Adding another battery

[Lazy1]

Just wondering and making conversation...

My C22 has all the normal electrical stuff (lights, some LED) plus VHF and a car stereo with four speakers and maybe a depth sounder soon. It also has a 6 watt solar panel and a Tohatsu sailpro so I can get some power that way.
I have an Interstate SRM-24 with 81 amp hours so where would a 2nd battery be added on a "new design"?
I'm thinking in the volcano area or further forward (dinette) with some long battery cables to the existing rear battery? Would relocating both to the front and cabling to a rear buss bar for charging be better (trailered)?

Is matching amp hours on parallel batteries critical?

 

[Gene Neill]

I have an Interstate SRM-24 with 81 amp hours so where would a 2nd battery be added on a "new design"?

I thought about that long and hard, and never came up with a place I liked. I finally determined that if I wanted more Ah capacity, I'd just build a box and install a bigger battery in the same place as the old one, even though the weight would be much better off further forward.

There MIGHT be room in the empty cavern just aft of the volcano, but I don't recall for sure. Two AGM's would probably fit in there on their side, I'll bet, nice and low and close to the center of the boat?

That said, for just a little more money (and a good bit less weight) you can always install enough solar to keep you going indefinitely. With 60 watts of solar, our 85Ah Trojan 24TMX never gets below about 70%, no longer how many days we're out. Once I discovered that, I never gave another thought to more (or bigger) batteries.

(All your lighting should definitely be LED if they are not already. That's low-hanging fruit. No need for new fixtures, just replace the bulbs with LED equivalents. This website's store has a great cross reference RIGHT HERE. )

I don't think it is advisable to wire two batteries of different Ah capacity together. My understanding is that it is THEORETICALLY possible, IF they are the EXACT same voltage (not just "12 volt", but more precise than that) AND they are the same chemistry (flooded, GEL, AGM), AND they are the same age, blah blah blah. At least that's what I've seen on the internet, so it must be true.

 

[Benny17441]

Well I would not say critical but the recommendation is that both batteries be of the same type and age. What happens is that larger and newer battery will be kind of forced to play by the older and weaker battery rules. When the weaker battery says I'm full, the battery charger may cycle off even though the stronger battery may not be full. The weaker battery will also be regularly draining off the stronger battery as the level of charge seeks equilibrium. A shorter battery life for the newer battery may result and that will translate to a few dollars. What I would do if combining the batteries would be to match the Ah of the smaller but if you decide to isolate them with a 1,2,Both, Off battery switch then you can get one larger than the other. With the switch they might only be combined in just a few instances minimizing any adverse effects of one battery over the other. You can alternate batteries per outings and just use the 2nd battery when the 1st gets weak.

 

[Lazy1]

Thanks for the replies,
I did a little spreadsheet with expected Ah budget and expected duration of each device somewhat inflated and I get almost 90A/hs for a overnight trip staying out around 30 hours. The big power eaters are the FM radio and the halogen deck light if I burn it for 8 hours over night ( I like knowing I can be seen ) and the VHF if I leave it on for the whole time.
Thanks Gene, I just ordered the LED Deck light, that should save me about 11 Ah. Cut my budget to 77 Ah!

Hope no one minds my babbling, I get sad when I don't see any posts in this forum for a few days.

 

[Gene Neill]

Wow, that's still a TON of power consumption! Enough to just about drain TWO of those 81Ah batteries in 30 hours.

The rough-draft energy budget I drew up for our Albin Vega 27 only came to 82Ah/day, and that includes running a fridge and a watermaker!

 

[Lazy1]

hmm, maybe my assumptions are incorrect?
from the googles I assumed the FM radio would consume about 5 amps per hour and guessed 12 hours over two days on the high end, and the VHF taking about .6 amps for 30 hours. That's already 78 A/hrs right?

 

[Lazy1]

Just found another forum where they said the FM radio would likely only take around 1 a/hr. That changes things a bit

 

[Don S/V ILLusion]

No clue what FM radio you have but it’s inconceivable any one would draw 5a/h. Why not rely on actual manufacturer data and check the specs

 

[Lazy1]

No clue what FM radio you have but it’s inconceivable any one would draw 5a/h. Why not rely on actual manufacturer data and check the specs

It's a Sony CDX-gt56ui and can find no such info. It has a 10 amp fuse and the amp is rated at 17W x4 continuous so I figured 40W total which is 3.33 amps and estimated up to 5ish for worst case. Maybe incorrect assumptions.

