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BFL13

Victoria, BC

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Joined: 02/15/2006

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Posted: 05/04/20 09:45am Link  |  Quote  |  Print  |  Notify Moderator

Bruce's link here is what got me asking. Scroll down to the warning about "pre-balanced" packs and then down to the whole bit about cell balancing.

Perhaps Li is like Bismarck's sausages, where you don't want to know how they are made. Just enjoy them. [emoticon]

http://nordkyndesign.com/assembling-a-lithium-iron-phosphate-marine-house-bank/


1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
See Profile for House electronics set-up.
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas

Itinerant1

Itinerant

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Posted: 05/04/20 09:51am Link  |  Quote  |  Print  |  Notify Moderator

Whether you are doing a diy or a dropin they both have the same thing in initial setup and that's getting the cells balanced. With top balancing put the cells in series, if using a bench power supply set to 3.65v or whatever you want as your end voltage charge till zero amp, reassemble in parallel let cells self balance if need be and your good to go. Make your 12/24/48 volt pack.

My particular setting as mentioned before.
Charging Source: Solar_Magnum PT100, max 80a (.16c)
Charging Source: Magnum Inverter/ Charger, max 125a (.25c)
Absorb Voltage:14.1v (3.52 vpc)
Absorb Time: 10 minutes the least it can be set for, 6 minutes is usual amount of time it lasts.
Float Voltage: 13.6v (3.4 vpc)
BMS
Inverter LVD: 12.0v
Cell LVD: 2.8v (30 sec delay)
Cell HVD: 3.8v (3 sec delay)
Temperature: 32°F (30 sec delay), 150°f (30 sec delay)

April 2016 systems been on 24/ 7/ 365 with these settings.


12v 500ah (5,120Wh usable) , 20 cells_ 4s5p (GBS LFMP battery system). 8 CTI 160 watt panels (1,280 watts) 2s4p. Panels mounted flat on the roof. Magnum PT100 controller, Magnum 3012 hybrid inverter, ME-ARC 50. Installed 4/2016 been on 24/7/365

3 tons

NV.

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Posted: 05/05/20 02:08pm Link  |  Quote  |  Print  |  Notify Moderator

So I decided to let things run their natural course, so I switched on the PD 9245 and just let it do its thing and see what would happen at the SOC meter...Though not Li specific, the PD seemed to work out fairly well bringing the 200a/h LiFePO4 up to and holding at 14.2v, (steady light at charge wizard) with zero amperage going into the battery for a period of time, and LinkLite meter at 100% SOC (though followed by a fresh resynchronization), then with the PD dropping back to 13.6v (rapid blinking at charge wizard).

My conclusions are:

1) Though (in the interest of prolonging battery longevity) it may not be necessary to fully charge the battery (nor desirable to fully discharge), it seems somewhat unavoidable if the BMS is to be allowed an opportunity to achieve cell balancing...

2) Though the PD 9245 is not the latest wiz-bang LiFePO4 charger, the fact that it drops back to a13.6v float (float is not required nor harmful for Lithium) seems a far better option than PD’s latest Li offering which remains ON at 14.6v into perpetuity...

Just a few early conclusions....

3 tons

bdosborn

Colorado

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Posted: 05/05/20 05:44pm Link  |  Quote  |  Print  |  Notify Moderator

BFL13 wrote:

How do they know what to set the low voltage shut off at when it is not balanced at that end? I assume it is top-balanced.

They must be confident the cells are enough alike that one won't go too low.


That was another thing that I had to wrap my head around. I was under the impression that the cell voltages would vary widely but I've found that the difference between the highest and the lowest cells in my battery has always been at 0.008V or less. So the cells would have to be out of balance by a lot more than that before the voltage shut off would be inaccurate. I'm not running big loads and I have 6 amp cell balancers, which I'm assuming is the reason my cells have been staying so close in voltage.
Bruce


2010 6.5'X11' TTT - Boxcar
Custom Frame, Poptop, AC, Espar Diesel Furnace, HW Heater, Sink, Shower, 12V-120V, LED Lights, TV and XM Radio, DVD Player, 300W PV Panels, PD 9140 Charger, Tongue Box, Filon Exterior, 1000W Generator, Patient Wife
Boxcar Build


BFL13

Victoria, BC

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Posted: 05/06/20 08:42am Link  |  Quote  |  Print  |  Notify Moderator

http://liionbms.com/php/wp_soc_estimate.php

Looking at that paper again, and how the Charge Wizard works.

