Will I Damage My Alternator if I Switch Batteries While the Engine Is Running?

[@romeowhiskey1146]

Jeff: Thanks for this ONGOING series. If every sailor watched ALL of them...WOW...we'd all be just a little bit smarter.

[@PacificYachtSystems]

Most welcome! We are glad to do these videos to empower fellow boaters to stay safe out there on the water.

[@davidncw4613]

Lots of good info in these vids. An absolute library is available at their web site. I have to think a company that will offer this much info for free will be a hero with customer service. These guys will my preferred contractor with the boat I will retire on. I want this kind of service available with their system design on record if I am broke down.

[@PacificYachtSystems]

Really appreciate this feedback!

[@shadygrovesailing1157]

Awesome Topic New boat owner !, I didn’t know that you would fry your Alternator .. switching to Off while running or Charging..

[@PacificYachtSystems]

Welcome to boat ownership! Glad you caught this video in time. Thanks for watching!

[@kimhall4310]

I have an old boat with a wiring nightmare. I have been trying to run down a problem with my alarm/ light that has been going off more frequently for some time. In the process I found a wire on the alternator that has become disconnected. I have no idea which post this wire came off of. There are two posts on the alternator. One is marked B+ the other is marked R. The B+ goes to the starter and the other post appears to have a wire going to the tachometers. The unattached wire has power when the key is on and I have traced to a wire bundle that comes off after the key. What is this wire for and which of the alternator taps should it be connected to? If it were connected to the wrong post would it blow the diode in the alternator?

[@PacificYachtSystems]

Hi Kim, you seem to be on the right track with your detective skills. Based on your description, sounds like the ign wire from the engine key seems to be disconnected at the alternator. Since there are so many variations of alternator wiring, suggest you look online at your exact alternator model and find the post where the ign wire should be connected.

[@ackack612]

......whoa doggies, a PHENOMENAL question! You're the best, Jeff.

[@PacificYachtSystems]

Thanks David, glad you found interesting.

[@todddunn945]

The easy solution is to install an automatic charging relay (ACR) between the two battery banks. An ACR will electrically connect the two battery banks when the engine is running and the battery voltage goes above the threshold voltage of the ACR (typically 13 volts or so) and disconnect the two battery banks when the engine is off and voltage drops below about 12.75 volts. That way you always charge both battery banks when the engine is running (or something like solar drives one battery bank above 13V. You still may want a 1-2-both switch so you can start from both banks if the normal start battery is weak. Also some old battery switches break the circuit when switching from one bank to the other. Newer switches have what are called make before break wiring so the make the connection to the second battery bank before disconnecting the first battery bank - as long as you don't go through off as mentioned in the video.

[@alvarogazzolo8884]

Hi Jeff, my alternator is overheating. What are the possible causes, apart from the alternator being faulty?

[@frankareizaga1293]

Jeff I wonder, because I have 2 engines and of course 2 alternators. How would this effect it. Also only 2 battery banks.

[@BreakingWavesSailing]

Thanks Jeff

[@PacificYachtSystems]

Your welcome.

[@donniejohnston4114]

Great question and great answer 👍 keep up the good work

[@PacificYachtSystems]

Thanks for the support!

[@samersarouphim6670]

Hi, i really love these videos and i have a question. Does running the boat engine while the electrical marine charger is on might damage the alternator?

[@RR-or5ip]

This series is awesome! Thank you!

[@PacificYachtSystems]

Glad you enjoy it!

[@RR-or5ip]

@@PacificYachtSystems I have learned so much and literally watch everyone. I live in Japan and finding "Good" techs is damn near impossible. Your channel has helped out so much. THANK YOU!!!

[@benoitmaisonneuve8100]

Following your answer , can I really charge both batteries at the same time ? I thought it would be best to charge them one at the time , that the alternator would stop charging when the first battery would be full. Great serie Jeff !

[@PacificYachtSystems]

Hi Benoit, yep you can definitely charge both batteries at the same time.

[@robertschulke1596]

Depends on your batteries, alternator, v-belts, engine. Look into your battery bank’s charge acceptance rate vs your alternator. An old 45 amp alternator with a single v belt cannot feed an 800 amp hour battery bank without risk of overheating, frying the belt, etc. look into quality external regulators like Balmar.

[@sailingdevonscoast]

Can I ask what the difference is between these older style battery switches (which I have), and the dual bank control switches (which i am thinking of changing to)?

[@PacificYachtSystems]

Because difference, is that house and engine loads are separate, meaning engine battery powers engine/starter and house battery does all other loads. With one turn of the switch, both battery banks are connected to their separated loads only.

[@billhanna8838]

Would a battery switch with just B1 & B2 no off mark be OK to go from 1 to 2 while running ?

[@PacificYachtSystems]

Yep, as long as you don't disconnect the alternator from the battery while the alternator is outputting.

[@tao4409]

A switch with field disconnect contacts, apparently prevents this situation by providing a safe path to ground. Never tried one, but I've seen them. Yes, I know, someone previously mentioned this. Thumbs up, keel down. :)

[@PacificYachtSystems]

Good one, although I've never seen this implemented .

[@alrobertson1432]

​@@PacificYachtSystems About 20 Years ago I re-wired a boat. It had the classic Red 1 2 Both Off config. On the back it also had two small posts that were what I assume are called Field Disconnect Contacts. They would break contact before the main switch did, and I'm pretty sure I just ran the field circuit for the alternator directly through that switch. Nobody had ever heard of this then, and it seems few people know about it now. It's such a simple solution to prevent an easy, and expensive, mistake to occur.

[@jackbarnes694]

I need a new battery switch! Thanks for the video.

[@PacificYachtSystems]

Glad to help Jack.

[@romeowhiskey1146]

Jeff...suggestion for ALL TIME BEST video: "10 things EVERY boater should KNOW and shouldn't DO

[@PacificYachtSystems]

Great suggestion. Thanks for watching our videos!

[@dannyjensen4954]

Great video.

[@PacificYachtSystems]

Glad you enjoyed it

[@javierbetancourt9388]

💯

[@PacificYachtSystems]

Thanks

[@xs10z]

0:11 "Jeb... Jeff". Who misprounounces their OWN NAME lol?

[@PacificYachtSystems]

I've add language issues forever... friends and family keep laughing about it... in a nice way of course.

[@ThinKkBIGG]

Jeff Coté is a French name. Do you speak French or come from Quebec? By the way, thank you for your videos!

[@ThinKkBIGG]

Pas de réponse Jeff 😉!!!

[@PacificYachtSystems]

Yep, mom is French Canadian and grew up in eastern Quebec. Dad is bilingual and spend is whole career working in the merchant marine company, grew up hearing about boats most days of my childhood and found it fascinating.

[@ThinKkBIGG]

@@PacificYachtSystems Super! I have several members of my family from Quebec who live in Vancouver. You haven't learned French? Au plaisir!

[@daveengstrom9250]

When you say "blow up" the alternator, are you talking "disabling, or malfunction? Or are you literally saying an explosion?

[@PacificYachtSystems]

Ahh good question, well in most cases it stops working in some rare circumstances it's like a mini explosion blew or melted a part of the alternator away.

[@scruff7559]

Engineering 101 do not enable the system or the user to harm the system or themselves.

[@PacificYachtSystems]

Well said Liam!

[@scruff7559]

Thinking about it. If one must fit that switch type for reasons I'll never understand then the alternator ought to be hardwired to the engine battery. By your logic, it would have not cost much more and be more useful to have 2 alternators outtov the gates, one per battery.