I am rewiring some of the electrical in my O'Day 34 and want to know if its a problem to wire my alternator to a AB type battery switch in order to shut of the alternator when the batteries are full and I have to motor for a while. I disconnnected it at noticed the output of the alternator went up to about 23 Volts. Does any one know if this will damage the alternator if its is disconnected from the batteries?
Alternator Question?
- Thread starter simplicity
- Start date
- Status
No Need
Previous posters are both correct. Shutting off the alternator output with the engine running will blow the diodes in the alternator. The regulator will cut the output back to a float level when the batteries are fully up.
Previous posters are both correct. Shutting off the alternator output with the engine running will blow the diodes in the alternator. The regulator will cut the output back to a float level when the batteries are fully up.
If you disconnected the alternator from a battery while it was running I'm sure its not working correctly now.....common mistake people make is to disconnect the battery wire from the terminals.
While your engine is running test with a meter at the battery and you should have 13.7 or better then your alternator is OK
While your engine is running test with a meter at the battery and you should have 13.7 or better then your alternator is OK
Ouch..
Yes, it can definitely damage the alternator. As others have mentioned there is no need to disconnect the alternator from the batteries. We have hundreds of millions of vehicles world wide that never disconnect the alternator and the batteries do just fine..You will want to check your alternator out to be sure it is operational and many auto-parts stores will do this for free but you need to bring it to them. You can check it yourself with a AC/DC clamp DVM and a discharged bank. With the banks at or near dead you should see close to the full rating of the alternator in amp output. Hopefully the batteries were near full charge and putting out low output otherwise the diodes may be toast.
Good luck and let us know what you find.
Ok I will check the amp output. The boat had the alternator connected to two separate small isolators and then to each of the 2 batteries. I had measured the voltage at the battery and it was ready about 13 volts with the engine running and batteries slightly depleated. I had read that cheap isolators drop the voltage about .7 volts. Can anyone tell me if this is true, and if it is whats the sense in the isolators.And after all this what is the proper way to connect an alternator to 2 different batteries .
If you have diode based "isolators" they do indeed have about 0.7 v drop. The only way to overcome this is by using a regulator that can sense the battery directly. Most stock alternators are not set up for remote battery sensing and this normally requires an external regulator $$$.
That being said diode based isolators have gone the way of the Dinosaur and have been replaced by voltage sensitive combining relays, sometimes called ACR's (automatic combining relays) or devices like the Echo Charger or Balmar's Duo Charger. These devices automatically "combine" the banks when charging voltage is present and isolate them when the charging voltage disappears.
The Echo Charger bleeds off up to 15A of charge current to feed a reserve or starting bank but it does not technically "combine". It's a one-way device flowing FROM the house bank TO the reserve/start bank..
The best technology we have today for charging two banks from one source are ACR's or Echo Charger type devices. ACR's cost less up front but require larger wire and larger fuses making them darn close to the installed price of an Echo type charger.
Using a "dumb" regulator in conjunction with a diode isolator can cause chronic undercharging. At below 14 volts it may take days to get your banks to 100% not hours..
RANT ON
Common myth
Disconnecting the battery while the engine is on does not always (I've never had it happen in 50ish hot battery swaps) result in fried diodes, the regulator will do it's job and regulate the voltage below the breakdown voltage of the diodes. Your 23 volts while disconnected and engine running is just the regulator "seeing" a "battery" that seems to need charging badly as it "will not hold a voltage". so it bumps up the voltage to a respectable 23 volts AND HOLDS IT THERE.
IT DOES NOT LET THE ALTERNATOR "RUN WILD" AND PRODUCE 50+ VOLTS AS SOME FOLKS WOULD LEAD YOU TO BELIEVE.
Those folks all sell diode savers BTW so they need you to be scared so you can help put their kids through college.
The same crowd will tell you that the old is out (diode isolators) and the new is in (because we are still putting the kid through graduate school) so you need to buy a solenoid isolator...... I've seen the cycle which goes like this;
The best way to control your batteries is a 3-way so you can be in control all the time.
You don't want to mess with being in control all the time, you need an automatic system like diode isolation (and a combiner switch).
Those diodes isolators and switches we sold you last year have voltage drops in them and we certainly do not recommend that. What you need this year is an electromechanical isolator (and a new combiner switch cause the old one is dirty) solenoid.
Those electromechanical solenoids don't allow you to precisely control (you want to be in control don't you) your batteries and you really don't need a combiner switch if you just go with a 3-way switch.
Repeat ever 4 years,
This year we should see a return to 3-way switches BTW so the trendy among you will no doubt want to get yours now before they run out.
We live in a "you have to consume" society. EVERYTHING is dependent on you continuing to consume. There are no final solutions but you need to "keep current"
Rant off
There are three basic ways to set up a charging system on a single engine boat with single alternator.
Use a 3-way for house and start and connect the alternator output to the common on the 3-Way
Run the alternator output to isolation diodes (one for each bank) and put the voltage sense line on the regulator to the house bank + terminal. Then install a combiner switch so you can connect the start and house in emergencies.
