase with no compression..it doesn't.
Cheers,
Larry DeMers
s/v DeLaMer
Cape Dory 30
demers@sgi.com
The procedure for shutting down is correct as you are doing it..but I wanted to correct some mistaken impression given earlier by another poster. Shutting off the key switch on the starter panel *will not* blow the alternator diodes. It has nothing to do with the alternator or it's diodes..it just applies power to the alarm circuitry (idiot lights and sensors)and starter solenoid circuit. The switch that you most definitely do not want to shut off while the engine is running is the "1-2-both-off" switch on the breaker panel in side the boat. This action removes the loads from the alternator, cutting off the voltage reference that the alternator was trying to raise through charging (ie: it's sensed voltage goes to zero, which to the alternator then seems like a battery in bad need of a charge, so it ramps up the charge rate). The result is that the voltage spikes out at well over 100VDC, and those diodes are spec'd. at something considerably less than this. The end result is that the diodes get popped, and you will have a 2-3 hour job ahead of you changing out the diode packs (2). So don't switch the *battery switch*.
Also, the lever that you pull to shut down the engine is that black handle on the starter panel. This IS NOT the compression release lever (which is on the engine top..right side facing the engine). That black lever is actually a fuel cut-off lever. Try turning the engine over with it pulled vs. not pulled. If that was a decompression lever, the rpm's should increase with no compression..it doesn't.
Cheers,
Larry DeMers
s/v DeLaMer
Cape Dory 30
D. Stump, Hanalei wrote: Don,
I just checked with the skipper of Dolphin III, a CD-30 with the MD7A. Your procedure IS correct...idle her down, pull the decompression lever, and shut off the key. No waiting necessary. DON'T ever shut off the key first - you would blow the diodes in the alternator if you do!
The Universal 18 in Hanalei is shut off the same way.
Dave Stump
Captain Commanding
s/v Hanalei CD-30
demers@sgi.com
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D. Stump, Hanalei
Re: Volvo MD 7A: shutting off
Larry,
Now I"m confused. I could swear that the manual for the Universal 18 says "don't turn OFF the key while the engine is running"! I'll check the manual tomorrow to make sure. I do agree with you about the battery switch, turn that to off and you will "high side" the diodes! But, like I said, I think the manual also says don't turn off the panel switch. I'll let ya know what I find out.
Dave
Hanalei
P.S. Weather this weekend is forecast as 80 degrees, 10 - 15 knot NNW winds, 2-3 foot seas, bright sunny skies on Long Island Sound. I can't wait!
Now I"m confused. I could swear that the manual for the Universal 18 says "don't turn OFF the key while the engine is running"! I'll check the manual tomorrow to make sure. I do agree with you about the battery switch, turn that to off and you will "high side" the diodes! But, like I said, I think the manual also says don't turn off the panel switch. I'll let ya know what I find out.
Dave
Hanalei
P.S. Weather this weekend is forecast as 80 degrees, 10 - 15 knot NNW winds, 2-3 foot seas, bright sunny skies on Long Island Sound. I can't wait!
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Ryan Turner
But can you switch from 1 to 2 or to Both?
I've always heard not to switch to "off" while the engine is running but can you switch from "1" to "2" or to "both" while the engine is running? For instance, after spending a night or two at anchor my house batteries are low. I then switch to the other bank for starting. Then I'd like to switch back to the house bank in order to charge them. Or maybe I'd like to charge both banks at once so I'd like to switch to "both". Does anyone know if this is OK?
Ryan Turner
s/v Zenobia
CD33 hull no. 100
Oriental, NC
PS -- great forecast for the Pamlico Sound this weekend too. Can't wait!
rdtec@aol.com
Ryan Turner
s/v Zenobia
CD33 hull no. 100
Oriental, NC
PS -- great forecast for the Pamlico Sound this weekend too. Can't wait!
rdtec@aol.com
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Russell
Depends on the switch ..
The question is how the switch functions in the transition between "1", "2", and "both". Some switches give an open circuit for some of the movement, so that when you move the switch from "1" to "both" (for example), the alternator sees battery 1, then off (at some position between "1" and "both"), then both batteries. This presents a danger of blowing the diodes as if you had moved through the "off" position!
Other switches are designed to present at least one battery to the alternator for the full range from "1" through "both" to "2".
Switches are only digital in theory. In reality, they are analog devices.
Other switches are designed to present at least one battery to the alternator for the full range from "1" through "both" to "2".
