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Old 13-03-2013, 10:05   #2356
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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I just read Jack Rickard's latest blog post. Skip the first part about Brian, unless you follow it often. But later he delves into both LiFePO4, plus an analysis of the Boeing problem like only Jack can. Good reading....:this is a guy with the most practical experience with LiFePO4 in the US that is willing to talk about it. See:

If I Only Had a Brain... and 12lbs of Potatoes in a 10 lb Sack - EVTV Motor Verks
Interesting read. Seems to mention my concern about banding these batteries. If you limit the case expansion then the metals in side might distort internally possible breaking through some insulation layers after a time. Resulting in a possible short and thermal runaway. I'm sticking with my AGM's and Gel's until some of these issues along with the charging issues get sorted out. Then there are the supply issues. I don't want to be cruising down the ICW and have to wait weeks for a replacement cell. I think we are still a few years away from these being available at the local West Marine. Of course I said that five years ago too.
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Old 13-03-2013, 10:07   #2357
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Lagoon4us---I agree with regard to the pedantic. I really would rather discuss topics of more general interest.

On that note, I discovered an interesting $17 DC solid state relay at Future Electronics: HFS33/D-50D80M | HFS33 Series 80 A 50 V DC Control Solid State Relay Panel Mount | HONGFA RELAYS - Future Electronics It is rated 80A at 50V and has a very low 8-millohm on-state resistance. Don't know anything about the company Hongfa, but the specs are comparable to a $100 Crydom model at a sixth the price.
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Old 13-03-2013, 10:09   #2358
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Cheers Bob, i mean it with respect totally but we have to get on with it, my batteries arrive soon, the solar is in place the cables arrive with crimpers and crimps on friday....... There's 750 watts wanting to get moving!!!
I went back to your post #2238 when you mentioned the only cells you could find where 400 a-hr at $2900 for 4 from China. Is that the route you went or did you grab the last of the 700 a-hr cells from Balqon for $2240 for 4?
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Old 13-03-2013, 10:29   #2359
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Capt Mike,

As I've said before, you and LiFePO4 are a good match. Electric propulsion at 48 volts, combined with a 48 volt inverter would be sweet. Your range without firing up the Honda would be at least 4 times what it is now, not to mention using a induction hot plate for cooking.
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Old 13-03-2013, 11:09   #2360
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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It is my belief that these cells are failing because they are being slowly and cumulatively overcharged repeatedly. At some point, they are sufficiently mechanically swollen and the SEI is sufficiently damaged to allow recombination and a thermal event. LiCoO2 cathodes are peculiarly susceptible to this as an ignition source.

The BMS is not the problem. The Battery CHarging Unit is not the problem. The cells are not the problem. The container is not the problem. The problem is they are overcharging my cells BY DESIGN in routine operation, and then they are going to blame the cells. I am deeply offended.
This is his conclusion, however its not supported by any data as that data isnt there in the report so its a theoretical conclusion based on hypothetical data

So his conclusions have nothing to do with banding.

I dont see what he bases his conclusions on. Ive not seen any evidence that repeat idly recharging from a lower voltage to the designated voltage results in overcharging. Yes his is correct is that when a Li charge cycle completes at the designated voltage cutoff. the correct procedure is to terminate the charge until a certain time later, and when the voltage has reduced then a mini-cycle can be restarted

There is no doubt ( and Im currently in this design conundrum myself in a current project) that repeated top up charging in situations where LIs are acting as merely backup is problematic. Some commentators believe recharging should only take place when the voltage falls significantly other suggest that it can begin at round 85-90% of the nominal battery voltage

This has issues for boats , as the current tendency is to leave charge sources in circuit all the time, hence the concerns of overcharging as a result of many mini cycles.

Li seems to be best in a charge , use( discharge) environment, like portable equipment. It would be useful to see more feedback on situations where Li is being used as in effect a battery backup.

This does have a major consequence in boats, which are subject to lots of mini cycles

dave
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Old 13-03-2013, 11:23   #2361

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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

"its a theoretical conclusion based on hypothetical data "
May I be so harsh as to suggest, it isn't even hypothetical data, it is outright mythological data?

