[scottorious]

Does anyone know of a safe method for cutting the packs down to make them into 12 volt unit? I really want to swap out my deep cycles in my boat and RV with some volt batteries but those forums seemingly just like to deal with tech that they fully understand. I don't want to convert the entire thing to 48 Volt so I'm looking to make 12 Volt batteries. Maybe someone knows of a better DC to DC converter than I do but I want more than the little golf cart units and I don't want to spend a crap load of money on a converter.

 

[john61ct]

People that understand DC House electrics on boats are understandably wary about safety issues. Most boat fires are electrical, and that's just using lead!

The only non-lead chemistry any sane insurance company might cover are fully packaged and BMS protected systems from Victron, Mastervolt Lithionics etc.

If you really put a DIY system together from standard LFP prismatics like CALB or GBS, usually 100-180AH cells, plus a solid OVD/LVD from OTS parts, maybe a surveyor could be found to sign off on it.

But packs of what NMC stripped from a salvage car, separated out from all the protective electronics?

That's a Science Project, IMO needs to be done on land.

But if you are willing to be a pioneer, please let us know how it goes!

BTW decent sized 48-12V converters are not that expensive, are you looking to run a windlass or just screens, reefer & galley appliances?

 

[scottorious]

Maybe I need to look into converters more. I really just want it to run navigation lights and electronics, house water pump and bilge pump and other assorted low power electronics. The biggest draw I would introduce at some point would be a DC refrigeration system. I have seen refrigeration systems that run on 24 volt but maybe one exists that runs on 48. I'll have to look into that more. I have a line on an affordable Volt battery so that got my brain juices flowing. It would be cheaper than buying the typical 6 volt bank of golf cart batteries for both my RV and sailboat.

 

[yewsuck]

Check out this thread. Yes, it is almost 6000 post long. It will show all the frustrations, success, and all the failures from going to a new chemistry. John61ct is a poster there on that thread as well. He knows what he is talking about. Here is the link.... http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-397.html

Even if you did put in the Volt battery, you would most likely have to change the inverter and charging sources. Most power system equipment over-charge, over-discharge lithium based batteries, or do not have a way for a BMS to safely turn off the charging/discharging source.

I am not saying it can not be done. It can be done. I have a off grid house with the more volatile car batteries. I have them in a separate shed away from my house. So if they do have a problem... It does not kill my family while they sleep. You will not find many people that will recommend you use the more volatile batteries in confined spaces. You will be taking chance with you or a loved ones life that YOUR wiring and YOUR safety devices work.

-YS

 

[pylon]

Yes, you can get out 12volts. I strongly recommend keeping the bolts and straps intact. To divide for 12v use, cut the "u" shaped tie between the vertical tabs at about 1/3" from the center. Use a multi-tool, and carefully cut only the depth of the connect, and a 1/4" wider either side. Cutting in the middle will not work as the tabs have connects under the plastic, and to0. close to the tab risks cutting into a cell. vacuum several times per cut and tape up the gaps around the cut to prevent shaving from getting into the battery. Apply silicone on the cut after through to insulate the ends of the cut. Perhaps I will post a photo in a couple of days.

 

[scottorious]

I would like to see that picture. Upon further review it seems like it might just make sense to leave the 48 volt modules intact and use an inverter that accepts 48 volts. Considering all the 48 volt modules have posts and would have intact BMS leads it might just be the way to go. As I learn more about these batteries and the lithium world I feel more comfortable breaking away from what is normal for the lead acid 12 volt world.

 

[john61ct]

Yes that would be easier, lots of 48V to 12V conversion devices out there, I would do that then you can use standard much cheaper inverters if needed.

Buy you def want good BMS protection on a boat using a chemistry at risk of thermal runaway.

LFP would lots safer

 

[scottorious]

Buy you def want good BMS protection on a boat using a chemistry at risk of thermal runaway.

I think You're right, I'm going to hold off on the boat for now. I can always bail out of my motorhome if things get a little warm but I should make sure I fully understand what I'm doing before I sail miles from shore with a fire in the making. The motorhome will be a great and hopefully dry place to really learn everything I need to know.

 

[john61ct]

Yay! You did have me worried there.

Just realize a small mobile living space requires more care too even on land.

IMO save your pennies for LFP prismatics, sometimes good deals come up on eBay.

 

[Yabert]

Yes, you can get out 12volts ...I will post a photo in a couple of days.

I'm (and probably others) interested to see this.

 

[Solarsail]

I would like to see that picture. Upon further review it seems like it might just make sense to leave the 48 volt modules intact and use an inverter that accepts 48 volts. Considering all the 48 volt modules have posts and would have intact BMS leads it might just be the way to go. As I learn more about these batteries and the lithium world I feel more comfortable breaking away from what is normal for the lead acid 12 volt world.

