Your thoughts about how to wire stereo amps, etc.

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steve1313
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Your thoughts about how to wire stereo amps, etc.

#1 Post by steve1313 » Wed Dec 12, 2018 12:41 pm

I'm ugrading the sound system this winter and I'm curious to know how others wire their amps, etc.

My current setup is two AGM batteries wired to a basic Blue Sea Battery switch (1, 2, 1+2, Off). Currently, I have a powered subwoofer, which is wired directly to Battery #2. Everything else electrical on my boat (including the stereo head unit) is wired to circuit breaker protected switches in the console. I plan to replace the subwoofer with a larger one with it's own amp, and add a four or six channel amp to power the speakers throughout the boat. I know that it's typical to wire amps directly to the battery which is what I'll probably do.


If I do that, what's the best way to manipulate my battery switch to keep both batteries charged? Obviously Battery #2 will get discharged faster than battery #1, since it will have almost no current draw when we're anchored or floating. At that point, only the head unit will be drawing power and that will be minimal since the amps aren't in the head unit. Should I run the boat with the battery switch to #2 most of the time, insuring that the battery that is getting used the most stays charged? I'll still have battery #1 available for starting if I ever completely run down #2 while at anchor. Should I run the switch at 1+2 when under power to make sure both batteries get charged? Should I add an automatic charging relay (ACR), even thought I know that doesn't just charge the battery that needs it the most?

FYI, I don't have or plan to have an onboard charger (powered by shore power). I think it's overkill especially with AGM batteries that will hold a charge for a long time!


Just curious to see what others do or would do in this type of setup! Thanks for your input.
Steve
"Serendipity" - 2017 Sweetwater 2286 WB Tritoon w/ 150HP Yamaha
Slipped at Lake Anna, Virginia
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Marc K
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Re: Your thoughts about how to wire stereo amps, etc.

#2 Post by Marc K » Wed Dec 12, 2018 1:46 pm

I’m a simple three position (A, B and A+B) switch kind of guy. With a voltmeter, I can make the best decision on what is needed, at given moment.

In my particular case, I have a dedicated AGM start battery that handles the engine, instruments and running lights. I have large batteries that serve everything else and only get plugged into a charger in my boat house when I return daily. I have little maintainers that I connect when I know that I won't be going out for a few weeks.

AGM brands/types have vastly different characteristics between them, but in general:

Mine lose 1% of their charge per month in cold weather. They have a freezing point of (-)90F when fully charged. The self discharge rate climbs to 2% to 3% in hot weather.

Sulfation begins to form on the plates as you draw down to about 80% to 85% state of charge. As you go lower, they form faster. This is normal and they get converted back when you reach 100% state of charge. Clearly understanding when a full charge is reached, is critical because the sulfates will harden up with time. Most people trust the charger to know, but they are often wrong because batteries have different requirements.

Acceptable depth of discharge is highly variable between types, with some designs being quite happy at 80% - 90% depth of discharge, others will quickly die with that usage.

My point? Knowing how far you can discharge is critical to protecting battery service life. Knowing when to charge and for how long are just as critical. A voltmeter will tell you A LOT when you know what to look for.

Marc
Big and ugly but we love our 1999/2000 Crest II DL with a Yamaha F115

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steve1313
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Re: Your thoughts about how to wire stereo amps, etc.

#3 Post by steve1313 » Thu Dec 13, 2018 3:55 am

Marc-
Thanks for your response. All good information. I've thought about adding a voltmeter, maybe something like this. https://tinyurl.com/y7v85sa2 Of course, I'd have to add switches to keep the meter from being on all the time and draining the batteries.

Curious why you use maintainers? With such a small (1-3%/month) drain, it doesn't seem necessary. I've always been of the mindset that chargers/maintainers can do more harm than good as they charge the battery when it really doesn't need it.

Of course the other side of the equation is recharging the batteries. I think my alternator on my Yamaha 150 puts out 35 amp at WOT. I wonder how much time it would take to recharge batteries that are partially discharged.
Steve
"Serendipity" - 2017 Sweetwater 2286 WB Tritoon w/ 150HP Yamaha
Slipped at Lake Anna, Virginia
Primary Residence: Richmond, Virgina
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Oldchuck
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Re: Your thoughts about how to wire stereo amps, etc.

#4 Post by Oldchuck » Thu Dec 13, 2018 6:31 am

Steve,
Your 150 will indeed put out 35 at WOT but it takes some amps just to power the engine management systems as well as all the draw your instruments and on board systems are using. That can easily be calculated.

