As Betty is running a 24 volt habitation electrical system I will be assembling an eight cell battery, looked after by a 200 amp BMS.
At the moment I'm toying with what kind of links to use for making the battery. As the cells are prone to swell, more with aggressive use. (so I read) Some flexibility in the links would be good. Copper links with humps in would be the cheapest way to go, though not priced yet. Fabricated cable seem appealing, but 35mm sq is a hefty cable. Cable to buy, crimps and a crimping tool. I'm not going to solder that lot. Not so cheap if you have to buy everything in.
Other things to think about is do I heat them when cold?
How cold are they really going to get?
Would slowly charging them when cold warm them up, or just damage them.
Boxing them? Metal, wood or plastics ?
Prismatic cell compressing, is it really needed for gentle use. Or if you think you will be mistreating them, just buy more cells and be kinder?
I have software that can model stresses, but most of us know what will happen if you pressurise a rectangular box. Trying to prevent this deformation would require some hefty structure. Some studding and angle iron just won't do it.
At the moment I'm thinking about a pocketed box made from resin bonded ply, what a shame my wood working skills are shameful.
Pointed out to me by Wildebus for another project was seat heat pads, I wonder if their sizes would lend themselves to heating the bottom of the box? Two pads required in series as they would need to be 24 volts?
My take on this project is that there are easier options, but what the hell I like playing.
I haven’t attempted to build a battery but have fitted Lifepo4 so have a little real life experience. The battery’s I fitted do not have any heating fitted at all. My battery’s are fitted inside my van under one of the bench sofas along with most of the electrics, (previous owner had moved them inside instead of external locker directly below). I haven’t really been anywhere much below -12 since I changed to Lifepo4 but that of course is the external temperature, not inside the van.
I set my eberspacher to come on when the temperature gets to 10 degrees, more for my arthritis than the battery’s but serves a dual purpose as things in a Moho should
My Votronic MPPT takes into account temperature before passing charge to the battery’s, it has Lifepo4 settings. I believe me secondary Victronic MPPT also does this, I feel sure I read that but please correct me if I am wrong as not double checked.
My engine charging is all done through a Votronic B2B which again has Lifepo4 charge profiles and takes into account battery temperature.
I am rarely on EHU but have the facility to plug my generator into the EHU socket to run my two Victron mains chargers. These have Lifepo4 settings but I can’t remember if they are temperature aware or not. I wasn’t concerned about that as for me mains charging is a manual process so I can chose when I do it.
My battery’s are okay for normal charging and discharging down to 5 degrees C, below 5 degrees you can still charge but at reduced rate down to 0 degrees C. You can continue to discharge safely down to either minus 20 or 40 degrees C. These are battery temperatures not external hence why I am unsure of minimum, I am never likely to be in them alive.
On the rare occasion where I am not in the van, it’s reached a trigger temperature and I want to charge I would simply run my diesel heater for an hour or two to raise the internal and battery temperature.
So, rather long winded I know but my take is it depends entirely of where you intend locating your battery’s and what use you expect from you vehicle. If mine weren’t inside I would be looking at some method of keeping them warm. I have been running Lifepo4 for some time now through all seasons in the U.K. and have not encountered any problems at all with battery temperature.
While deciding this don’t forget the upper temperature as well, if you intend visiting hot country’s you may need to look at cooling options.