I would also recommend staying at 48V. There are for example hot water heaters at this voltage and this standard is gathering momentum. Propulsion for both EVs and EBs (electric boats) are now invariably 48V and are going up by a multiple of that to 96V, 144V, etc. I believe home DC standard fed by solar panels includes 48V. Most likely you will be able to find appliances at this voltage.

Note that 12s is a bit anemic for 48V and ideally you want to be 13s or 14s. For my projects, I am going 14s. http://www.diyelectriccar.com/forums/showthread.php/18650-13s10p-project-48v-x-34ah-188618.html

 

[Solarsail]

Buy you def want good BMS protection on a boat using a chemistry at risk of thermal runaway.

LFP would lots safer

In addition to the mandatory BMS, how about flooding the pack enclosure with seawater if a thermistor is triggered? Let's say two thermistors for every 1 kWh. If the pack is below waterline, no pump is needed. Of course pack must be in its own compartment, and an independent power source needed for the pump/valve.

 

[john61ct]

Actually I'm pretty sure shorting out all the cells with highly conductive seawater would have unintended consequences even if they weren't in the middle of a thermal runaway catastrophe.

Not to mention most boat owners are doing their best to keep that salty wet stuff on the **out** side of the hull.

 

[brian_]

Upon further review it seems like it might just make sense to leave the 48 volt modules intact and use an inverter that accepts 48 volts.

It does make sense that if most of the loads to be supported by the battery are 48 volt DC, or higher voltage AC for which a 48V-supplied inverter is available, then keeping the battery voltage up and current down is preferable. It seemed like most of the planned loads were 12 volt, though...

Inverters, converters, chargers... all of them can presumably be the same as used in residential solar installations, which now normally operate at higher than 12 volts if they are of any significant size. I'm no expert on residential solar, but 24 V and 48 V system voltages seem common, although I've seen some up to 72 volts.

 

[john61ct]

Everything get pricier at higher bank voltages except the wiring.

I would only go up from 24V if a huge consumer required it, e.g. aircon or propulsion.

Higher **panel** voltages are not relevant to output, that's between the MPPT SC and the bank.

 

[Duncan]

Why do you guys think that some chinese made cells are going to be any safer than a battery custom made to use in a car in a huge variety of conditions while being rattled about and have comparatively huge loads put into and taken out of it?

Something designed for a car is massively over specced for use as a battery bank in a boat!

As far as BMS's are concerned the ratio of batteries saved by BMS's to batteries killed by BMS's appears to be about 1:20

I would NOT have some low volume DIY BMS protecting my system - the Automotive ones would be OK

But otherwise you only need to know if a cell has failed - and a "Battbridge"
http://www.evdl.org/pages/battbridge.html
will do that for you

 

[Solarsail]

Actually I'm pretty sure shorting out all the cells with highly conductive seawater would have unintended consequences even if they weren't in the middle of a thermal runaway catastrophe.

Not to mention most boat owners are doing their best to keep that salty wet stuff on the **out** side of the hull.

Seawater's resistance is in the hundreds of ohms. You need milliohm shorts to generate any kind of power with any consequence. One would lose the electronics and cells maybe, but the fire will be contained. In fact the shorting at hundreds of ohms is exactly what you need to deplete the cells adjacent to the runaway cell. Note that the battery pack should be distributed in two or more locations throughout the boat anyways, and should not be all localized to one tight spot. I would be happy to have a compartment wet with seawater than to have a fire raging out of control.

 

[john61ct]

I'll just stick to LFP

 

[john61ct]

Why do you guys think that some chinese made cells are going to be any safer than a battery custom made to use in a car in a huge variety of conditions while being rattled about and have comparatively huge loads put into and taken out of it?

Something designed for a car is massively over specced for use as a battery bank in a boat!

As far as BMS's are concerned the ratio of batteries saved by BMS's to batteries killed by BMS's appears to be about 1:20

I would NOT have some low volume DIY BMS protecting my system - the Automotive ones would be OK

No one is talking about using the original vehicles BMS, they are only suitable for the EV parameters.

Chopping up salvaged auto packs then re-assembing into small lower voltage blocks is what you apparently don't realize you're talking about.

And doing that requires a much more stringent custom BMS in any case, and that's a much greater challenge than the simple LVD / OVD needed to protect standard prismatics.

The main point is, these non-LFP chemistries are inherently more dangerous.

The biggest buyers of LFP prismatics are military, in use cases much bouncier than civilian EVs.

China is irrelevant, it is the brand and sales channel that needs to be trustworthy.

I don't see that in most eBay sellers and junkyards myself.

 

[john61ct]

Just a reminder this topic is about storage for House loads, nothing to do with propulsion