The 150 although my favorite engine does not have a really high rate of charge in todays' world of more advanced engines but is more than enough provided you do not draw your batteries down too far. Remember many autos/trucks have 100-140 AMP alternators and they do not usually sit idle for as long as many boats.

I see 2 choices: 1) Either add a switch like Blue Seas automatic charging switch that will automatically switch to whichever battery is low or needing a charge or stop the charge when up to capacity. OR 2) Like Marc, Go to voltmeters with a switch so you can manually check the status of each battery and you will soon be able to figure out what the rate of charge is for specific usage of certain electrical equipment. OR I guess you can leave it as it is and over time see what your rate of discharge is using a manual voltmeter to check each battery during usage to ascertain amps used....

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Marc K
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Re: Your thoughts about how to wire stereo amps, etc.

#5 Post by Marc K » Thu Dec 13, 2018 7:28 am

Yep, you are right!

If a deep cycle AGM is fully charged it can indeed sit for several months without harm. 99% of Gel/AGM/Flooded deep cycle batteries die from sulfation (undercharging) so I tend to go for overkill. But my frame of reference is often a customer driven requirement of a 10 year battery bank service life.

A good maintainer will hold a steady “Float” voltage (13.1v to 13.7v is required, depending upon the AGM brand) This float voltage holds the battery harmless – it’s not discharging or charging. Using the wrong float voltage for the particular battery is indeed harmful. Again, you are correct – it really isn’t needed with a good AGM for most boating applications with a true disconnect.

When a high quality AGM battery is being charged at the required 14.xx volts it will draw less than 0.05% of its amp hour capacity when it is fully charged. So that’s ½ amp per hundred AH of battery. Think of the old chargers we had in our garage with a needle. It would slam over to high amps and slowly come down. People tend to think that the charger is tapering the amps, but it is actually the battery gradually drawing less current as it fills up.

Most modern chargers use 2% to 3% current draw as being 100% charged - which results in undercharging. Terminating the charge cycle before the battery is 100% charged causes premature sulfation of the plates. 85% to 90% charged is not “close enough” if you want the best life that the battery can give you.
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Marc K
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Re: Your thoughts about how to wire stereo amps, etc.

#6 Post by Marc K » Thu Dec 13, 2018 8:09 am

Some more info. Time to reach full charge:

Using a 100 ah AGM battery as an example: If you drain it by 70 ah, you have to put back more than that because nothing is 100% efficient. The efficiency of AGM's is much higher than flooded batteries, and the number varies by manufacturer, but 4% to 10% is a typical range.

For simplicity I'll use an example of 70 ah that needs to go back into a battery, and a charging source that gives me 10 amps.
On the surface, that would seem like 7 hours to charge the 70 ah back.....but it isn't. It will require 9 hours.

Remember that as the battery charges up, it will begin to draw less amps. The battery will draw the full 10 amps until it reaches about 80% charge, then begins to taper. That final 20% takes about 2 hours and it is critical to avoid sulfation of the plates.

Marc
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Re: Your thoughts about how to wire stereo amps, etc.

#7 Post by Marc K » Fri Dec 14, 2018 9:41 pm

Added clarity sake:

If you draw the battery down by only 20%, you still need ABOUT 2 hours to fully charge it - even if you have a huge charger. This is because the battery simply won't draw the available amps as it nears full charge.

As a healthy battery charges and discharges. the impedance changes. I often use water when I teach this stuff to groups of people with varying backgrounds.

How much water (amps) does a dry sponge (battery) suck up?
Answer: As much as it can, as fast as it can.

How much water (amps) does a wet sponge (battery) suck up?
Answer: Essentially none - because it's full.......

OK, unless someone has a question, I will shut up for now.........
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Re: Your thoughts about how to wire stereo amps, etc.

#8 Post by jrolin1 » Sat Dec 15, 2018 6:26 am

I have three amps and two subs. One amp is for the rear facing speakers and is only on if we are hanging out behind the boat. I have a power distribution block for the amps that is connected to the perko switch. So one larger wire (heavy gauge) goes to the switch. Both batteries are large capacity. We don't go around blasting at loud volumes but like a good sounding system. I have not needed to connect to a shore charger. The volt meter can help you know how the battery charge is. In my case once it gets slightly over 14 volts on the trip back with the motor running the battery is mostly charged. You can check a battery charge by the at rest voltage after it has been sitting for a few hours. I switch between the batteries to keep each one topped off. This setup has worked fine for me for 8 years. I have rarely needed to hook a charger up to the batteries. If you run at volume and have a short trip back you may need to charge the batteries. Use the chart to check battery state. Temps can affect the chart a little but I don't use it in really cold weather.