Replace the diodes with solenoids. You can move the voltage sense line back to the alternator but you still need a combiner switch.
Each has its advantages. I’d go for least expensive which is leave your system alone if it ain’t broke. They all charge batteries fine (if properly used/installed)
Common myth
Disconnecting the battery while the engine is on does not always (I've never had it happen in 50ish hot battery swaps) result in fried diodes, the regulator will do it's job and regulate the voltage below the breakdown voltage of the diodes. Your 23 volts while disconnected and engine running is just the regulator "seeing" a "battery" that seems to need charging badly as it "will not hold a voltage". so it bumps up the voltage to a respectable 23 volts AND HOLDS IT THERE.
IT DOES NOT LET THE ALTERNATOR "RUN WILD" AND PRODUCE 50+ VOLTS AS SOME FOLKS WOULD LEAD YOU TO BELIEVE.
Those folks all sell diode savers BTW so they need you to be scared so you can help put their kids through college.
The same crowd will tell you that the old is out (diode isolators) and the new is in (because we are still putting the kid through graduate school) so you need to buy a solenoid isolator...... I've seen the cycle which goes like this;
The best way to control your batteries is a 3-way so you can be in control all the time.
You don't want to mess with being in control all the time, you need an automatic system like diode isolation (and a combiner switch).
Those diodes isolators and switches we sold you last year have voltage drops in them and we certainly do not recommend that. What you need this year is an electromechanical isolator (and a new combiner switch cause the old one is dirty) solenoid.
Those electromechanical solenoids don't allow you to precisely control (you want to be in control don't you) your batteries and you really don't need a combiner switch if you just go with a 3-way switch.
Repeat ever 4 years,
This year we should see a return to 3-way switches BTW so the trendy among you will no doubt want to get yours now before they run out.
We live in a "you have to consume" society. EVERYTHING is dependent on you continuing to consume. There are no final solutions but you need to "keep current"
Rant off
There are three basic ways to set up a charging system on a single engine boat with single alternator.
Use a 3-way for house and start and connect the alternator output to the common on the 3-Way
Run the alternator output to isolation diodes (one for each bank) and put the voltage sense line on the regulator to the house bank + terminal. Then install a combiner switch so you can connect the start and house in emergencies.
Replace the diodes with solenoids. You can move the voltage sense line back to the alternator but you still need a combiner switch.
Each has its advantages. I’d go for least expensive which is leave your system alone if it ain’t broke. They all charge batteries fine (if properly used/installed)
Bill,
"Common myth" try telling that to the many boaters who have blown their diodes by passing though off or disconnecting the load.. Many alternators do not have sufficient protection internally to sustain a disconnecting of the "load". I have seen Hitachi's, Delco's, Motorolla's, Mando's, Leece-Neville's, Balmar, Ample Power and others all suffer this fate. Balmar fully admits that theirs don't have any protection from disconnecting the load.. Some car alternators do, don't really know why but they do as the load is rarely if ever disconnected, but most marine alts, including Balmar's do not have this internal protection.
Having dealt with numerous blown diodes from passes through "OFF" I know quite well that this is not a "common myth". Does it happen every time no, but it certainly does happen. My alternator re-builder I'm sure would agree as he makes lots of money each summer from servicing alternators that have suffered blown diodes.
While it may not always happen it certainly can and does quite often when you disconnect the load from the alternator. I have an 55 amp Motorolla off a Perkins I need to drop off for re-build right now, or find a already re-built one, one that suffered a disconnected load and then stopped working when my customers 9 year old turned off the battery switch at the mooring, thinking she was helping to shut everything down.
Zap Stops & TSP's are ideally a band aid approach. Zap Stops are a ONE TIME device and the second time you pass through off you can still kill your alt because the Zap Stop sacrificed itself the first time. My 75 year old neighbors blew the diodes on their Yanmar alt multiple times even after installing a Zap Stop. The TSP from Balmar is slightly better in that a fuse blows, but, who is to know they blew the fuse? So, often, on the next pass through OFF the alternator still gets cooked. Most folks don't even know they passed through off or disconnected the load until the alternator is no longer working so how would they know to check the fuse on the TSP?
Interesting perspective but one I find rather odd as I have yet to see any marine electrician I know go backwards to diode isolators. There are some "fad" systems out there, that I see little benefit in, but there is nothing wrong with a properly wired 1/2/BOTH/OFF switch and I have never suggested a customer remove one.
As someone who had done this sort of thing for a long time I see a LOT MORE "consuming" from folks who set their systems up incorrectly. Large voltage drops from a diode isolator that was incorrectly installed leading to battery failures every season and a half and combined with an alt that only ever put out 13.8V to begin with is but one example. I see far fewer failures and "consuming" from those who take the time to do it well up front and longer battery life is the major benefit I see most often.
The cheapest way but one that can leave you exposed to "consuming" failures like blown diodes.
