Electrical & Boats 101: How does it work?

[pred02]

Ok, so this may be a very rudimentary question but this is going to be our first boat with an electrical system. The boat in question is going to be the Sea Ray 240DA.

There is a number of electrical devices, such as lights, starter, fridge, radio, etc.

1. Shore power - I presume when plugged into shore power all electrical is going to work and no batteries are going to be used.

2. Engine running - when the engine running, is power supplied by the batteries or by the engine? Are the batteries being recharged when the boat is running? If so how long does it take the batteries to fully recharge? Or does shore power recharge the batteries?

3. Engine not running / no shore power - I presume that then the batteries are running. If we have the fridge on and the radio, how long can they last with the batteries on?

Batteries - as with all batteries I presume these run out and need to be replaced. Does a mechanic need to replace them or can they simply be swapped out? If so where can we get extra batteries (we are shipping the boat overseas)? Can we purchase them online? I presume these batteries can also be bought in Europe?

Thanks for the feedback!

 

[tdappleman]

1. Shore power - I presume when plugged into shore power all electrical is going to work and no batteries are going to be used.

Devices like lights, radios, etc are 12volt and will run from the batteries. The fridge (if dual voltage), AC, outlets will run directly from the electrical source when plugged in. You will want to run your AC converter/charger when plugged in which will provide charging capabilities to your batteries. Some converters will provide a 12volt source so they will power your devices + charge your batteries.

2. Engine running - when the engine running, is power supplied by the batteries or by the engine? Are the batteries being recharged when the boat is running? If so how long does it take the batteries to fully recharge? Or does shore power recharge the batteries?

When the engine is running it provides power from the alternator like your car. It will provide power for your 12 volt accessories. If the draw is higher than the output of the alternator then it will draw power from the battery to compensate. Not an ideal situation - and unlikely unless you are running everything at one time and have a high powered stereo amp or something similar. If the draw is lower than the output it will then provide some charging capability to your battery. Shore power will charge your battery as mentioned above.

3. Engine not running / no shore power - I presume that then the batteries are running. If we have the fridge on and the radio, how long can they last with the batteries on?

Depends on what type of battery and how many you have. Some deep cycles are meant to run the radio, etc for quite a few hours but it really depends on the rate of consumption. I have 3 batteries on mine (group 27 deep cycle) and can run the fridge, lights and radio for a few days. I forgot to turn on my shore power one weekend when at home and my fridge ran the entire week (6 days) and the engines started right up. Keep your battery maintained - water level correct and fully charged for the best performance.

Batteries - as with all batteries I presume these run out and need to be replaced. Does a mechanic need to replace them or can they simply be swapped out? If so where can we get extra batteries (we are shipping the boat overseas)? Can we purchase them online? I presume these batteries can also be bought in Europe?

They can be swapped out - you can get marine batteries almost anywhere. A lot of threads on here about which type to get. AGM batteries seem to get the best ratings here and will cost a bit more but seem to be the best bet. If you have multiple batteries in a bank make sure they are the same type and same age for the best performance. I'd also assume you could purchase them in Europe and then you'd have someone local to deal with in case of warranty problems.

 

[pred02]

. If the draw is lower than the output it will then provide some charging capability to your battery. Shore power will charge your battery as mentioned above.

Thank you for your detailed response. Just to sum up, 12V devices can run when the boat engine is running (i.e. dual voltage fridge) and the batteries are best charged when using shore power. The problem is that we may not have the boat in marina therefore shore power may not be available to charge batteries. I understand not running the fridge etc but we need the starter/lights. Do you think we can be ok without shore power on this size boat?

Thanks!

 

[Alegria]

Hi welcome...

I can only give you feedback from my experience. But on our old boat (280 Sundancer) we did not have a battery charger/AC Convertor. So I was entirely dependent on running the motors to charge the batteries. It was OK as long as I ran the boat and charged the batteries. If you are only going to run for a little while, an hour or so and then anchor out you might not get the run time to charge the batteries and may find yourself depleting them quicker. I did not have problems as I ran the boat most of the time so the batteries were OK. Also you may want to look at a solar charging option if you are going to keep it in the water with no shore power...

Also if you have 2 batteries and a switch. The switch will be labeled 1,2, both. You can run on either battery and charge/discharge either one. Or run with the 'both' setting to charge the batteries, then when you anchor, switch to 1 or 2 to keep one battery as a reserve to start.

I don't know if it applies but I was always under the impression not to switch the switch while the motor was running in fear of damaging the alternator... Do a search as I know there is a big thread around with lots of comments on it and I forget what the final outcome was of it!!

 

[tdappleman]

Thank you for your detailed response. Just to sum up, 12V devices can run when the boat engine is running (i.e. dual voltage fridge) and the batteries are best charged when using shore power. The problem is that we may not have the boat in marina therefore shore power may not be available to charge batteries. I understand not running the fridge etc but we need the starter/lights. Do you think we can be ok without shore power on this size boat?

Thanks!

Will you ever be able to plug in? Will this be trailered? I'd recommend plugging into electric when possible to keep the batteries topped off. The engine alternators are limited to how much output they have and if you are on the hook overnight and then have a relatively short run back to the dock or trailer then don't expect them to fully charge the batteries.

The suggestion of using the battery switch is a good one - running on one battery at a time will ensure you have a charged battery to start the motor and the alternator will charge a single battery faster than trying to charge a bank of batteries.

Do NOT turn the battery switch to off or switch from bank 1 or 2 while the engine is running - it will immediately damage the alternator. You most likely have a warning label near the switch as well.

 

[pred02]

Will you ever be able to plug in? Will this be trailered?

The boat will not be regularly trailered - only from the dry marina and back from the beginning and end of the season. The problem is that there are no berths in the little marina on our island (and berths are very expensive - 40 euro/night). We will most likely have a private berth in a little cove accessible with a dingy but no electrical plug in power. Plug in will be there for overnight trips on other islands in marinas.

Maybe worthwhile bringing a portable generator, like the Honda EU2000i to charge while anchored and swimming away? Thanks

 

[LifeisGood]

You may want to search the forum for the risks associated with a portable generator. There is a lot of valuable information and opinions.

 

[Sundancer]

Check your battery switch, if it is a "make before break" switch you can switch it while the engine is running. I do so routinely with a Perko on both of our boats. DON'T switch it to off accidentally or you will torch your alternator in a heart beat. We had our 250 DA for 4 years before we added a charger. We didn't run a refrigerator however! We just ran the lights and the water pump. Ice was our friend!