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Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems
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  #1  
Old 04-16-2012
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Battery Switch

So I thought I knew something about boat wiring because I could install a autopilot, VHF, 12v fans..ect, you get the point, until I started reading Nigel Calders' book and I've come to the conclusion that I know nothing regarding 12v electrical systems.

I have a 27 year old Tartan 33 with 7 year old Group 24 Deep Cycle AGM batteries that either need to be replaced immediately or will shortly. I also have a Phase 3 Battery Charger and a Balmar voltage regulator. I'm trying to draw a schematic and due to the routing of the cables, I'm not sure how the battery switch is wired. So checking the starter solenoid post and the engine ground with a volt meeting, I get these readings:

Battery switch off- no volts
Position 1- 12.6v
Position 2- 11.8v
Both- 12.2v

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.

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Old 04-16-2012
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Re: Battery Switch

Well the standard 1-2-both-off switch would connect the starter post to either battery bank. So no, that's not surprising if that's how it's set up. How do you use this switch? Those voltages look to me like you may have a bad battery (or discharged battery) at position two reading only 11.8 volts. The fact that it reads somewhere in the middle on both seems consistent with this and a standard 1-2-both-off switch. Note that means when you're on both without the engine running battery 1 is "charging" battery 2. You don't want this.

That said I know electricity better than boats and standard set-ups. Other people may be able to read more into this.
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Old 04-16-2012
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Re: Battery Switch

Thanks for the reply. I've only had the boat for two seasons and I always used both position(off when away) and I never had an issue. I sail most every weekend with one or two week long trips. There's no AC or fridge. The biggest energy draw is the autopilot and the nav lights. I'm on a mooring.

Looks like I need to pull apart the wiring to know what's going on. On a side note, I've always had problems with the tack. At times it reads high and then doesn't read at all. The original wiring diagram has the tack lead off the alternator. On the alt installed, there's a plug leading to the Balmar regulator. I don't know how the tack is connected.
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Old 04-17-2012
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Re: Battery Switch

Seven years of use would be about an average life expectancy of a lead/acid battery. Some people get much longer use (10+ yrs).
I'm not sure about AGM's life expectancy.

The OFF-1-BOTH-2 switch could be misleading. Folks tend to talk about a "house" bank and a "starting" bank. I think, in your case with 7 group 24 batteries you should think of your bank with the largest number of batteries as the "house" bank and the smaller of the two as the "starting" bank.
Use the house bank for cabin lights etc and the starting bank will get your engine started in the morning.
What size alternator does your engine spin to charge those 7 batteries? Perhaps you need more recharging capacity or just run the engine more if the alternator has the amps to recharge your banks. Solar, wind and/or shore power?

Your bank 2 with 11.8V is too low and likely needs replacement. Can you start your engine using just this bank as the power source?
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Old 04-17-2012
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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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Old 04-17-2012
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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.
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Old 04-17-2012
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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.
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Old 04-17-2012
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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.
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Old 04-17-2012
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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
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Old 04-17-2012
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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.
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