Stereo/Electrical Question - New 1979 30' Hunter Owner

[Brianthomas]

Hi All,

I recently purchased a '79 30ft Hunter from my grandfather who no longer has the capacity to sail. I have experience with boats in general but limited sailing knowledge - I have been trying to bring myself up to speed with multiple resources.

I have a laundry list of projects, but currently working to replace the original stereo head unit which is dead. I was looking at two different options - either running a new head unit and installing two 6.5 speakers, or using a powered "boombox" like the altec lansing linked here http://www.alteclansing.com/ae/us/i...imt810/&bklist=icat,3,shop,ipodiphonespeakers.

After pulling out the corroded existing head unit, I realized that rewiring the new head unit may be a bit over my head. The altec lansing boombox sounds great and is a simple solution.

I wanted to see if there is any drawback to using the boombox which is just plugged into an outlet. I have been trying to get a grasp on AC vs DC and the impact on battery draw. The boat runs off shore power in the harbor, but I am wondering if the power drain will be an issue away from the dock.

Lastly, if I go the head unit route, I would have to run power off of the boat batteries to power the unit on rather than just running AC and outlet power off the shore, correct? Supposing i have the battery charger switched on, this shouldn't be an issue correct?

Apologies for my ignorance, any help would be greatly appreciated.

 

[Ed Schenck]

For comparison you need to know the amperage draw. The typical 12 volt marine stereo is going to draw 5 amps to 10 amps. All my Clarion specs state is "less than 15 amps". Your boom-box specs don't provide the 110v amp draw. But it does state that you can run it 30 hours off of eight D size batteries. On the dock you don't care. Away from the dock you could run it off a small, cheap inverter. But if the boom-box draws 1 amp of 110v then roughly that is 10 amps from your battery bank. And it is probably higher.

Any friend that has ever worked on a car stereo can help you install a new marine stereo like this JBL.
http://www.overtons.com/assets/prodman/79919.pdf

 

[Brianthomas]

Thanks so much for the response Ed.

Just taking a step back to make sure I am understanding shore vs. boat power:

- when I am running off of shore power, it is 110v
- when I am running off the battery bank, it is 12v but my boat has built-in inverters so I am still able to use devices through the electrical outlets. But doing so, normal "wall outlet" devices are typically used on with 110v so will probably have higher amperage draw than 12v devices
- on shore power, I wouldn't be able to use 12v devices unless I turn my battery selector on, but at the same time could turn on the battery charger to counteract usage

Am I in the ballparck here?

 

[Clark]

Thanks so much for the response Ed.

Just taking a step back to make sure I am understanding shore vs. boat power:

- when I am running off of shore power, it is 110v
Ans. = yes
- when I am running off the battery bank, it is 12v
Ans. = Yes
but my boat has built-in inverters so I am still able to use devices through the electrical outlets. But doing so, normal "wall outlet" devices are typically used on with 110v
Ans. = true so far,
so will probably have higher amperage draw than 12v devices
Ans. = Yes but only because inverters are not 100% efficient.
- on shore power, I wouldn't be able to use 12v devices unless I turn my battery selector on, but at the same time could turn on the battery charger to counteract usage
Ans. = Yes but only up to the max capacity of the charger. If the charger can put out 10A and your loads are 15 A, you'll be drawing 5A out of the battery to supply the load.

Am I in the ballparck here?

Thoughts are imbedded in your note

 

[Clark]

I'll also throw in an example. Suppose you have an AC fan that draws 110 watts. When plugged in to an AC outlet it will draw 110w/110v = 1 amp. If you are running off of an inverter, your fan will still draw 110w at 1A but the inverter is only 80% efficient so it takes 137.5 watts out of the battery to power the inverter. That translates to 137.5/12 = 11.5 Amps DC. If you do that for 4 hours, the total draw is 4(11.5) = 46 AH.

 

[Brianthomas]

I'll also throw in an example. Suppose you have an AC fan that draws 110 watts. When plugged in to an AC outlet it will draw 110w/110v = 1 amp. If you are running off of an inverter, your fan will still draw 110w at 1A but the inverter is only 80% efficient so it takes 137.5 watts out of the battery to power the inverter. That translates to 137.5/12 = 11.5 Amps DC. If you do that for 4 hours, the total draw is 4(11.5) = 46 AH.

Thank you both, I think I get it now. For AC devices, use 110 (I thought 120v was more common?) in the denominator for calulating amps in AC, use 12 in the denomintor for calculating amps in DC. Amperage draw of an AC device running off of an inverter is scaled up by roughly 10x (plus effect of inverter inefficiency). Wattage of the device is of course constant no matter which power source.