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Old 12-18-2018, 01:12 PM   #1
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Swapping Out Trojan T105 House Bank for FireFly L15+ Bank

I'm swapping out my existing 12v house bank (six Trojan GC2s in 3P2S) for six FireFly L15+s in either (12v) 6S2P or 2P6S configuration.

Background: FF L15+s are interesting in that each battery consists of 2 x 450Ah/2v cells that can be set up in either series or parallel configuration. This allows using the same six L15+s to set up either a 12v/900Ah or 24v/450Ah bank.

I'm looking for input here first on which 12v FF configuration (6S2P or 2P6S) to set up before I confirm with the factory, Schwab, etc. The 6S2P (see drawing of Old Bank and New Bank together) is much neater than 2P6S config (see Alternate configuration drawing), but maybe the 2P6S is better for some reason?

The batteries must go in the box as shown for the old T105 and new FF L15+ footprints to match.
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Old 12-18-2018, 04:23 PM   #2
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Quote:
Originally Posted by Wil View Post
I'm swapping out my existing 12v house bank (six Trojan GC2s in 3P2S) for six FireFly L15+s in either (12v) 6S2P or 2P6S configuration.

Background: FF L15+s are interesting in that each battery consists of 2 x 450Ah/2v cells that can be set up in either series or parallel configuration. This allows using the same six L15+s to set up either a 12v/900Ah or 24v/450Ah bank.

I'm looking for input here first on which 12v FF configuration (6S2P or 2P6S) to set up before I confirm with the factory, Schwab, etc. The 6S2P (see drawing of Old Bank and New Bank together) is much neater than 2P6S config (see Alternate configuration drawing), but maybe the 2P6S is better for some reason?

The batteries must go in the box as shown for the old T105 and new FF L15+ footprints to match.
Great question. I'll be doing this myself at some point so I will watch with interest what the experts have to say. If we're lucky MainSail might respond.
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Old 12-19-2018, 06:57 AM   #3
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Interesting question!
My only observation so far is that the 3rd diagram will have all the amperage passing through jumped pairs of cells. This would necessitate significant larger jumper cables. In a relatively low draw situation, this may not be a problem. If you plan to use the bank to power an inverter, things can get interesting. My Magnum Energy 2812 inverter can pull a maximum of 300 amps 12 VDC. From my bank to the distribution panel is 4/0 wire! For your bank the jumpers won't need to be that large due to the short lengths, but they will need to be larger than the ones in the second configuration. I would make a determination of maximum amp draw and wire size before determining battery configuration.

Ted
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Old 12-19-2018, 04:39 PM   #4
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OC, hm, yes the third diagram (2P6S) may need larger jumpers between each battery, due to the two cells in parallel within each battery--is that what you said? I can see that logic if so.

That would lead me to the second diagram (6S2P) as being better in that respect, as the series current through each of the two 6 cell/three battery banks will be equal. And the current draw for the house is split between those two 6S (diagram 2) banks. So the cables at the point where the two banks come together will need to carry the whole house load, but each bank will only need to carry half the house load. Leaning more towards diagram 2 now....

I have only a 1500W inverter right now, but looking at upgrading to a 3KW inverter down the road. I'd like to get away from propane, one way to do that is an Induction stove . The other loads (fridge, pumps, radio, lights, etc.) are nominal.

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Interesting question!
My only observation so far is that the 3rd diagram will have all the amperage passing through jumped pairs of cells. This would necessitate significant larger jumper cables. In a relatively low draw situation, this may not be a problem. If you plan to use the bank to power an inverter, things can get interesting. My Magnum Energy 2812 inverter can pull a maximum of 300 amps 12 VDC. From my bank to the distribution panel is 4/0 wire! For your bank the jumpers won't need to be that large due to the short lengths, but they will need to be larger than the ones in the second configuration. I would make a determination of maximum amp draw and wire size before determining battery configuration.

Ted
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Old 12-19-2018, 07:40 PM   #5
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That's basically what I'm saying. With each pair of cells that are wired in parallel, those jumpers probably don't need to be much heavier. The jumpers that go from one pair of paralleled cells to the next will carry twice the amperage, so they will need to be significantly heavier.

IMO (which is worth what you paid for it), I favor the 2nd diagram. If for some reason you have a battery or cell failure, it would be fairly easy to disconnect one of the two strings, and still have half the bank useable.

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Old 12-20-2018, 06:32 AM   #6
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"I would make a determination of maximum amp draw and wire size before determining battery configuration."

Beside co$t there is no downside to large wires.

