Suggestions for portable 12V power

Started by ChugiakTinkerer, December 14, 2016, 02:02:12 PM

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

ChugiakTinkerer

All,

Somewhat tangential to house building but it does involve off-grid power.  I managed to kill a PowerSonic 12V 17amp-hour sealed battery the other day that was the heart of my portable 12V power supply.  The kit is essentially the battery and a SunForce 10 amp controller packed in a small Pelican case.  The resulting unit is just a bit larger than a six-pack of bottles and about four times heavier.

Anyhoo, I wasn't paying attention and hooked up the wrong charger and in short order had boiling acid.  The result is a bulging battery that is now slated for the city recycle center.  I thought I might take advantage of this opportunity to reconsider my portable power design and see what the pros and cons are to other options.  I figure my options are:
  1) replace with same battery
  2) stay with sealed lead acid but get a bigger one
  3) go old school and just use a 12V deep cycle
  4) go 21st century and use a lithium design

When I assembled this kit a few years ago my needs were limited to use of a CPAP machine while on float hunting trips.  I have 40 w of solar panels that work great in recharging the battery.  When the weather was really cold and cloudy I could get two nights use out of the battery.  I have also used this power pack at home when we had a power outage that lasted half a day.

Things have changed though, and my needs are a little different now.  My wife and I both have CPAP machines, and we are spending our time together at the property working on the cabin project.  I reckon I should bump up the capacity of the battery by at least 50%.  We do have generator power at the property to allow recharging in all weather, but I want to have a comfortable two nights use out of the battery for both of us.  Ideally my new power supply will be durable enough that I can pack it in the snowmobile sled for a weekend trip to the cabin, and have enough capacity for two nights use.

Does anyone have any thoughts or experiences with lithium chemistries for this use?  I really like the reduced weight these batteries offer, but admit to some trepidation regarding quality and safety.  Your comments and suggestions are welcome.

My cabin build thread: Alaskan remote 16x28 1.5 story

MountainDon

Elite Power is one seller of lithium ferrous phosphate (LiFePO4 or LFP) battery systems. They have been around a while. LFP is the safest of the lithium technologies. I like the GBS cells; the way they are made with covers for the terminals, 4 screw and plate connections instead of a single bolt.  Keep in mind that a lithium cell battery should include a BMS, battery management system.  That is because you can ruin a lithium cell quickly if over charged or if drawn down to too low a voltage. Depending upon how much maximum current draw is required the BMS can add considerably to the price.  Some folks have gone w/o a BMS, but I feel that is only for those who are going to be very involved in monitoring the state of charge much more closely than I would have to do.
Just because something has been done and has not failed, doesn't mean it is good design.


ChugiakTinkerer

Thanks MtnDon, is this the outfit?

http://elitepowersolutions.com/

Lack of a BMS (and a brain!) is what allowed me to destroy the SLA battery.  I think I should have a BMS, will investigate further.

Thanks!
My cabin build thread: Alaskan remote 16x28 1.5 story

MountainDon

Yes, that is it... I meant to include a link.   d*   Also these guys.

I think BMS is a good idea. The LFP have a long fairly flat discharge graph. There is a sudden up kick at full charge and a sudden down turn at the discharge end. Getting into those steep knee areas can be bad news. The BMS is supposed to keep you out of those areas. Also supposed to help balance the cells to keep their level of charge pretty much equal.

Just because something has been done and has not failed, doesn't mean it is good design.

ChugiakTinkerer

Here's a ruggedized turn-key portable power pack, pricey and twice the capacity I'm shooting for but very much like what my end goal is:

https://store.easpower.com/products/red-cell-12v-40ah-rugged-lithium-battery-module-lifepo4
My cabin build thread: Alaskan remote 16x28 1.5 story


ChugiakTinkerer

Elite Power has a kit that looks like what I need.  It doesn't have the sophisticated management system but it does have balancing and a low voltage disconnect.

http://elitepowersolutions.com/products/product_info.php?cPath=27_49&products_id=250

It's only $279 plus shipping.  Granted that's more than I spent on my SLA kit but it does a lot more.  And replacing a lead-acid battery every couple years is getting old.  And expensive.  Definitely something to consider, thanks again for the pointer.
My cabin build thread: Alaskan remote 16x28 1.5 story

MountainDon

One important detail. LFP's do not need to float charge; better if there is no float charge. The solar charge controller must have programmable set points.  I don't pretend to be an expert on the use of lithium with solar... I do know that my Midnight controller and the Outback are usable with LFP. 

The forum over at NAWS might be a better place or search and/or ask.  There are a few users of LFP over there.  LFP has been slow to be adopted by the off grid solar folks and by most vendors in the off grid field. Lots of caution because of the possibility of making expensive errors. But there are lots of successes too.
Just because something has been done and has not failed, doesn't mean it is good design.

MountainDon

Morningstar has some info that might be helpful. Of course it is oriented towards their charge controllers. 

http://www.morningstarcorp.com/morningstar-best-practices-battery-chemistry/
Just because something has been done and has not failed, doesn't mean it is good design.

