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Go Back   SailNet Community > General Interest > General Discussion (sailing related) > Basic marine deep cycle battery questions
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Topic Review (Newest First)
04-19-2013 03:41 PM
hellosailor
Re: Basic marine deep cycle battery questions

Dunno about the beta but I've used a 17AH battery to start an Volvo MD6 or MD7, I forget. All parties were happy with the result.
04-19-2013 03:31 PM
deltaten
Re: Basic marine deep cycle battery questions

I just picked up one of those small batteries from my Interstate dealer for a 10million CP spot lite. OTD price was a couple cents more than $26 !. Generally used in computer back-ups, fire/security alarm and emergency lighting. 12v AGM rated 7 AH..as is written on the side of the batt.
Whether it would start my Beta20 or not..I dunno; but it would run a buncha LED lites for quite some time.
04-19-2013 01:10 PM
hellosailor
Re: Basic marine deep cycle battery questions

The VHF will have two power ratings. One for transmit (one one for high power, one for low power) and one for receive (with squelch off).

The rule of thumb is that you will be transmitting perhaps 10% of the time compared to the receive, so if the radio draw 3A on transmit and 0.1A on receive, you would average that as about 0.39A for average power used.

You CAN also buy an "alarm and exit lighting" battery, or get a car "jump box" that has a battery like that in it, and keep that as an emergency-only battery for the radio, etc. Most of the jump boxes are big boxes with small batteries inside, so buying just the battery from a discounter can be way more effective if you don't need the box, cabling, charging cord, etc that the jumper box puts together.
04-19-2013 12:52 PM
chucklesR
Re: Basic marine deep cycle battery questions

Others have already addressed the 'what's watt' issue of amp hours and usage.
There is no such thing as a standard battery - you need to look up yours and see what it it rated at, then because you have no idea what the current state of it is (age, condition) go with a safety factor that only you can determine (i.e. 80%).
Voltage can be used as a simple indicator of state of charge, but it's not totally accurate. There are many threads here discussing that (search 'voltage state of charge').
For extra 'hang time' on the hook there are lots of options, solar, wind, low amp anchor lights etc..the idea is either put the amp's back, or reduce the use.
Be realistic on what a anchor light draws - the old ones are 1.5 or more amps per hour - for 30 bucks you can get a perfectly legal LED base hook on the back stay type and it will draw .1 amps.
Solar - calculate your gain to a charged battery based on a simple rule of thumb - you'll get 25% of the watt rating in amp hours (e.g. 100w panel, 25 amp hours) per day.
A 20-30w panel is a fine trickle charge over a week on a mooring, it will not significantly extend anchor hang time.
If budget is a concern you can get a 900w gas generator at Harbor Freight for under a 100 bucks. They are loud, smelly and use gas - but - they are cheap, almost disposable and great for that time when you do in fact kill the battery.
04-19-2013 11:44 AM
Alex W
Re: Basic marine deep cycle battery questions

If you are concerned about battery life or don't already have an onboard battery system you could also consider a portable anchor light and VHF radio. The anchor light can be raised on a halyard (using a messenger line to bring it back down). Handheld VHF radios will last about 15 hours on a charge. When kayaking I've found that to be adequate to last me more than a week if I only tune in during major crossings or when trying to hail someone.

A basic solar charging system is under $200 and really worth it. If you don't have the alternator for your outboard then I'd get the solar charger first. A 20-30w panel and a Genasun MPPT charger should keep your battery topped off and recharge for light battery use.

If you think that you'll want to add a tillerpilot down the road then a good house battery system will become a requirement.
04-19-2013 02:41 AM
mdbee
Re: Basic marine deep cycle battery questions

One problem about the outboard... that rating is the max. output at full throttle.
04-19-2013 01:10 AM
matthewwhill
Re: Basic marine deep cycle battery questions

This is very helpful. I love this site. I am planning some overnighters in the Puget Sound and just want to make sure I'll have enough juice to use the anchor light all night and use the VHF in an emergency. And also wanted to know how long I would need to run the outboard to get a decent charge back into the battery.
04-18-2013 08:42 PM
chef2sail
Re: Basic marine deep cycle battery questions

Quote:
Originally Posted by Mark1948 View Post
Didn't as the question, but this is helpful as I would like to do a night sail across Michigan if it ever stops raining and warms up enought to work on the boat. I am thinking I should have a third deep cycly in "reserve" just for added security.
Should all be part of one large bank vs separate banks

Long detailed explaination. One part of it is battery life. Here as some numbers not exact but should be close enough to explain.

Suffice it to say this- 2 battery bank
1 Battery separate from 2nd battery each 105 ah .... or
2 batteries in one bank at 210 ah

Suppose you run 50 ah in one day. Its 50% of one of the one battery banks or 25% of a battery bank with two batteries in it.

Number of deep cycles a battery gets depends how deeply discharged. Lets say its rated at 250 deep cycles at 50% and 750 at 25%

Two one battery banks you get 500 cycles ( 250 cycles out of each battery)
One two battery bank you get 750 cycles
04-18-2013 05:07 PM
Mark1948
Re: Basic marine deep cycle battery questions

Didn't as the question, but this is helpful as I would like to do a night sail across Michigan if it ever stops raining and warms up enought to work on the boat. I am thinking I should have a third deep cycly in "reserve" just for added security.
04-18-2013 04:59 PM
KBuckley
Re: Basic marine deep cycle battery questions

Googling a few things it looks like your alternator is rated for 5 amps output, a Trojan Group24 deep cycle is rated at 85 AH, an ICOM m504 VHF is rated at 5.5 amps (high power transmit) and 1.5 amps (receiving at max audio), an incandescent anchor light is probably 20W - I am lazy and this is not accurate so call it 2 amps.

To your questions:
1) I'll assume you are not a chatterbox and will only be monitoring the VHF, but you will be doing it loud enough for the whole anchorage to hear. 1.5 amps + 2 amps = 3.5amps. One hour of usage will consume 3.5 amp-hours. You have available 85 amp-hours before your battery is dead, but 42.5 if you want to treat your battery properly.
85/3.5 = 24 hours.
42.5/3.5 = 12 hours.

2) Same assumptions as in 1) and your alternator puts out 5 amps so you can assume (for the sake of this analysis) that one hour of charging will give one hour of usage.

3) As stated above, there are battery monitors that tally the current in and out of the battery and estimate the available battery capacity but I suspect for your purposes a voltmeter is sufficient IMHO.

I hope this helps,
Ken
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