 

[Gene Neill]

My understanding is, stereo power consumption varies wildly based on volume. And maybe some other stuff. 5A does seem like a lot, but I dunno. A cheap ammeter would tell the story.

I'd be interested in what you learn about this. Since some numbnuts cut huge gaping holes in our Vega's (beautiful sapele plywood) main bulkheads for a stereo, I'm almost stuck with installing a new one in there now, since those holes are not going away.

 

[Lazy1]

My understanding is, stereo power consumption varies wildly based on volume. And maybe some other stuff. 5A does seem like a lot, but I dunno. A cheap ammeter would tell the story.

The boat is moth balled for winter now but I plan on redoing much of the electrical in early spring and I should be able to borrow a quality ammeter like a Fluke or something from work and check everything individually. A PO added Radio, VHF, Depth sounder, etc and wired everything with a dizzying array of zip ties and wire nuts to the main circuit so I can't isolate anything with switching but the lights. I plan to move the VHF to the accessory switch and add switches for FM radio and whatever else.

 

[Grotto]

The PO’s wiring of my boat. Needless to say I am starting from scratch.

 

[Lazy1]

The PO’s wiring of my boat. Needless to say I am starting from scratch.

 

[Lazy1]

holy crap, I feel better now

 

[Gene Neill]

holy crap, I feel better now

LOL! I feel your pain. I pulled a basketball-sized wad of EXTRA wire out of Daydream, just cleaning it up so I could see what was what.

Since you have a new design ... here's what I did to create a little room for a realistic amount of wiring. I took the first pic of the bus bars lying on my back, head aft, just a couple inches aft of the panel. The solar controller is also on the starboard side, down where the jolly green giant's feet would be.

 

[Hardhead]

Gene - that really looks 1st class. Gotta admire any sailor with varnished mounting boards. If I can ask, how did you attach the boards to the underside of the cockpit coaming? Also, did you screw into the liner on the bottom photo?

 

[Lazy1]

That's an envious setup you got there
[edit] even enviable

 

[Gene Neill]

Gene - that really looks 1st class. Gotta admire any sailor with varnished mounting boards. If I can ask, how did you attach the boards to the underside of the cockpit coaming? Also, did you screw into the liner on the bottom photo?

Thanks - those boards were actually scraps of sapele plywood, taken from our Albin Vega. I stuck them on with thickened epoxy.

The bottom two screws under the controller go into the liner, the top two just go into the teak trim board.

 

[Lazy1]

@Gene Neill
I have made a choice and based on your setup I have a few questions...

• What did you use to mount you panels to the rail clamps?
• Do you think a single rail clamp would be sufficient to support one panel?
• Did you chose to not use the Load output terminals on the Victron to supply power to the boat for ease of install, or is there a functionality problem or risk that I should consider? (wondering a battery protection mode would cut off lights when I would rather run the battery to the ground before losing something like a anchor light, paranoia?)

I got a Victron Smart solar 75/10 and a 30 watt panel and trying to work out the details.

Thanks for your advice!

 

[Gene Neill]

@Gene Neill
I have made a choice and based on your setup I have a few questions...

What did you use to mount you panels to the rail clamps?

Pieces of 1/2" starboard (okay, actually pieces of a 1/2" cutting board I found in a clearance bin ... don't judge me ...)

Do you think a single rail clamp would be sufficient to support one panel?

Definitely not.

Did you chose to not use the Load output terminals on the Victron to supply power to the boat for ease of install, or is there a functionality problem or risk that I should consider?

I couldn't really see any use for the load terminals, your mileage may vary.

(wondering a battery protection mode would cut off lights when I would rather run the battery to the ground before losing something like a anchor light, paranoia? )

Probably.

I got a Victron Smart solar 75/10 and a 30 watt panel and trying to work out the details.


Thanks for your advice!

Any time!