And as any sailor knows, you can easily stuff twelve pounds in a ten pound sack. that's what a blivet is, a "sack" that can hold more than it can hold. Fuel blivets and Nauta tanks being the most common examples.

How many years did it take before anyone figured out that the Hindenberg didn't explode because of hydrogen? And that the Nazis knew it was a thermite fire, shortly after the event, and simply buried that information for 60? years?

Not that I'm suggesting anyone is hiding anything, just that even a well-motivated investigation can miss something terribly simple and obvious, for a very long time.

Heck, folks who make integrated circuits know that they're damaged by cosmic rays all the time. IBM used to say that the average server took four memory failures from cosmic rays every year. So, server, battery, same size box, but the battery is way up there and exposed to more radiation...Has anyone tried bombarding the battery with ionizing radiation, to see if that can cause a meltdown? Not that I've heard mentioned. A simple environmental factor, that isn't replicated on ground tests.

Now, that's hypothetical. Not mythological.
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Old 13-03-2013, 11:32   #2362
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Bob, I went for the 4 x 400 amp direct from China ..
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Old 13-03-2013, 11:33   #2363
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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This is his conclusion, however its not supported by any data as that data isnt there in the report so its a theoretical conclusion based on hypothetical data

So his conclusions have nothing to do with banding.

I dont see what he bases his conclusions on. Ive not seen any evidence that repeat idly recharging from a lower voltage to the designated voltage results in overcharging. Yes his is correct is that when a Li charge cycle completes at the designated voltage cutoff. the correct procedure is to terminate the charge until a certain time later, and when the voltage has reduced then a mini-cycle can be restarted

There is no doubt ( and Im currently in this design conundrum myself in a current project) that repeated top up charging in situations where LIs are acting as merely backup is problematic. Some commentators believe recharging should only take place when the voltage falls significantly other suggest that it can begin at round 85-90% of the nominal battery voltage

This has issues for boats , as the current tendency is to leave charge sources in circuit all the time, hence the concerns of overcharging as a result of many mini cycles.

Li seems to be best in a charge , use( discharge) environment, like portable equipment. It would be useful to see more feedback on situations where Li is being used as in effect a battery backup.

This does have a major consequence in boats, which are subject to lots of mini cycles

dave
Dave does Solar therefore more suit with the natural cycle day/night?
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Old 13-03-2013, 11:36   #2364
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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How many years did it take before anyone figured out that the Hindenberg didn't explode because of hydrogen? And that the Nazis knew it was a thermite fire, shortly after the event, and simply buried that information for 60? years?

well no, Mythbusters put paid to that theory. If there was enough Thermite , Hindenburg would have been too heavy

Dave
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Old 13-03-2013, 11:38   #2365
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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well no, Mythbusters put paid to that theory. If there was enough Thermite , Hindenburg would have been too heavy

Dave
LOL... some people must hate the Mythbusters

I love them BTW
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Old 13-03-2013, 11:38   #2366
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Dave does Solar therefore more suit with the natural cycle day/night?

Possibly , The main discussion/arguments are around repeatedly restarting charging on a Li battery that while the voltage has drifted down to the restart point, has not in any reality suffered any significant discharge. So for example a battery on a boat , thats locked up but still has solar connected.

I suspect that we need to look at amp counting as well as voltage levels to restart charging.!


The problem is what voltage to pick to resume charging, below the nominal voltage and you could have left the battery discharge a long way with a significant recharge time , above the nominal voltage and certain critics will tell you that even though you are below the ,max knee voltage the possibility of overcharging can occur on repeated such "mini cycles"

Personally Ive not seen how this happen, on reconnecting the charge cycle , on a practically full battery , the voltage very rapidly returns to the charge cutoff point. Ive not seen any conclusive evidence that the time taking from the recharge point to the cutoff point on a full cell is injurious , I have seen scientific comment that such mini cycles use up battery life.

Any feedback from others . I must take it onto a few Li-ion sites.

Where you to agree with Jack ascertain, it would mean that LI has completely unsuitable for battery backup situations, such as starting batteries or any battery that spends a lot of its time fully charged or nearly so.



