LiFeYPo4 questions

[Sunking]

We were still at 52.2 V for the 16 cell suite when we dropped to 55% DOD.

Reed I must be missing something and if so I apologize. I assume we are talking about LiPo chemistry. 52.2 volts on a 16S LiPo pack is 3.27 volts per cell. On a LiPo that correlates to a DOD of more than 100% or less than 0% SOC. 55% SOC is about 3.85 volts or 61.6 volts on a 16 S pack. I run a 16S pack on my racing golf cart.

So what am I missing here?

[reed cundiff]

We do have a BMS and I check the monitor several times each day (primarily when we wake up). We have never gone below 52 V for the suite or 3.25 V per cell. We were still at 52.2 V for the 16 cell suite when we dropped to 55% DOD. It is full overcast with slight rain on coast of Oregon just north of Rockaway Beach and we were charging at around 700 W. Fully charged by 11 am.
Reed and Elaine.

[Sunking]

3.1v per cell sounds reasonable, although for me I prefer not to go below 3.15v (12.6v for a nominal 12v battery).

Are we talking LiPo battery without BMS? If so I would not dare go below 3.2 volts without BMS. Eventually a cell is going to become unbalanced and low voltage. When that happens and it locks itself out, you are in big trouble. So for a 4S LiPo I would never dare to go below 12.8.

[PNjunction]

3.1v per cell sounds reasonable, although for me I prefer not to go below 3.15v (12.6v for a nominal 12v battery). The reason being is that once you start going below 3.2v (12.8v for 12v batt), you are entering the discharge knee, and while shallow excursions into it aren't necessarily bad, the recharge needs to be slow until the battery reaches 12.8v whereupon you can apply a normal charge current. Then again, with solar, you may not be applying much more over 0.1C anyway.

I shudder when I see guys reading the spec sheets and thinking that going as low as 2.5v is ok as an LVD limit. Maybe once or twice, but not as a practical limit! Kind of like thinking that 10.75v for lead acid is ok to take your battery down to all the time.

I think you'll be just fine.

Re the BMW - just like a Harley, it too is indescribable until you ride one with the crisp snickety-snack of the precision gearing, throttle feel etc. A different world, but just as invogorating! Hint - we can put lifepo4 under the seats of these as well, with Antigravity, Shorai, EarthX and the like for SLI duty...

[reed cundiff]

PNjunction - We seldom go below 30% DOD but we just wanted to see how far we could go but I was satisfied with 55% DOD and 52.1V (with 54.4 V system). Son put a sheet next to monitors that we should not below 3.1 V per cell and 49.1 V for suite.

I rode BMWs for a few years and about 100,000 miles. That was 35 years ago (uh, been married for 35 years)\
Reed

[PNjunction]

Wow - beautiful!

You bring up a point about lifepo4 with their ability to go down to 80% DOD - don't be tempted to design your solar system around that 80% DOD percentage! Stick to 50% or so like with any chemistry, and you'll have a nice reserve for times like this.

Lifepo4 is like riding a Harley - until you do, you can never truly describe the feeling.

[reed cundiff]

the big woods.jpg
We contacted a National Park Service CG about possible solar friendly sites on the Olympic Peninsula. The gracious lady gently chided me "Sir, this is a rain forest, there are no spots where solar panels will be of much use!" We wound up staying at Klawhoya National Forest CG for those six days. We checked our solar/battery monitoring system several times each day. At the end of six days were were down 55% DOD and had used the inverter every day for microwave, charging computers and watching Mystery Theater on DVD. We could have lasted another 4 days before we reached 80% DOD. The attached photo shows our site. It was most green and beautiful.
Reed andElaine

[PNjunction]

The misinformation makes for good headlines and newsbytes. It doesn't have to be accurate any more, sadly.

Funny you should bring up the Manzanita. Instead of hashing it all out here, I just plainly do without a balancing system after testing, but understand those that feel the need.

I recently tested out a 20ah and 40ah 4S block of GBS batteries, and came to my own conclusions. It might be interesting if you can take a week off work to read it.

http://forum.solar-electric.com/showthread.php?23898-GBS-LiFePo4-20-and-40ah-batts

I just finished my discharge testing and came to some enlightening conclusions. You may not feel the same way, but is just to let you know where I'm at in this stage of the game because I truly feel I could build a larger Kw system with at least some understanding now...

[reed cundiff]

As others have noted on this thread, the LFP batteries and BMS that have been developed for Electric cars/motorcycles etc. Our son has contacted Mazanita to see if they could adapt the BMS for RV/remote site usage. Have not heard how this has gone.
Reeed

[reed cundiff]

PN thanks for your useful rep!ies. We usually leave the inverter on full time all night (we have the battery suite so why not). This is about a 50 W phantom and we are down -1500 W at dawn so we are about 15 to 18% DOD. May jusr leave the fa
Fridge on electric overnight as we are then only down 30%. Am still in PbS frame of mind after a year with LFP but am slowly ac spring 80% instead of 40% DOD. Am following so similar discussions at Road Net and most folks are clueless there, many seem to think that a PbS has 100% DOD and do not understand the weight/volume advantages for a trailer/caravan. Every third or fourth comment brings up the fire danger if lithium coba!t.

[PNjunction]

There were remarks earlier on this thread about problems in keeping LFP at to high a charge. Should we discharge them more fully.
Reed and Elaine

Sorry about that Reed - forgot to mention that from a user I trust, to avoid a mini-cycle, it is best to discharge no less than 20% SOC. I'll leave that to your monitoring to figure out.

If you have plenty of capacity, I see no need to charge higher than about 3.5v per cell, often less at 3.45v per cell. I don't get too hung up over "end amps" like C/20 since I have way more capacity than needed, and you don't NEED to charge LiFePo4 up to full each and every time. In fact, 3.45v will get you very close to full anyway, barring some manufacturing differences.