If the bank is at 70% and you do a recharge, AFAIK the PD by itself will not go into Boost, but remains at 13.6v. If the bank is more like 50% it will. But then it will drop to 13.6v after two or three hours depending on how long it takes to get to about 97% where it drops. (still not full)

If you use the Charge Wizard, no matter what the SOC you get four hours of 14.4v on the timer and then it drops to 13.6v. If not yet full, you hit the boost button and get another four hours. If you get to full after an hour into the second go, you can use the Charge Wizard to drop it to 13.6v yourself.

I don't have a PD, so if that is wrong, please correct that!

So the flat part of the Li voltage vs SOC I imagine would fool the PD so it never went into Boost even at 50%, but maybe at 25%? So you must use the Charge Wizard and have the fixed four hours at 14.4.

That might mean it stays at 14.4 three hours after it gets to full after one hour depending on the situation. So is that three hours too long? If it is, you must be there to manually drop it to 13.6 when the time is right. If it is not too long, you can leave it to drop by itself later.

Back to the paper and a new set-up IMO you should observe what happens closely taking notes and make a rough graph to find the point at the high end where the voltage spikes/drops and note the AH count.

First get the bank full at 14.x where amps flow has tapered to near zero and stop. Set the AH counter to zero. Start a load at the 20 hr rate (10 amps for a 200AH bank) and watch the voltage drop, taking note every few minutes for your graph and note the AH. When you see the voltage flatten out, you have enough info.

So now you know how many AH out of supposed 200 it took to get to where it flattens, so you know the SOC when it did that--might be 90% or whatever.

So what good is that info? You can use the AH counter from then on to get your SOC and never mind the voltage. You know that 20 AH is 10% so at 90% you are down 20AH. At the bottom where voltage drops off, it would be at say 180AH, so stay above that. You can tell how much you have left before you are as low as you dare to go.

Say you are using about 50AH a day as you see from experience. One morning you see the AH count is 140 down. So by tomorrow morning it will be about 190 down. Oops too far. So recharge today. Stop the gen when it gets back to 20 down just as voltage starts to spike ( about 90% SOC if that was the number when you did your testing)

On top-balancing each recharge--do you need to? I got the notion that you only need to be top-balanced when first building the bank to get your high voltage cut-off marker, but after that you don't care? Not clear on that. Li guys will know.

Scott&Julie

Maine

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Posted: 05/06/20 11:42am Link  |  Quote  |  Print  |  Notify Moderator

2oldman wrote:

These are Chinese products. The 2nd one says won't deliver to United States.

Bite the bullet and get a decent product instead of taking this kind of a chance. A quality lifepo should last many many years. You get what you pay for.

Cry once.


Thanks for the advice.

I agree with the cry once. Usually. But at $2400 for batteries and charger card it is not going to happen.

Scott

Scott&Julie

Maine

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Posted: 05/06/20 11:45am Link  |  Quote  |  Print  |  Notify Moderator

theoldwizard1 wrote:

Check out Will Powers' DIY Solar Power YouTube Channel.

He has reviewed several different brands of batteries. You can "build your own" without any special tools and save a lot compared to Battle Born.


Oh I know. I bought a kit for my bike, some of it took days other parts weeks.

Scott&Julie

Maine

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Posted: 05/06/20 11:56am Link  |  Quote  |  Print  |  Notify Moderator

Thanks for all the replies.

To those who suggested batteries, thanks. If you don't mind can you explain why you suggested them (except the $2200 ones)

To those discussing charging, you are scaring me away from lithium!


Scott

BFL13

Victoria, BC

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Posted: 05/06/20 12:30pm Link  |  Quote  |  Print  |  Notify Moderator

Any battery you get needs to be charged/maintained if it is to last.

There is perhaps a different risk/reward calculation with Li compared with Walmart 27DCs, but it is always scenario dependent.

For the OP, what would be the higher reward in your scenario to match the higher dollar risk if the battery bank is not maintained properly?

The guys here with Li have all said they did lots of research first for their own scenarios. Doesn't mean it would work for everyone's scenario; just as it doesn't mean it would not work for some scenarios.

pianotuna

Regina, SK, Canada

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Posted: 05/06/20 12:48pm Link  |  Quote  |  Print  |  Notify Moderator

Hell's bells I'd go LI in a flash if there were not the cold weather issue. The carbon based are able to get around that and still share the attribute of partial charging being acceptable. Now, if I had a champagne budget.......


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp hours of AGM in two battery banks 12 volt batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

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