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Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems > Battery Switch
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Thread: Battery Switch Reply to Thread
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Topic Review (Newest First)
04-17-2012 02:56 PM
BarryL
Re: Battery Switch

Quote:
Originally Posted by njadventure View Post
I'm leaning towards two std deep cycles. Your summation sounds right, but others have cautioned about changing the battery switch from any position with the engine running. They mentioned momentary movements through the contacts may damage the alternator.
Thanks
It's easy to see if changing the battery switch from 1 to 2 or both, etc. will damage the alternator. Just turn on a few cabin lights and then change the switch. If the lights blink off or dim when you change the switch, the alternator can get damaged. If the lights do not change, then the alternator will be fine. This is because some (most) switches are called 'make before break' meaning that they MAKE the new connection before BREAKING the old connection. This means the electric circuit is continued the entire time. Some switches (I have never seen or heard of one but they could be out there) are 'break before make' meaning they BREAK the old connection before MAKING the new connection. In this case, there is no circuit for some time and the alternator power will have no where to go and could damage a diode.

Good luck,
Barry
04-17-2012 02:22 PM
mitiempo
Re: Battery Switch

Quote:
Originally Posted by njadventure View Post
I'm leaning towards two std deep cycles. Your summation sounds right, but others have cautioned about changing the battery switch from any position with the engine running. They mentioned momentary movements through the contacts may damage the alternator.

I really need to get my hands around how the boat is wired. The weekend is suppose to be raining so that will give me the opportunity to start pulling wires.

Thanks
If the addition I mentioned - either ACR or Echo Charge - is added and the charging all goes to the house battery the switch can be put in any position including "off" without an issue.

Starting a small diesel can be accomplished easily with almost any size house bank so switching to start is not necessary. It creates the simplest system possible and switching will not cause any issues while the engine is running.
04-17-2012 02:19 PM
mitiempo
Re: Battery Switch

I would use a start battery as the start/emergency battery. A dual purpose is just a glorified start battery, not a cycling battery like a true deep cycle.

A deep cycle battery or batteries in the house bank would be my choice, with the least expensive group 24 start battery as the start/emergency battery.
I would start on the house bank. Deep cycle batteries do not have as many cranking amps but in a larger bank or larger battery it is not an issue.
04-17-2012 01:57 PM
njadventure
Re: Battery Switch

The boat is on the hard. I don't launch for a few weeks assuming the new heat exchanger arrives.

I'm leaning towards two std deep cycles. Your summation sounds right, but others have cautioned about changing the battery switch from any position with the engine running. They mentioned momentary movements through the contacts may damage the alternator.

I really need to get my hands around how the boat is wired. The weekend is suppose to be raining so that will give me the opportunity to start pulling wires.

Thanks
04-17-2012 01:54 PM
asdf38
Re: Battery Switch

Quote:
Originally Posted by mitiempo View Post
One cranking and a deep cycle bank large enough for your needs makes sense. The 6 volt batteries I suggested are the most durable and the best bang for the dollar and 2 in series will give you about 225 AH @ 12 volts.

No manual for the alternator? If you google the numbers stamped of it you should be able to find its output. Failing that a clamp ammeter on the positive output with the engine running and the batteries in need of a charge will give you actual output.
Isn't it always worth considering a dual purpose or deep cycle for the 'starting' battery? So long as it can put out the cranking amps necessary it seems better to have that reserve available. It seems unlikely that the additional cranking amps from a pure starter are necessary.
04-17-2012 12:50 PM
BarryL
Re: Battery Switch

Hey,

I'm a little confused. In your post below you state that you turned the battery charger on and read 13.8V. In another post you stated that you were on a mooring. So I assume you are not connected to shore power. If so, how did the battery charger get power? I don't mean to insult you, but a battery charger takes AC (Shore / 110V / whatever you call it) and converts it to DC power to charge batteries.

You also stated that you can't run the engine. How long have the batteries been sitting without a charge? It's possible that the low battery just needs a charge. However, since the batts are 7 years old, you should probably just replace them.

Regarding the concepts of 'battery banks' you have received a lot of information and can make your own determination on what is best. Personally, I don't see anything wrong with your current setup, as long as you understand it. Clearly, the 'best' set up is a smart controller that ties all batteries together when charging, automatically disconnected when not charging, and provides 'emergency' connection manually. However, you can do all that yourself by just remembering to change the battery switch.

