Dryfit

[southchinasea]

This is odd, I thought I posted this about 8 hours ago..perhaps finger trouble? Anyway.......
I have just been advised the domestic batteries for my new boat will be "dryfit" Sonnenschein 2 X 135AH.
The yard tell me these are "equivalent" to 2 X 170AH "classic batteries". By this I assume they mean
wet cell. Interestingly an extra 135Ah domestic is an option which is actively encouraged.
My question is simply is the yard right or not? I am not an expert on battery chemistry but I think
the "dryfit" is a gel battery.
Thanks

 

[ccscott49]

The dryfit is gel, and very expensive, I would go for the extra battery, you never know when you might need it, or if you later fit an inverter etc. Incidently the gel batteries require a special charging regiome, with shorepower chagers for gel and alternator control box the same. I have read excellent reports on the sonneschien range of batteries, you can even turn them upside down and they work fine!

 

[HaraldS]

Good batteries. The claim that 135Ah equals 170Ah of a regular battery is not unreasonable because it is not good to discharge a regular (semi tracktion) battery to less than about 60% remaining charge, at least you shouldn't do that too often. With Gel Batteries that is much less of a problem and you can happily go down to 40%, which really means you get about 150% capacity per weight. Still I would go for the additional battery, you will never have enough. I have 6 of these batteries. I presume the yard will set the charger float voltage appropriate for your Gel battery, a too high float voltage is about the only thing they don't like.

 

[charles_reed]

Even work during a B3

That's got to be good.

Just make sure they're securely starpped in.

I know someone who lost a Swan 46 on a transatlantic delivery - one of the battery bank took the forehatch out.

 

[southchinasea]

Thanks for the feedback. 6 X 135AH is serious power supply, especially based on the 'equivalent' AH of 170 per unit. I assume this is not just domestics, but engine start and bow thruster? I have already asked for the extra battery so will end up with 3 x 135AH for domestic.
Cheers

 

[ccscott49]

You should have plenty of power for all things, remember the bow thruster is normally only on when the engine is running, so you can basically take that drain out of your total battery requirement calculations!

 

[southchinasea]

You are, of course, right and I had wondered, on other threads, why some appear to have separate battery for bow thrusters. I assumed people have concerns about long cable runs?

 

[ccscott49]

Thats exactly it, they run small cables to keep the battery charged, big cables, awkward and expensive, unless you buy welding cable!!

 

[HaraldS]

Well it does seem a lot, but when you make the calculation it really isn't. Here is what the balance looks like:
The 6 batteries are configured two in series to get 24V and 3 three of those sets.
They are all for service, engine and generator start is on an entirely separate 12V 115Ah Batterie.
Now I have put in semi-traction batteries, robust, don't spill and a thrid of the price of the gel batteries. I plan to put in gel-batteries later when I sail to places where you can't get replacement batteries easy. I assumed that for the first 4 years before that, the ragular batteries easily last. They are rated at 140Ah.
But these batteries should ideally be discharged only to about 60% and 50% is probably ok if a five year life is fine instead of 10.
Next problem is charging: I can charge from the main engine at sustained 80A (the alternator is rated for 100A, but gets too hot if you keep it at that level) and I can charge from the Generator or shore with 75A. Both have sophisticated three stage regulation.
You can charge a large battreie bank at that rate up to about 85%, but then you need to throttle back or the bateries would start gasing and would get too hot. hence, after that point charging gets increasingly slow. Since I don't want to run the gernerator forever, I'll stop charging at 85%.
Now that's also not good for the batteries and at the minimum you need to fully charge them about one out of eight times. If you have to motor for a longer time or if you hang out in a marina for a night, that happens automatically. If not you have to keep an eye on it, I do.
So for the average day I can use up from 85% down to say 55%, that 30% capacity. In may case about 130Ah at 24V. I can replenish that in about two hours of running the generator. So say I'm discharging for 22 hours and charging for 2 on a day where I don't use the engine. 130Ah in 22hrs is about a constant draw of 6 Amps. (144 Watts of constant draw).
In real life I seem to need more than that and my average 22 hrs consumption is more like 165Ah. Which means I'm regularly running my batteries down to 46%, I still think they will last the 4 years I intended them to last.
But you can see that this looks better with gel or AGM batteries.
Now, that's for a self contained ship that's hardly ever in a marina. If you are mostly connected, much less will do, but then you might have the odd day out where you really discharge very low which would kill a regular battery, not a gel battery. So I would say that also for mostly marina hook up, the gel is the right choice.
And the 3 times 130Ah at 12V isn't a whole lot, which means you will very likely end up with quite deep discharges.
Go for the gel.

 

[southchinasea]

Thanks. Useful stuff. Have already gone for the Gel AND extra battery.
Cheers