Switches are only digital in theory. In reality, they are analog devices.
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Al Levesque
Re: But can you switch from 1 to 2 or to Both?
Our switch is a "make before break" type, meaning that switching from 1 to both and both to 2 keeps a load on during switching. Our CD33 is hull 94 and probably has the same switch that you do. We often switch while running with no adverse effects. On the other hand, some experienced boaters recommend not switching because of the possibility of switch malfunction that allows momentary opening of the circuit.
In practice, our switch causes us to join the batteries when going from one to the other so we usually start on both and leave it there when running the engine so that both get charged.
Al
albert.levesque@cwixmail.com
In practice, our switch causes us to join the batteries when going from one to the other so we usually start on both and leave it there when running the engine so that both get charged.
Al
albert.levesque@cwixmail.com
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Neil Gordon
Re: But can you switch from 1 to 2 or to Both?
>>On the other hand, some experienced boaters recommend not switching because of the possibility of switch malfunction that allows momentary opening of the circuit.<<
Even with protected switches, best practice is to follow the rule of don't touch the switch while the engine is running. Given the slightest chance, your brother-in-law will cause serious damage to your boat!!! <g>
>>... we usually start on both and leave it there when running the engine so that both get charged.<<
That's my practice, too. Use both to start and leave it that way for charging... then when the motor is shut down, switch to odd or even depending on the day of the week.
Regards, Neil
s/v LIQUIDITY
Cape Dory 28 #167
neil@nrgordon.com
Even with protected switches, best practice is to follow the rule of don't touch the switch while the engine is running. Given the slightest chance, your brother-in-law will cause serious damage to your boat!!! <g>
>>... we usually start on both and leave it there when running the engine so that both get charged.<<
That's my practice, too. Use both to start and leave it that way for charging... then when the motor is shut down, switch to odd or even depending on the day of the week.
Regards, Neil
s/v LIQUIDITY
Cape Dory 28 #167
neil@nrgordon.com
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Ed Haley
Re: But can you switch from 1 to 2 or to Both?
I agree with Neil. Whether the switch was designed to "make before break" or not, it eliminates the risk of frying the diodes if the switch is never changed while the engine is running. My switch (which is supposedly "safe") sometimes is and sometimes isn't. I can tell contact is not made before breaking because when I switch batteries (engine not running) the change resets my radio and my autopilot sometimes. Sometimes it does and sometimes it doesn't. I won't take a chance with my alternator. I religiously think twice and sometimes three times before changing the battery switch.
eghaley@dreamscape.com
eghaley@dreamscape.com
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Larry DeMers
Re: Sure..but don't do it!!
Well guys,
My Cd30 #283 (1983) has a make-before-break switch, and I was so darn cocky sure that I could go to any position except off that I tried it one weekend..and spent the next weekend rebuilding that damn alternator. What a dumb way to waste a good weekend and around $35.00. I think what happens is that while there may be a switch closure (there is on mine according to my Fluke multimeter), the loads change momentarily, and that is enough to let the alternator run into the high voltage area, which is what pops those diodes.
Interestingly enough, the boat came with this neat little brass plaque that says in english and swedish...don't switch the batteries with the engine running -(unless you are bored and want a weekends work).
Cheers!
Larry DeMers
s/v DeLaMer
Cape Dory 30
demers@sgi.com
My Cd30 #283 (1983) has a make-before-break switch, and I was so darn cocky sure that I could go to any position except off that I tried it one weekend..and spent the next weekend rebuilding that damn alternator. What a dumb way to waste a good weekend and around $35.00. I think what happens is that while there may be a switch closure (there is on mine according to my Fluke multimeter), the loads change momentarily, and that is enough to let the alternator run into the high voltage area, which is what pops those diodes.
Interestingly enough, the boat came with this neat little brass plaque that says in english and swedish...don't switch the batteries with the engine running -(unless you are bored and want a weekends work).
Cheers!
Larry DeMers
s/v DeLaMer
Cape Dory 30
Ed Haley wrote: I agree with Neil. Whether the switch was designed to "make before break" or not, it eliminates the risk of frying the diodes if the switch is never changed while the engine is running. My switch (which is supposedly "safe") sometimes is and sometimes isn't. I can tell contact is not made before breaking because when I switch batteries (engine not running) the change resets my radio and my autopilot sometimes. Sometimes it does and sometimes it doesn't. I won't take a chance with my alternator. I religiously think twice and sometimes three times before changing the battery switch.
demers@sgi.com