Battery and 12 VDC power talk #3
19 January 2012 | Ft. Lauderdale, FL
The House Bank
The house bank is the heart of your boat's 12 volt system. It makes your life pleasant on board. It powers your cabin lights, feeds your sailing instruments, autopilot, anchor alarm with electricity, drives your entertainment center for music or movies, etc. It makes it possible to have a freezer and fridge on board. A cold beer tastes better than warm beer. To size a house bank, you add all the amps your 12 volt consumer will use in 24 hours together. They add up to a surprising number. Then add another 20% (for added future 12 VDC toys) and this total number multiply by two. This magnificent number should be the size in amps of your house bank.
You might ask: "Why multiply it by two?" Well, you don't want to discharge your house bank no more than 50% before recharging it, otherwise your charging equipment has to work overtime and this could mean generator noise for many hours on some boats. I'd say, using AGM style batteries to build a house bank on boats or RV's is today's the best choice. AGM batteries can be discharged down to 20% of their capacity without recharge them, but I don't recommend that. They are truly maintenance free and don't vent out hydrogen gas while being charged. They are considered to be extremely safe batteries. Wet cell deep cycle batteries are still common in house bank application, like on "Diesel Duck", but giving more and more way to AGMs.
On Diesel Duck the house bank, like I mentioned in a previous write-up, is a wet cell 950 amp deep cycle battery bank consisting of 2 pairs of Trojan L16H-AC batteries each 435 amp and one Trojan 24 TMX 80 amp battery. The L16H are 6 volt batteries and two in series become 12 volt. The L16H are floor sweeper batteries and are designed for deep discharge. To counteract the hydrogen gas release during the charging process, I fitted or replaced the original vent caps with Hydrocaps Catalyst battery caps from the Hydrocap Corp in Miami, Florida. Tel. 305 696-2504. These caps turn the hydrogen gas into water. Recently, we noticed that the L16H size batteries are now starting to being manufactured as AGM type batteries. So the next time, when we have to exchange the L16H batteries, we will replace the deep cycle wet batteries with AGM batteries. I met a boat owner with a Manta Cat in Santa Martha, Colombia who told me that his house bank of AGM batteries was 13 years old and still fine without giving him a battery trouble headache.
As indicated in the previous #2 write-up, a boat with fully charged AGM batteries on bord can be left in storage for quite a time. The AGM batteries lose only 2 - 3% of the charge in a month. This means you can leave your boat in Trinidad on the hard during the Atlantic Hurricane Season. Once you get back to the boat in December, the batteries still have an almost full charge. You don't have to worry if the charging cord is still plugged into your boat or some bozo has unplugged it down in Trinidad while you are home in Canada or the USA. Even if he did it, the charge level is still in a okay bracket when you return to your boat to resume cruising in the lovely Caribbean islands. For wet cell deep cycle batteries this could mean a death sentence!
The future house bank in a few years to come will be built out of lithium ion Batteries. They are already very common in consumer electronics, but for now, a 12 VDC marine lithium ion 330 amp battery from Mastervolt costs as little as $ 8360.10 incl. free shipping in continental USA. Cheers!
In the next write-up I'll talk about battery chargers and charging.