Marine/Caravan batteries for solar setup? - Page 1
Forum section: electronics / general

author: paulca
author_rank: Super Contributor
timestamp: April 09, 2018, 02:39:44 pm
content: I stumbled onto the fact that large caravan/marine deep cycle lead acids are considerably cheaper than SLAs.I paid £55 for my 26Ah SLA which was cheap as it was old stock.However, for £85 I can get a 100Ah marine lead acid.I would assume as long as they are actually deep cycle batteries the only downside would be the potential for them to spill or leak and the maintenance required to keep them topped up twice a year?

author: fourtytwo42
author_rank: Super Contributor
timestamp: April 09, 2018, 05:49:14 pm
content: I wonder how deep they have to be cycled and how often to get the best life out of them, most batteries in my experience don't seem to like continious float duty much.

author: paulca
author_rank: Super Contributor
timestamp: April 09, 2018, 06:06:17 pm
content: My battery hardly ever sits at float voltage. If it's at float voltage I'm wasting solar power as I'm out at work all day. So I always run it charging things or moving energy to other batteries so if it's a sunny day while I'm at work I can capture it.So it spends it's life between 12V and rarely 13V.

author: Gregg
author_rank: Super Contributor
timestamp: April 10, 2018, 01:20:21 am
content: There are many advantages to wet deep cycle batteries.Pros:1. Individual cells can be checked for electrolyte specific gravity and give early warnings of possible failure. A refractometer is the easiest way to measure the electrolyte specific gravity with a single drop; just don’t get a really cheap one.2. Individual cell voltages can be measured even though the connections are covered by using some lead wire dipped into the electrolyte of a cell and compare the voltages from one terminal to each cell with a DMM.3. Sulfates that are the bane of lead acid batteries can fall to the bottom with proper charge procedures whereas glass mat and gel type batteries tend to retain the sulfates.4. With proper maintenance and diligence (don’t over discharge them) they will outlast sealed batteries (everything else being equal)5. They are cheaper to make, cheaper to buyCons:1. They are messy2. They need to be ventilated; hydrogen and oxygen are released when they are charged as well as acid vapors3. They need to be isolated from things that can’t handle acid vapors. If you put them in your tool shed, you will have the rustiest tools ever. Don’t even think of putting them near electronic equipment without forced ventilation and vapor isolation.4. They require maintenance. Distilled water needs to be added regularly. The more they are cycled, the more maintenance required.5. There is more space for explosive gasses to accumulate at the top of each cell and are slightly more prone to blow the tops off spreading acid everywhere.6. The battery terminals tend to corrode moreThings to consider:1. A quality charge controller is a lot less expensive than batteries2. Don’t discharge your batteries much further than 50% of their nameplate capacity. Adding strings of more batteries is cheaper in the long run than having to replace batteries.3. Use more than one string of batteries so that you can do maintenance on them in a disconnected stateI have a friend that has an off grid cabin powered by a Pelton wheel that produces 27V at 17A 24/7. He started out with two sets of golf cart batteries in the same shed as the inverter. It was a big mistake. I convinced him to build onto the shed a large battery room when I found some very large wet UPS cells. I rewired his whole system with a new inverter and charge controller. He hasn’t had any problems for 8 years, so far. I get free food and beer every time I visit, which I do on a regular basis to make sure he is doing battery maintenance.