Just install tinned , pro crimped 4/0 and never worry.
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Old 12-20-2018, 06:59 AM   #7
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First, I think you have your existing bank labeled incorrectly. Itís shown as 2S3P. But not a big deal.

As for the new arrangement, Iíve heard arguments both ways. The same is true for anchors and wet vs dry exhaust. Iíd pick based on fewest cables and connection points, and as drawn that would appear to be the 6S2P configuration.
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Old 12-20-2018, 08:21 AM   #8
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Being the contrarian here, I think the 2p6s is a better configuration for the simple reason if one battery cell fails in a non shorting manner, your battery bank capacity is just reduced by that one cell or a little over 8%. The same failure in the other configuration results in a 50% loss of capacity..... while I don't know the internal construction of the firefly battery I assume there are two separate 2 volt cells in each battery case.
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Old 12-20-2018, 02:10 PM   #9
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Being the contrarian here, I think the 2p6s is a better configuration for the simple reason if one battery cell fails in a non shorting manner, your battery bank capacity is just reduced by that one cell or a little over 8%. The same failure in the other configuration results in a 50% loss of capacity..... while I don't know the internal construction of the firefly battery I assume there are two separate 2 volt cells in each battery case.

I'm pretty sure you still lose half the capacity, or more accurately, only half the capacity is usable. The reason is because one of the 2P sets is now 1P, and it will drain twice as fast at the other 2P sets in the series string. When the 1P set becomes drained, which will be at about the half-way point for the rest of the sets, it's voltage will drop and quickly bring the voltage of the whole bank down. Essentially you end up with 0P for one if the sets because one cell is dead and the other is drained.


Now with 2V cells you might be able to keep running at a reduced voltage (2P5S), but if you don't remove the 1P set I think you will kill it dead pretty fast.


But removing the defective cell pair could be an effective work around, turning the bank into 2P5S (10V). It would be pushing it with a 12V system, but in a pinch....


I had cell failures in a 48V system twice, and both times bypassed the defective 2V cell and ran that way (with adjusted charge voltages) for several months while waiting for a replacement cell.


Back to the proposed configs, one advantage to a 6S2P is that if there is a cell failure, you can more easily work around it by disconnecting the string with the junk cell, and running on the other half. I'd even recommend installing a battery on/off switch for each string so they can be disconnected with the turn of a switch. It makes it really easy to test to be sure each string is working correctly with out influence from the other string - something that is otherwise pretty hard to do. And if there is a problem, just turn off the bad string and continue on at half capacity.
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Old 12-20-2018, 03:03 PM   #10
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I'm pretty sure you still lose half the capacity, or more accurately, only half the capacity is usable. The reason is because one of the 2P sets is now 1P, and it will drain twice as fast at the other 2P sets in the series string. When the 1P set becomes drained, which will be at about the half-way point for the rest of the sets, it's voltage will drop and quickly bring the voltage of the whole bank down. Essentially you end up with 0P for one if the sets because one cell is dead and the other is drained.

I think if you look at the firefly battery there are 2 independent 2 volt cells in each case. I referred to an individual cell failure not the entire battery. Batteries can fail in all kinds of ways but electrically they will these failures will either create a higher resistance or lower. if it is low enough likely there will smoke or lots of heat... If the resistance or the ability to accept a charge goes higher or opens entirely instead it effectively reduces the the amp hour rating from 900 to 450 just for that battery. in discharge mode as the voltage begins to drop on the remaining good cell I believe that the rest of the bank will try to replenish the electrons in that cell as well as servicing what ever load there is. This is just the same as having gcs and l16s in a house bank Amp hour capacity in this case is not the weakest link but the average link..
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Old 12-20-2018, 04:59 PM   #11
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I think if you look at the firefly battery there are 2 independent 2 volt cells in each case. I referred to an individual cell failure not the entire battery. Batteries can fail in all kinds of ways but electrically they will these failures will either create a higher resistance or lower. if it is low enough likely there will smoke or lots of heat... If the resistance or the ability to accept a charge goes higher or opens entirely instead it effectively reduces the the amp hour rating from 900 to 450 just for that battery. in discharge mode as the voltage begins to drop on the remaining good cell I believe that the rest of the bank will try to replenish the electrons in that cell as well as servicing what ever load there is. This is just the same as having gcs and l16s in a house bank Amp hour capacity in this case is not the weakest link but the average link..



I've assumed you are treating each 2V cell as a separate cell. Hence 2P6S, not 2P 3S


That "sharing" you describe happens when cells are in parallel with each other. So if a 4P set of cells becomes 3P, the surviving cells will all discharge together, and equally.


