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Old 02-09-2011, 11:08   #1
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Schumacher Battery Charger ?

I only have one battery and all it powers are lights and occasionaly a 12v fan. I have always used my cabin lights getting dim as an indicator of when my battery needs charging. My new (4 months old) AGM went from bright lights one evening to no lights the next night. I bought a Schumacher Marine Charger/Maintainer. It is supposed to automatically detect 6v or 12v batteries and then charge them accordingly. Upon first use, it wont go into 12v mode, only 6v. I called Schumacher and they said it will not charge a severely discharged battery in 12v mode. They said to go ahead and charge it in 6v mode. Once the battery gets enough volts in it, the charger will recognize it as a 12v battery and switch to the higher rate charge mode. Does this sound right?
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Old 02-09-2011, 11:23   #2
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Re: Schumacher Battery Charger?

Maybe "right", but not a good idea. The Schumacher isn't a real 3-stage charger.

I'd think about getting a better charger which will help prolong the life of your battery. AGMs need to be FULLY charged at least every couple of weeks, preferably more often. And, they can take a LOT of charging current.

Sizing the charger will depend on how you use your boat (mostly at dockside? at anchor or on a mooring? actively cruising?).

I'd look at the Iota charger line....very good equipment in various sizes from 15A to 90A charging capability...and relatively inexpensive. A good source is Northern Arizona Wind and Sun.

Bill
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Old 02-09-2011, 12:40   #3
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Re: Schumacher Battery Charger?

You are discharging your battery very low. This will give it a short life. Lead acid batteries, even if they are deep cycle, need to be recharged earlier than 50% capacity for a reasonable life. Shallower cycles will give a longer life.
If the charger thinks its a 6v battery its been severly disharged and may not recover, or last much longer if it does recover.
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Old 02-09-2011, 12:42   #4
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Re: Schumacher Battery Charger?

I thought the whole thing with Deep Cycle batteries was there ability to be deeply discharged and then recharged fully.
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Old 02-09-2011, 13:02   #5
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Re: Schumacher Battery Charger?

Normal lead acid batteries are designed to be discharged only 10-20%. Deep Cycle batteries are designed to be discharged around 50%.
Both types of batters can be discharged more, but their cycle life drops dramatically. Conversely if you reduce the depth of discharge they will last longer.
If you discharge a deep cycle battery down to 90 or 95% as you are probably doing its life will be very short.
You need to recharge sooner, or add more battery capacity, otherwise you find your battery costs will be high.
A system to monitor the battery discharge amount is very helpful
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Old 02-09-2011, 13:03   #6
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How is the schumacher not a 'real' 3 stage charger? I didn't see any mention of the model... The 15amp 'marine' schumachers you can find at walmart are 3 stage and fully automatic and smart regulated.

I'd go with what the folks at Schumacher told you....
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Old 02-09-2011, 13:04   #7
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Re: Schumacher Battery Charger?

Thank you. I just read a detailed article about AGM batteries. I am going to get a voltmeter installed so I can watch things better.
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Old 02-09-2011, 13:24   #8
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Re: Schumacher Battery Charger?

A digital voltmeter is helpful, but its difficult to determine the state of charge from the voltage alone. It can be done at least approximately by measuring the voltage after the battery has rested and compensating for temperature, but its not easy.
As an alternative

1. work out how much you use based on the consumption of your lights and fans and make sure you recharge well before this consumption reaches 50% of you battery capacity. If your usage is reasonably constant you may be able to say I need to recharge after X number of nights. If you can recharge earlier and this will be better for the batteries.

2. Install a battery monitor. These are more than a voltmeter. They count the AHrs in and out of the battery.
Models include the Blue seas VSM, link 10, Nasa BM-1, Victoron BMV600.
The Nasa unit is the cheapest.
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Old 02-09-2011, 14:09   #9
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Re: Schumacher Battery Charger?

Do you know anything about The Battery Bug from Argus Analyzers?
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Old 02-09-2011, 14:35   #10
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Re: Schumacher Battery Charger?

That is an interesting product.
Internal resistance is a common way of measuring the health of starting batteries, but I have never seen a monitor that does that is permantly installed to do this.
The concern is how well does this correlate to the SOC of a deep cycle lead acid battery ?
Does the intermittent discharge damage the battery? How do attached electronics cope with voltage drop?
The monitors I listed above use a different method, counting the power in and out of the battery. Its not perfect, but it is common proven technology.
I suspect that Battery bug will not be as effective, but if you get one let us know how well it works.
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Old 02-09-2011, 15:39   #11
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Re: Schumacher Battery Charger ?

For your charging you might look at a Guest battery charger. They make a small (physical size, not capability) waterproof one that is made for marine use.
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