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Old 13-03-2013, 11:43   #2367
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

<i>A simple environmental factor, that isn't replicated on ground tests.</i>

I will take issue with calling the space and upper atmosphere radiation environment "simple"...

Variants of lithium ion are flying on orbit, those are being well dosed and no reported failures (we've had a number of little notices about what needs to be done for nickel hydrogen batteries to get replaced with lithiums at work, lots of practical issues to work through still, particularly for retrofitting older designs but I'm just the ME not EE so a bit of it goes over my head). There are also a number of ground test facilities designed to expose aerospace equipment to various forms of radiation, Boeing would know about these and make use of them if they thought it prudent. Being internal to the airframe means that the radiation exposure is cut down somewhat, particularly for the more low energy species. I am also not aware of a mechanism that would make me think they could produce a catastrophic failure from radiation, but I can't rule it out either.

Unrelatedly, my order from EVelectronics came in, 4x 100Ah Sinopolys. They are the old case type, all gridded plastic, not that funky looking swirl in the center of the flat faces. Only complaint was that the box could have used some more cardboard on the bottom, it was pretty flimsy and the styrofoam was broken up underneath by the time I got them. Also, remember that they are hazmat shipped, so don't send them to your house and hope you can just leave a signature... d'oh!

Next step sounds like I need to go find a multimeter and power supply and try to bring them up to the top of the voltage curve...

Andy
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Old 13-03-2013, 13:19   #2368
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Bob, I went for the 4 x 400 amp direct from China ..
Great. When you get them tell us the date stamps. I'll bet you will have the newest cells of any of us. Congrats.
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Old 13-03-2013, 13:46   #2369
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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And that's an overcomplication. The internal resistance of a cell is a very basic quantity, which can be easily measured by any patient sailor with a multimeter. Constantly insinuating that it constantly varies does not help to promote its understanding.




I don't need an oscilloscope to understand what happens. I hate to break it to you again, but it's just Ohm's Law.
It's not an over-complication at all. Goboatingnow has it right. The source impedance model of any cell chemistry and especially lithium can be very complex and dynamic. Not easy to predict as the model changes with charge state, temperature, and recent load history (recent as in minutes). I've been designing systems using various battery chemistry for over 25 years for medical and aviation applications (admittedly not as long as GoBoatingNow ). No one doing this makes those kinds of oversimplifications for long. I suggest that you *DO* need an o'scope to really understand what happens. Thankfully, very few of us actually need to "really understand" what is happening and simpler models may be used with caveats. I also agree that Mainsail's testing is very applicable as it tests the real components as would be used on our boats and is a data point as to what would be acceptable OCP methods. The models are a starting point, but testing the actual hardware is where the rubber meets the road.
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Old 13-03-2013, 14:06   #2370
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This is his conclusion, however its not supported by any data as that data isnt there in the report so its a theoretical conclusion based on hypothetical data

So his conclusions have nothing to do with banding.

I dont see what he bases his conclusions on. Ive not seen any evidence that repeat idly recharging from a lower voltage to the designated voltage results in overcharging. Yes his is correct is that when a Li charge cycle completes at the designated voltage cutoff. the correct procedure is to terminate the charge until a certain time later, and when the voltage has reduced then a mini-cycle can be restarted

There is no doubt ( and Im currently in this design conundrum myself in a current project) that repeated top up charging in situations where LIs are acting as merely backup is problematic. Some commentators believe recharging should only take place when the voltage falls significantly other suggest that it can begin at round 85-90% of the nominal battery voltage

This has issues for boats , as the current tendency is to leave charge sources in circuit all the time, hence the concerns of overcharging as a result of many mini cycles.

Li seems to be best in a charge , use( discharge) environment, like portable equipment. It would be useful to see more feedback on situations where Li is being used as in effect a battery backup.

This does have a major consequence in boats, which are subject to lots of mini cycles

dave
What he is saying, the way I read it, is that each chemistry has a "full" voltage. Trickle charging by maintaining a constant voltage above that level overcharges the battery, and the effects are cumulative. I think he quoted 3.38V for LiFePO4. He does not say "floating" below that is OK, but I admit to inferring he would think that's OK.
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