# help me -control engineering

Discussion in 'OnBoard Electronics & Controls' started by jollyricard, Mar 10, 2012.

1. Joined: Jul 2009
Posts: 73
Likes: 0, Points: 0, Legacy Rep: 10
Location: italy

### jollyricardJunior Member

Dear ALL,

My name is riccardo, I have received question regarding some procedure on board of ships . I don't understand what to do for Prepare for starting, paralleling and change-over of alternators or generator.
Moreover what is reverse power? What does it mean ?

B/R

2. Joined: Aug 2002
Posts: 16,230
Likes: 1,366, Points: 123, Legacy Rep: 2031
Location: Milwaukee, WI

### gonzoSenior Member

What is your background in electronics?
By reverse power, do you mean power to reverse the vessel?

3. ### Submarine TomPrevious Member

Or do you mean reverse polarity?

-Tom

4. Joined: Mar 2012
Posts: 9
Likes: 4, Points: 0, Legacy Rep: 51
Location: Stuart FL

### gdougGD

Some boats with larger engines have parallel switches. A parrallel switch completes a circuit that couples multiple batteries so that you have more power than 1 battery.
Normally each engine has it's own starting battery. However starting engines draws a lot of power. For this reason circuits are created that couple each starting battery so that you have more power available.

A parallel switch parallels the starting batteries. When you parallel two batteries you connect them in such away that you keep the same voltage as 1, but increase the amperage therefore increasing power. Power in watts = Voltage X current (in amps).
For example if you parallel two 24V 80 amp batteries the resulting voltage is 24V, but the resulting amperage is 160. This gives you twice the power.
You parrallel batteries when starting to give you twice the starting power.
It's just a safety to protect each individual battery from getting over drawn during start up. Over drawing some batteries can perminately damage them.

About reverse power. I personally have never heard this term. I'm not sure what you're referring to, but if you explain I may be able to help you out.
Cheers,

5. Joined: Mar 2012
Posts: 9
Likes: 4, Points: 0, Legacy Rep: 51
Location: Stuart FL

### gdougGD

Generators are combustion engines that essentially have an electric motor arts Ted to them. And electric motor uses electricity to power copper windings which turn magnets. The magnets are then usually fastened to a shaft (simple example). So when you apply a volage to an electric motor you power the windings which move magnets which move a shaft. Transversly if you use a shaft to turn magnets in windings you will create a electricity. This is how a generator works. The shaft of a combustion engine turns an electric motor creating a voltage.

Generators on boats have 2 purposes. 1 to charge batteries, 2 to power electronics. The only way they would be needed for starting is if your starting batteries are drawn and need to be charge. BUT! Starting batteries aren't usually hooked up to a generator. You shouldn't need to start a generator to start the boat.

Unfortunately every boat is different. It's not safe to run or work on a boat if you don't understand the electrical system. You need to find wire diagrams for the boat and have a Marine electrician review them with you.

6. Joined: Nov 2007
Posts: 2,933
Likes: 66, Points: 48, Legacy Rep: 719
Location: Melbourne/Singapore/Italy

he will mean one generator powering another, common problem with older systems when lightly loaded and you are trying to get another online/parallel it

7. Joined: Aug 2002
Posts: 16,230
Likes: 1,366, Points: 123, Legacy Rep: 2031
Location: Milwaukee, WI

### gonzoSenior Member

If they are A/C the cycles need to be synchronized

8. Joined: Jul 2009
Posts: 73
Likes: 0, Points: 0, Legacy Rep: 10
Location: italy

### jollyricardJunior Member

ok thanks but I don't understand the term "reverse power" used for diesel generator on board ships.

9. Joined: Aug 2002
Posts: 16,230
Likes: 1,366, Points: 123, Legacy Rep: 2031
Location: Milwaukee, WI

### gonzoSenior Member

There isn't such a thing. Are you translating from Italian? There may be a misunderstanding due to that.

10. Joined: Dec 2008
Posts: 4,862
Likes: 115, Points: 0, Legacy Rep: 1180
Location: spain

### michael pierzgaSenior Member

Are you mistaking REVERSE for BACKUP ?

Backup or manytimes labeled STANDBY typically means that DC to AC inverters take over when the generator or shorepower shuts down

11. Joined: Nov 2007
Posts: 2,933
Likes: 66, Points: 48, Legacy Rep: 719
Location: Melbourne/Singapore/Italy

geez sometimes you guys...

http://www05.abb.com/global/scot/scot296.nsf/veritydisplay/c1256d32004634bac1256e0f006bf54f/\$file/1mrk509042-ben_en_reverse_power_relay_and_protection_assemblies_rxppk_2h__rappk.pdf

reverse power means one gen set it motoring another, its a common term and problem on large gen sets
The vessel will have control circuits to trip the gen set off line to prevent it being motored as above

12. Joined: Dec 2008
Posts: 4,862
Likes: 115, Points: 0, Legacy Rep: 1180
Location: spain

### michael pierzgaSenior Member

I have never used generators in parallel that have a user controled circuit labeled REVERSE. It is protected, but this protection is in the background.

13. Joined: Nov 2007
Posts: 2,933
Likes: 66, Points: 48, Legacy Rep: 719
Location: Melbourne/Singapore/Italy

it isnt a user controlled circuit and it usually isnt on gen sets of up to a couple of hundred kw

14. Joined: Dec 2008
Posts: 4,862
Likes: 115, Points: 0, Legacy Rep: 1180
Location: spain

### michael pierzgaSenior Member

I trust what you say. Load distribution on the yacht size gen sets Ive used is automatic.

15. Joined: Nov 2007
Posts: 2,933
Likes: 66, Points: 48, Legacy Rep: 719
Location: Melbourne/Singapore/Italy