If I were you, considering your description of your needs and how you use the boat, I would buy two new deep cycle batteries. I would buy standard lead acid deep cycle, with the highest AH rating I could find. The batteries would be the same type. Small marine engines (diesel or gas) do NOT need a high amperage starting battery. The typical deep cycle marine battery will provide more than enough current to start the engine. Install them just as you have now. To start the engine, set the battery switch to 1. When the engine is running change the switch to 'both' and leave it there while the engine is running. Both batteries will be charged. When you turn the engine off, change the switch to '2'. Battery '2' is now your 'house bank' and all electrical loads will be supplied by that battery. When it's time to start the engine, just start it (with the switch set to '2'). After the engine starts switch back to 'both' so both batteries get charged. Battery '2' will accept most of the charge while battery 1 just passes the charge off to battery 2. If Battery 2 is too weak to start the engine (perhaps you spend a night or two at anchor or sailed for a VERY long time) then switch to battery 1 and start the engine.

If you remember to change the battery switch yourself, there is no need to modify your electrical system. Just be sure to never change the battery switch to 'off' when the engine is running.

Barry




Quote:
Originally Posted by njadventure View Post
I didn't check voltage at the batteries which I will do the next time. I did turn on the battery charger and the voltage read 13.8 in the both position.

So my first of many questions to come is should I have seen voltage at the starter post in both position 1 & 2. In my limited knowledge, I would think if one battery was dedicated as a starter and the other as a house, there would no voltage in one of the positions. I could be way off in my thinking.

Thanks
04-17-2012 06:23 AM
njadventure
Re: Battery Switch

Thanks. I've been considering using 6v batteries for the house bank, but I'm running into a space issue. I really liked Maine Sails post regarding Sam's Club batteries. For the buck, it looks like a great deal.
04-17-2012 06:07 AM
mitiempo
Re: Battery Switch

Quote:
Originally Posted by njadventure View Post
There are only 2 batteries installed. Both are 7 year old, group 24 AGM deep cycles. I thought both were fully charged when I tested. I need test again starting at the batteries.

I'm wondering if/ when I replace them, if I should install one cranking and one deep cycle. It seems to be the popular choice.

I'm waiting on a replacement heat exchanger so I can't run the engine. I couldn't find the stamping on the alternator to determine the amps. Does anyone have a easy way after I get the engine running?

Thanks
One cranking and a deep cycle bank large enough for your needs makes sense. The 6 volt batteries I suggested are the most durable and the best bang for the dollar and 2 in series will give you about 225 AH @ 12 volts.

No manual for the alternator? If you google the numbers stamped of it you should be able to find its output. Failing that a clamp ammeter on the positive output with the engine running and the batteries in need of a charge will give you actual output.
04-17-2012 06:01 AM
mitiempo
Re: Battery Switch

Caleb

I think he has batteries that are 7 years old. Doubt he has 7 batteries - more likely 1 in each bank or possibly 2 house 1 start.

nj

What you are measuring makes sense. Both batteries(or banks) are wired to the switch in the #1 and #2 positions. Whatever you select is output to the house loads as well as the starter.

The 11.8 volts as posted sounds ready for replacement.

Your measurements were each battery individually and the 12.2 was the batteries combined, the bad bringing down the better one.

A battery that is not on charge and is resting is considered fully charged at 12.7 volts, slightly higher with some. 12.1 is about 50% charged.

If you are on a mooring and do not have solar to keep the batteries fully charged Agm batteries are not a great idea. They like to be fully charged as often as possible. An alternator, even with an external Balmar reg will not do this as the batteries internal resistance slows current to a crawl for the last 15% of so and it takes many hours. A 40 or 50 watt solar panel will top them up and keep them fully charged as you are not on shore power.

On many boats I see the switch is left in the both position. This is the fault of wiring the charging through the switch, common on many boats but not without its issues combined with operator confusion. You need to be on both to charge both. If you forget to switch to #1 or #2 after charging you will drain both batteries. And if you or someone else switches to or through off with the engine running damage to the alternator diodes will likely occur.

The solution is to route all charging to the house bank directly - it is usually the largest bank and needs the charging more than a start battery. The start battery is charged by either an ACR or Echo Charge. These are a bit different but will both automatically allow the start battery to be charged without any input from you. The 1/2/both/off switch then becomes a "use" switch only.

The best value for battery replacement would be 6 volt golf cart batteries - flooded, not Agm - in series as a house bank and a 12 volt start battery. This could be used in several ways. You could start the engine with the start battery and when anchored switch to the house bank or alternatively you could use the house bank for everything and keep the start battery as an emergency battery.

As far as the tach if you look in the Balmar regulator manual (if you don't have it you can find it online at Balmar) it will show the regulator wiring and where the tach is wired in.

Way more than you asked for but I couldn't sleep.
04-17-2012 05:49 AM
njadventure
Re: Battery Switch

There are only 2 batteries installed. Both are 7 year old, group 24 AGM deep cycles. I thought both were fully charged when I tested. I need test again starting at the batteries.

I'm wondering if/ when I replace them, if I should install one cranking and one deep cycle. It seems to be the popular choice.

I'm waiting on a replacement heat exchanger so I can't run the engine. I couldn't find the stamping on the alternator to determine the amps. Does anyone have a easy way after I get the engine running?

Thanks
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