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Old 18-03-2008, 11:45   #1
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AGM batteries in engine space?

I've seen many sites on the Web which say you can mount AGM batteries in pretty much any orientation except upside-down, and they don't need to be mounted inside a battery box. They can even be installed in living spaces because they don't vent hydrogen in any dangerous quantities. They say the only real caution is to make sure the terminals are protected from accidental shorting. Then they go on to say "check with Coast Guard recommendations for specifics."

Well, I checked and haven't found anything yet. Can I install AGMs on their sides, in the large, well ventilated, engine space on Beausoleil without putting them in a box? I'm talking four L16-type AGMs (Fullriver DC400-6) on edge on their sides, and mounting a plexiglass shield to protect the terminals. I want to avoid having to fab a custom box for them.

Can someone point me to any USCG or even ABYC recommendations on this? I checked ABYC's E-11 pub for electrical systems and came up empty.
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Old 18-03-2008, 12:54   #2
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They can be installed at any angle even upside down. Ventilation is not an issue but heat can be. That said they do need to be secured not just loose as a flying AGM in the head and it's lights out. Upside down might make it hard to attach the cables. So within those limits it's pretty flexible.

Engines rooms get hot and battery performance is best in a cooler location so ventilation for cooling is to your advantage. Batteries absorb faster when cooler so you can charge them quicker at a high rate.
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Old 18-03-2008, 13:46   #3
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Batteries donít necessarily have to be mounted within a battery box. The terminals must be protected, there must be provision to collect any spilled electrolyte, and and vented gases must be ventilated. This applies to ALL battery types.
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Old 18-03-2008, 13:57   #4
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I would not want them in that hot environment.
What if one cracks? Do they leak any liquid?
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Old 18-03-2008, 14:13   #5
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The temperature environment of the batteries is a factor to how well they can accept charge. I suspect that the ambient temps in a hot engine room is not advisable.

The optimal location is on the CL and low as possible in the bilge.
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Old 18-03-2008, 14:26   #6
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Quote:
The terminals must be protected, there must be provision to collect any spilled electrolyte, and and vented gases must be ventilated. This applies to ALL battery types.
AGM's do not vent (they have none) and they won't spill. They really have very little in the way of flowing liquid and are air tight.
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Old 18-03-2008, 14:59   #7
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Originally Posted by defjef View Post
The temperature environment of the batteries is a factor to how well they can accept charge. I suspect that the ambient temps in a hot engine room is not advisable.

The optimal location is on the CL and low as possible in the bilge.
Of course, in the case of an aft cockpit Formosa 51, low in the bilge on center line is right underneath the oil pan of the engine .

As big a boat as the Formosa is, there just isn't much space for a single large battery bank anywhere other than under the salon sole - sharing space with the engine. The only other space is under the midship cabin to port, but she already lists a bit to port anyway due to the water tanks and the genset already being on the port side (hence placing the batteries to starboard for their righting moment). And I'd have to move the water tanks!

I don't have actual temperature readings while the main engine is running. The engine space is well vented - two large bilge blowers, so it remains relatively cool. And it has a huge volume - probably more than 250 cubic feet total (inclusive of the engine, and aluminum fuel tanks - 300 gallon worth to serve as heat sinks of sort). The Westerbeke 120-T4 has a 4" exhaust system, so it can move a huge amount of heated exhaust gases and water, so I'd imagine that helps a bit as well.

Ideas?
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Old 18-03-2008, 15:05   #8
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You need to put them some place. Also look at the distances you need to run the large lines to and from the charger and windlass. Those wires are $$ / ft. Making the location central saves more money in wire than you might think. If in the end they have to go in the engine room then just be mindful of the heat. Temperature sensors for the battery charger would be important at that point.

Make sure you can set all the charging equipment up for AGM batteries. Get a volt meter and really test it. Getting the charging profiles wrong on AGM's will have you cursing the day you spent that kind of money. The two group 4's I bought three years ago are now double the price.
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Old 18-03-2008, 18:34   #9
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Max charging temperature

The maximum internal battery temperature when charging cannot equal or exceed 120 deg. F. You are correct, in that most diesel engines are so well cooled that on the level with and below the engine I would be surprised to see the battery reach much above 90 deg F unless you are operating in the area near Iraq.

You should be able to measure the ambient temperature where you plan to mount the batteries when you make a hard run with the engine to verify this.

I have an AGM start battery 6 inches from the lower part of the engine block and it never even gets warm. Good ventillation is the key.
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Old 18-03-2008, 19:29   #10
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I would be surprised to see the battery reach much above 90 deg F unless you are operating in the area near Iraq.
I am nowhere near Iraq but I can guarantee you that in FL in the summer (or for most of the year for that matter) the inside of engine compartments is a lot higher than 90.

Just my opinion. I never put a thermometer in there with my head.
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Old 18-03-2008, 22:23   #11
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The batteries are usually placed in the engine compartment of power boats - I am very familiar with biggish very powerful power cats where the engine compartment is so full of engines and stuff that there is just crawl space in them and have put those into service in tropic temperatures.

Maximum induction air temperature requirement for the engines is usually expressed by the engine manufacturers in a relationship that gives x degrees above ambient, and in the tropics that can be pretty warm . I can't imagine any problem at all with the batteries within the same temperature limits as the engines are allowed as long as there is temperature compensation on the charge controller to prevent gassing.

Battery life is supposed to be reduced by operation at high temperatures but, on the other hand, they charge to 100% when in a warm environment as opposed to not reaching 100% in a cool one (still well above freezing). So it may be that from a service life point of view running them at high temperatures is better or no worse than at coolish temperatures where they do not fully charge and sulphation is a risk (maybe someone knows?)?

As an aside, in my experience batteries of whatever type are always boxed in an acid resistant material, regardless of the battery type.
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Old 19-03-2008, 18:54   #12
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Fla water temp

I used to live on my boat in S. Fla and the water temp never got over 80 something. If the bilge and bottom of engine are well ventillated the battery might never get more than 5-10 degrees hotter than the water temp.
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Old 20-03-2008, 03:35   #13
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Quote:
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I used to live on my boat in S. Fla and the water temp never got over 80 something. If the bilge and bottom of engine are well ventilated the battery might never get more than 5-10 degrees hotter than the water temp.
Summer ocean water temperatures of 86 degrees F are common off Miami, and I would expect slightly higher on inland ICW & canals.

Ventilation cannot cool a space beneath ambient air temperature, and cooling decreases dramatically as Delta T reduces.

Accordingly, I can envision a typical small engine compartment reaching temperatures over 120 degrees F, when the engine is operating at 180 degrees, sitting in 85 deg water, and ventilated with 95 deg outside air.

Cooling by ventilation:
btu/hr removed = CFM x 1.085 X delta T
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