This can get $$/"consuming" with an alt that has an internal regulator and you need to have a shop re-wire it for external "sense". Not all internally regulated alts can sense at the battery without modification.
If you are using simple "key on" or "switch on" basic solenoid you should not need an additional combining switch if the rating of the solenoid is sufficient because all you need to do to combine is turn the key on or flip the solenoid switch closed..
There are quite a few other alternatives and there are many ways to wire a single alt to two battery banks quite reasonably and protect the diodes at the same time.
Thanks for all that technical input. I am still confused a bit and would like to install the simplest and most functional way. So how about this. ( 1) Install the alternator output thru an ampmeter then directly to the battery switch common terminal. I know this will require me to keep track of charging. Or ( 2 ) from ampmeter to another battery AB switch (used solely for charging) then to the individual batteries,with this method I can have the house batteries supplying the ships load, but still charging the start battery. This seems a better way to me. Would there be any problems with this second method.
The most simple way is an ammeter shunt on the house bank negative and an ammeter display. The Victron BMV-600 battery monitor does all that and much more for only $158.00. I have seen battery monitors pay for them selves numerous times in longer battery life.
A very simple and easy system is to run your alt output direct to the house bank then wire in a Blue Seas ACR to charge the start battery automatically. By doing this you no longer need to do anything with the 1/2/ALL/OFF switch other than flip it to the house bank when you get to the boat and turn it off when you leave.
The cheapest way is to run the alt the batt switch and rely on your memory to switch if off ALL when not charging.
I'm sure Stu will chime in with some links to previous discussions on this subject.
Here's a few:
Wiring & Installing A Battery Monitor
Battery Bank Sizing What Does It Mean??
Musings Regarding External Regulation
Batteries - Reserve Capacity vs. Amp Hours
Not if you are good about being careful with your 1/ALL/2/OFF switch. If you ever decided to ad an Echo Charger or Balmar Duo Charger to charge the start bank then you would need to re-direct it to the house bank but for general charging no need of you are careful.
Many boaters are not careful, are forgetful and choose to use an automated system to help deal with charging the second bank without the need to ever flip the switch.
Hey MS
All good comments to my rant. Thanks for listening. I've been messing around in boats for some time now and have never had nor do I know anyone who has had a blown diode in an alternator. Perhaps you should consider that ANY reason for the alternator not working correctly is good enough for most folks to replace it. No doubt it happens but my experience is that lots of alternators are replaced because of loose/corroded connections. Course when you replace those in the auto industry you also ALWAYS clean the cables at the alt and bat. And now you know why we replaced a lot of perfectly good alternators. I can say they where good because while trying to rebuild them there was nothing wrong with them.
I have absolutely no confidence in mechanics. They are all just parts replaces and could not diagnose their way out of a wet paper sack.
All good comments to my rant. Thanks for listening. I've been messing around in boats for some time now and have never had nor do I know anyone who has had a blown diode in an alternator. Perhaps you should consider that ANY reason for the alternator not working correctly is good enough for most folks to replace it. No doubt it happens but my experience is that lots of alternators are replaced because of loose/corroded connections. Course when you replace those in the auto industry you also ALWAYS clean the cables at the alt and bat. And now you know why we replaced a lot of perfectly good alternators. I can say they where good because while trying to rebuild them there was nothing wrong with them.
I have absolutely no confidence in mechanics. They are all just parts replaces and could not diagnose their way out of a wet paper sack.
Bill,
All the ones I mentioned were blown diodes and most rebuilt not replaced. Some were upgraded but the old alt still re-built for spare. When your alt is working fine one minute then you flip the switch to off and then the alt is no longer working it is fairly obvious what happened. My customer with the Cape Dory knew immediately when her daughter shut the switch off what had happened. She flipped it back on but it was too late. Keep in mind that at least two companies, as you stated, have made good money off the fact that disconnecting the load to the alt with the engine running can cause the diodes to go poof. There are obviously a lot of boaters who have experienced this, enough to develop a product and get West Marine to stock it.
Also of note is the fact that many battery switch makers install a "Field Disconnect" (AFD) terminal on the battery switch so that an owner can cut the field voltage slightly before the switch passes through OFF. The reason for this feature, as you know, is to.....prevent frying the rectifying diodes. Blue Seas, Perko & Guest all offer an AFD switch.
Having seen piles of switches with field disconnects, and only perhaps two being used, my guess is that most folks have no clue what it is or how to access the field wire to connect it properly? They are much easier to access with an external regulator.Perhaps we see more of them blown up here because the vast majority of boats in Maine are on moorings and completely shut off when the owners are leaving. I would say the most prevalent time I hear about them being blown is when arriving back at the mooring and closing up the boat which usually involves disconnecting the batt switch.
I always questioned a run away diesel until I experienced it myself 80 miles of the NJ coast in a 65 foot sport fishing boat but it does not mean they don't or didn't happen..
Here is a link to some more links that are relevant and answers Stephan's qustion, too: http://c34.org/bbs/index.php/topic,5977.0.html
- Status