But that doesn't happen with series wired cells. With series wired, the current through each cell group is the same, so the Ah drain on each is the same. If you pull 100Ah out of two 100Ah cells, you will be at 50% SOC. But if you pull that same 100Ah out of a single 100Ah cell, it will be totally flat, and there is nothing the other series cells can do to help it. So even though the remaining cells area all at 50% SOC, the voltage of the string will have dropped low enough to shut everything down because that single dead cell is not longer producing any (or much) voltage. And even if you gear can tolerate the low voltage, and further discharge will quickly and permanently ruin the single cell.
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Old 12-21-2018, 09:17 AM   #12
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How to Determine Battery Bank Configuration Label/Name?

TT, OC, et. al. interesting conversation, thank you. I'm going with the 6S2P 'twin banks' concept because it is simpler to cable up, just seems generally easier to understand. I'm gonna go with a switch on each bank, that is a simple and solid backup to shorted/open cell issues.

TT, correct about the transposition error on the old bank. I'm still learning battery bank nomenclature. What makes my old bank either a 3S2P or a 2P3S? I'm not sure how to determine the 'S' vs. 'P' priority when naming a battery bank configuration.
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Old 12-21-2018, 12:00 PM   #13
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A Curious aside question and that is why are you going to Firefly? Have you gotten reports from long term users that encourage you or still a bit on a hope of what they might be? Asking simply because user feedback other than through Bruce Schwab or someone referred to by them has remained somewhat difficult to find.
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Old 12-21-2018, 01:46 PM   #14
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TT, OC, et. al. interesting conversation, thank you. I'm going with the 6S2P 'twin banks' concept because it is simpler to cable up, just seems generally easier to understand. I'm gonna go with a switch on each bank, that is a simple and solid backup to shorted/open cell issues.

TT, correct about the transposition error on the old bank. I'm still learning battery bank nomenclature. What makes my old bank either a 3S2P or a 2P3S? I'm not sure how to determine the 'S' vs. 'P' priority when naming a battery bank configuration.

Maybe the markup below will help. The circled batteries are pairs wired in series. Since each group consists of 2 batteries wired in series, they are each "2S".


Then, there are three of those wired in parallel. That's the "3P" part.



So, starting with individual cells, they are first wired as 2S, then wired as 3P, hence 2S3P.


If you have individual cells wired in parallel, then wired in series, it would be 3P2S.


Hope that helps.
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Old 12-21-2018, 01:49 PM   #15
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"A Curious aside question and that is why are you going to Firefly?"

The FFs are a good interim setup on my way to LFP. I like the FF PSOC properties. I got mine from Coastal Climate Control, they tell me they've had a very good record with them, I like CCC. With the exception of height, the FF L15+ footprint is almost identical to my old T105s, with twice the Ah capacity, no more dealing with acid and watering. Plus I retain the capacity to go to 24v with the same bank, something I'd like to do due to a really MickeyMouse existing bow thruster setup. I realize I'm a relatively new adopter and taking a chance with them, will report on their performance down the road.
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Old 12-21-2018, 05:43 PM   #16
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I think many people will be very interested to see how you like them over the ensuing years.
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Old 12-22-2018, 09:38 AM   #17
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Balanced vs. Unbalanced - 3P2S

Thanks TT, that does help. Over time I will get it as to which part is wired First and which Second. Here's a sketch of what a T105 3P2S configuration would look like imo--it is also a 'Balanced' configuration I believe. You can see where I first put the Series Jumper (whiteout), which would have methinks severely unbalanced the entire bank....
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Maybe the markup below will help. The circled batteries are pairs wired in series. Since each group consists of 2 batteries wired in series, they are each "2S".

Then, there are three of those wired in parallel. That's the "3P" part.

So, starting with individual cells, they are first wired as 2S, then wired as 3P, hence 2S3P.

If you have individual cells wired in parallel, then wired in series, it would be 3P2S.

Hope that helps.
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Old 12-22-2018, 09:44 AM   #18
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I think many people will be very interested to see how you like them over the ensuing years.
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Old 12-22-2018, 12:50 PM   #19
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The part that keeps me confused is that over the years we've had others do the same but no one ever reports back talking about how wonderful and saying they'd do the same thing again. I get the feeling the benefits are there, but more on the line of slight improvement than of revolutionary.
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Old 12-22-2018, 05:46 PM   #20
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Thanks TT, that does help. Over time I will get it as to which part is wired First and which Second. Here's a sketch of what a T105 3P2S configuration would look like imo--it is also a 'Balanced' configuration I believe. You can see where I first put the Series Jumper (whiteout), which would have methinks severely unbalanced the entire bank....
Rgds, Wil

Yup, you got it!
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