[Sunking]

Awesome! Whether you do tppl pure lead with that, or perhaps even LiFePo4 for your, um, niche project, be sure to look at what these guys who do:

http://www.wheelchairdriver.com/

and

http://www.wheelchairdriver.com/board/viewforum.php?f=2&sid=0851abdf13412bbbfa08da9d102743cd

They can do 40-50 drags. Or 4x4. Definitely related, just a different form factor.

To get the range and speed no choice but LFP. Pb just does not have either the Specific Energy, or Energy Density to fit in the compartment and still be lite enough to cut the mustard. I hang out on a DIY EV forum where there are a lot of industry pros and it is pretty easy to do what I want using off the shelf products for the DIY EV market. Lot of motors, controllers, and batteries around. Only issue is the suspension and brakes. Fortunately there are a lot of golf Cart custom shops that do exactly what I want and have the parts to make it happen. If all I wanted is 30 mph is extremely easy using OEM parts dirt cheap. Going 50 for 20 miles is easy and cheap. Going 50 safely is a bit expensive in a cart designed to only go 20. All the suspension and braking has to be modified. Basically hydraulic disc breaks, and independent suspension vs solid rear axle and drum breaks carts come with.

[PNjunction]

Real easy to tell when that time comes when you see the major manufactures offering charge controllers with BMS to work on LFP or like batteries.

You'll be waiting forever for that. They've known about it for about 15 years, but from a business standpoint, as soon as they step out the door they'd be hit with patent-trolls, litigation and warrantee claims from duffers, not to mention just seeing no need to disturb the existing stock of Pb inventory. They WANT you to think that LiFePo4 is only for niche markets, lab-rats, or perhaps the endless 5-years-from-now wait. We're STILL waiting for Concord to come forward with theirs, and if anyone was to produce a LiFePo4 that I could get my hands on, it would be from them. The problem is that there is no indication that they will actually bring it to the consumer market. I'm moving forward. I can take my tinfoil conspiracy hat off now.

Having said that I just bought a used Golf Cart to make me another Racing Golf Cart. This one will be different and built to go 40 to 50 mph rather than 0 to 30 in a second. Looking to do a 90 volt system using a Brushless PM motor. Intend to use 96 volt 100 to 150 AH LFP pack on a 500 amp Electronic Speed Controller.

Awesome! Whether you do tppl pure lead with that, or perhaps even LiFePo4 for your, um, niche project, be sure to look at what these guys who do:

http://www.wheelchairdriver.com/

and

http://www.wheelchairdriver.com/board/viewforum.php?f=2&sid=0851abdf13412bbbfa08da9d102743cd

They can do 40-50 drags. Or 4x4. Definitely related, just a different form factor.

[Sunking]

In all seriousness, YOU are the last person I would BS or try to persuade with fan-boy / green / unsafe diy enthusiasm.

I know you were not trying to put one over on me, and I hope I did not come across making you think I thought you were. I have no problem with you or your experimenting. It can be a fun hobby while educational at the same time. All I am saying is RE i snot driving Lithium battery development, it is EV driving that cart. RE will just be a side beneficiary of the EV market. Real easy to tell when that time comes when you see the major manufactures offering charge controllers with BMS to work on LFP or like batteries.

Do I have to drop-ship a 4S set of CALB's to you? Of all people, I really think you'd enjoy it.

LOL. Only thing I use LFP for is RC planes and my racing Golf Cart I sold before moving. Still have my NEV though.

Having said that I just bought a used Golf Cart to make me another Racing Golf Cart. This one will be different and built to go 40 to 50 mph rather than 0 to 30 in a second. Looking to do a 90 volt system using a Brushless PM motor. Intend to use 96 volt 100 to 150 AH LFP pack on a 500 amp Electronic Speed Controller. Down here in Panama I can get away with driving one around town. I just need it to go fast enough as not to get ran over, and climb the hills with at least a 20 mile range. Going to have to re-do the suspension and braking system to be able to handle the higher speeds safely.

[PNjunction]

Until there are controllers/BMS made for RE I do not see it going anywhere fast. Right now as it stands lithium cannot compete in the RE sector. I think that will change sometime in the future, but still a good ways off in the future.

There are a few. Genasun / Mastervolt at the top. But how about something more down to earth:

http://minibms.mybigcommerce.com/products/HousePower-BMS.html

or this:

http://www.elitepowersolutions.com/

These are just two.

That being said, I don't need the insurance as I have my own hvc (charger / controller appropriately set), lvc (proper planning, monitoring, and worst-case, inverter shutoff), and balancing (initial balance with small resistive load after a full charge to bring all cells down to 3.45-3.5v) - they stay that way since I'm not doing high-C current, which in this case high-c means 1C or higher!

Imagine if you powered a handheld transistor radio from your RC packs. (different chemistry of course). Cost? My exploratory 20ah bank (16ah usable down to 80% DOD) costs just about the same or even a little less than a roughly equivalent pure-lead 38ah Optima D51 Yellowtop (19ah usable down to 50% DOD). And that's just cost alone, but when you factor in twice the cycle life, it puts it ahead. Then there are the other characteristics that battery-geeks like us dig, like minimal Peukert yada yada.

In all seriousness, YOU are the last person I would BS or try to persuade with fan-boy / green / unsafe diy enthusiasm. While these cells won't do the cycles and rates you are talking about, how about HALF of what you mentioned? You can if you don't take them to the extremes. Default for these prismatics is 2K cycles down to 80% DOD, at .5C. Even more if you treat them like we normally do in a house-bank situation where we do FAR less.

Do I have to drop-ship a 4S set of CALB's to you? Of all people, I really think you'd enjoy it.