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Marc K
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Re: Your thoughts about how to wire stereo amps, etc.

#9 Post by Marc K » Sat Dec 15, 2018 11:48 am

That is a great chart for conventional flooded cell batteries, and folks who use them should memorize the numbers.
AGM's are very different.
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steve1313
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Re: Your thoughts about how to wire stereo amps, etc.

#10 Post by steve1313 » Sun Dec 16, 2018 3:51 am

First, thanks to everyone for their contributions and information. This is an interesting thread that is probably going to increase the scope of my stereo project, because I'm probably going to add a voltmeter, power distribution block and more. But for me, doing these kind of projects is half the fun of having a boat!

After looking at the chart jrolin1 posted and seeing Mark K's comment that AGM's are different, I went in search of a similiar charge specifically for AGMs. Of course, I found numerous charts for all kind of batteries, and most of them differed from each other, regardless of battery type. Here's one I found for AGM's, but who knows how accurate it is.

The way we'll use our system will be similiar to jrolins, so I probably don't have too much to worry about, but I usually overengineer stuff rather than just assume things will be OK. LOL :biggrin2
chart2.JPG
chart2.JPG (29.05 KiB) Viewed 3012 times
Steve
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Re: Your thoughts about how to wire stereo amps, etc.

#11 Post by jrolin1 » Sun Dec 16, 2018 7:13 am

Marc K wrote:
Sat Dec 15, 2018 11:48 am
That is a great chart for conventional flooded cell batteries, and folks who use them should memorize the numbers.
AGM's are very different.
That is why I posted both. Is the AGM not visible? I see it is not when I looked in another browser. It shows up in Chrome but not edge. Strange. It was the same one Steve has. Next time I will do it as an attachment.

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Marc K
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Re: Your thoughts about how to wire stereo amps, etc.

#12 Post by Marc K » Sun Dec 16, 2018 7:42 am

Steve,

This is a brand specific thing, but your chart is exactly how many of the higher end AGM's are - but.............. 10.5v is 0% remaining when measured under load. The other numbers are "at rest."

If you discharge down to 10.5v then disconnect the load and let the battery sit, it will gradually rebound to around 11.2v to 11.6v. Same thing happens at other points on the discharge curve. So, if you find a battery that is reading 11.2v or lower in a resting state, it is fully depleted. If lower, it is already being damaged.

Sulfation of the plates begins with a standing voltage somewhere between 12.5v and 12.6v for most deep cycle AGM's (80% - 85% state of charge) and rapidly accelerates at lower charge levels.

Temperature has a very, very small impact on standing voltage at 0.6 mv per degree F. (About 0.05v at 0 degrees F)

Have you calculated the amperage draw and what to expect in terms of battery voltage? (The sag in voltage under load.)
Example: A pair of Group 27 (100 ah each) battery bank at 90% charge may read 12.4v while running under a 50 amp load and 12.7v with a 20 amp load.

Deka is different vs. Odyssey vs. Optima vs. Lifeline vs. FullThrottle, etc.

Marc
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Re: Your thoughts about how to wire stereo amps, etc.

#13 Post by Marc K » Sun Dec 16, 2018 7:45 am

jrolin1 wrote:
Sun Dec 16, 2018 7:13 am
Marc K wrote:
Sat Dec 15, 2018 11:48 am
That is a great chart for conventional flooded cell batteries, and folks who use them should memorize the numbers.
AGM's are very different.
That is why I posted both. Is the AGM not visible? I see it is not when I looked in another browser. It shows up in Chrome but not edge. Strange. It was the same one Steve has. Next time I will do it as an attachment.
Understood! I just fired up Chrome and the AGM chart shows above the flooded.
(Can't see it in Firefox)

Marc
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steve1313
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Re: Your thoughts about how to wire stereo amps, etc.

#14 Post by steve1313 » Mon Dec 17, 2018 3:16 am

I haven't calculated the amp draw yet because I'm still trying to decide on which amps, etc. to buy.

FYI, here's the batteries I have https://www.interstatebatteries.com/products/34m-agm
Steve
"Serendipity" - 2017 Sweetwater 2286 WB Tritoon w/ 150HP Yamaha
Slipped at Lake Anna, Virginia
Primary Residence: Richmond, Virgina
Lake House: Lake Anna, Virginia

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