Dave Sparks

Schneider Electric Solar has been one of the leaders with using LFP batteries. Their equipment has supported LFP for 10 years.
Their latest effort is in interfacing the Battery BMS with a realworld offgrid homes and grid tied battery based systems for peace of mind and safety.
The OP here may not need this level but a complete turnkey power system user might take a look.

http://cdn.solar.schneider-electric.com/wp-content/uploads/2015/04/using-lithium-ion-and-advanced-batteries-with-the-conext-series-of-inverterchargers-and-mppt-solar-charge-controllers-introduction.pdf
"we go where the power lines don't"


ChugiakTinkerer

Thanks for the pointers.  One thing I've learned is that LFP may not be the best choice in an extremely cold environment.  Still researching, but so far most LFP battery manufacturers say not to operate below -10 C.  Considering I encountered -16 F last winter I may need to be looking at lead-acid for a fixed battery installation.  I'm still exploring LFP for a portable power supply.
My cabin build thread: Alaskan remote 16x28 1.5 story

MountainDon

Re LFP, most of what I seem to recall states that charging should not be done when the LFP cells are below 32 F.  So if/when we switch I need to move the cells inside.  Our system does not need to stay active when we are absent so the cabin / batteries can drop to whatever during absences. We seldom get below zero temps.

Lead acid batteries can be used when very cold, but the available capacity drops. At -10 F you need about 50% more rated capacity to make up for that cold de-rating.  And then if you run the SOC down and the batteries sit through a freezing night you have the danger of the electrolyte freezing. There's a table of temperatures vs SOC in this Trojan document.

62% SOC freeze sat -16 F   ...  40% SOC freezes at +5 F
Just because something has been done and has not failed, doesn't mean it is good design.

Dave Sparks

Why can't this rush to very expensive Li-Ion batteries be put off until the price stabilizes in a few years. Just trickle charge a lead acid with a small panel until there are more solutions in cold environments? I know Outback will have something soon just as the work I am doing for Schneider. I do agree that I do not pay much attention to small solutions as most all I am involved with is large homes. No place better than here for the cabin folks!  [cool]
"we go where the power lines don't"

MountainDon

I am all for waiting Dave. I believe we can get another couple of years use out of our FLA's. The one advantage of LFP I like is the ir ability to sit un-used and not being charges for protracted lengths of time without being harmed quickly.   BTW, Merry Christmas!

Just because something has been done and has not failed, doesn't mean it is good design.

Dave Sparks

Right back at you Don! Have a very Merry Christmas!
For the OP the Kirkland 95AH 12V deep cycle was at my Costco for $85 or so. Hard to beat and a known safety solution!
"we go where the power lines don't"


ChugiakTinkerer

Quote from: Dave Sparks on December 22, 2016, 02:32:59 PM
Right back at you Don! Have a very Merry Christmas!
For the OP the Kirkland 95AH 12V deep cycle was at my Costco for $85 or so. Hard to beat and a known safety solution!
There's something to be said for KISS technology.  I might just go that route for now as it won't require anything new except for the battery.  If I switch over to LFP then I'm looking at a new solar charge controller as well.  Might as well put that off until I have a real cabin needing a permanent power installation.

Thanks all for the very helpful advice and may you and yours have a joyous Christmas and prosperous new year.
My cabin build thread: Alaskan remote 16x28 1.5 story

NathanS

A little unrelated, but I remember debating whether or not to buy a $15 LED for my desk light about 2 years ago. I was in Lowes the other day and they were selling 'em for about 89 cents.

Would have been smart to wait. It is a no brainer to put them in our house now though.

The cold temps are another tricky problem. Ventilating those golf cart batteries is tough when you know you've got -20 a few time a year.

I think the less your house needs electricity the better.

ChugiakTinkerer

By the time I get it built everything will be so efficient we'll probably be able to power the cabin with static electricity.  I'll put money into the wool socks for now.  ;)

My cabin build thread: Alaskan remote 16x28 1.5 story

Dave Sparks

Quote from: NathanS on December 22, 2016, 09:13:23 PM
A little unrelated, but I remember debating whether or not to buy a $15 LED for my desk light about 2 years ago. I was in Lowes the other day and they were selling 'em for about 89 cents.

Would have been smart to wait. It is a no brainer to put them in our house now though.

The cold temps are another tricky problem. Ventilating those golf cart batteries is tough when you know you've got -20 a few time a year.

I think the less your house needs electricity the better.

After some time doing this, I predict you will find a design that works if you want to keep doing it. It just takes money.
There are few people out there that want to live like their grandparents did 8)
"we go where the power lines don't"

wgiles

Lithium cells seem to be the coming thing, but I think that the lowest cost system, for now, is a deep cycle marine battery with a smart charger. The thing that I would try to stay away from is AGM batteries. Most of what we used to call Gel Cells are now AGM batteries. I have had numerous early failures of these cells, mostly the 17 AH variety. I have used these to power 600 watt true sine inverters for around ten years, but have switched to marine batteries or cheap U1 lawn tractor batteries. The lawn tractor batteries aren't made for this, but at around $30 each vs $150 or more for a U1 scooter battery, they have done well. The marine batteries aren't that expensive, if you catch them on sale, but they're just too heavy for my purposes.

flyingvan

My chemist friend always chuckles about the wait for decent batteries--claiming it goes all the way back to Benjamin Franklin.  His opinion is the fix is a simple one---all you have to do to develop a decent battery is change the periodic table.
Find what you love and let it kill you.