DIY Lithium

Harryw

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The bus bars have slotted holes, I will measure the max space between the cells. I am using 2mm between the cells and 5mm on the ends.
Yep ditto, I’m doing the 2mm inter layer same dimension as the cells but the 5mm a little wider as I’m going to use hose clamps to give light compression and didn’t want it to touch the sides of the cells.
Pretty reasonable costs and cut to size by these guys.
 

Nabsim

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Not watched those vids but why would you use aluminium for bus bars when copper is plentiful at present?
 

Derekoak

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He had thicker Aluminium that he was surprised were less resistant than the copper. But doubling the copper to the same thickness would have brought the advantage back to the copper.
The other video , the third episode when Dan was testing the heating pads in actual cold conditions . It took 20 minutes to heat 3 degrees. That is with 69 watts of heat under the bottom of the cells. I thought again why does he not put his heating pads between cells 1 and 2 and between 3 and 4. He could cut spaces in some of his cutting board separators to make room. Then instead of the heat needing to conduct 200mm to the furthest points in the cells and 100mm to his sensors he could have only 70 mm to the furthest point in the cells and he could have his sensors at the furthest point. Then he would know the whole cell was warm enough and maybe lower the target temperature?
I can see that as his pads were not to size, things would be a bit uneven, but Phil has found a source of pads made to measure.
 

xsilvergs

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He had thicker Aluminium that he was surprised were less resistant than the copper. But doubling the copper to the same thickness would have brought the advantage back to the copper.

His new aluminium bars had a larger contact area if I remember correctly, doubling the thickness of the copper wouldn't have helped his contact problem in my opinion.

Look forward to your video, the more information that is out there the better chance the rest of us have of getting it right first time.
 

Nabsim

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Copper is a superior conductor. We ended up with a lot of problems after the copper shortage in the 70’s where we had to use aluminium instead. Was on a lot more volts and current than this application though
 

Trotter

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Copper is a superior conductor. We ended up with a lot of problems after the copper shortage in the 70’s where we had to use aluminium instead. Was on a lot more volts and current than this application though
440+. .?
 

SquirrellCook

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What you'll find is that volts are smaller than currents, so if the material is more resistive it's easier to get volts through rather than currents. Don't even think about using sultanas. ;)
 

xsilvergs

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Just ordered a pair of Ecotree batteries, I nearly bought the Poweroad until I found out the cell type at the last moment.
 

xsilvergs

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What cell type is it that you don't want to buy?
Phil, I'm not a fan of pouch cells, had a few fail in devices at home and when I worked. I know some EV manufactures use them and they suffer failures too, Volvo cars being one.

Ecotree use cylindrical cells like Relion and Tesla. Good for cooling and integral strength.
 

xsilvergs

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I don't have a B2B as LiFePO4 does not require absorption or float, it only needs a voltage of bulk of 14v - 14.6v. Victron makes a split charge "Cyrix" relay made for charging LiFePO4 batteries from the starter battery (not directly from the alternator).
@Philip Tomlinson Are you saying that a Victron MPPT charger should be set to ~14.5V with a LiFePo4 battery for both Absorption and Float or do you lower the float?
 

xsilvergs

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You lower the float.
@Philip Tomlinson
So what is your reason for having a Float voltage with an MPPT charger but not having or being bothered when charging from the alternator?
Then in real life I sit in a field, the solar charges the LiFePo4 battery and by lunch time the MPPT goes to float. I now move on so the alternator applies ~14.5 volts to the battery, the same voltage the MPPT was doing a moment ago before it went to float!

I'm probably missing something obvious here so sorry for questions.

Tony
 

Philip Tomlinson

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@Philip Tomlinson
So what is your reason for having a Float voltage with an MPPT charger but not having or being bothered when charging from the alternator?
Then in real life I sit in a field, the solar charges the LiFePo4 battery and by lunch time the MPPT goes to float. I now move on so the alternator applies ~14.5 volts to the battery, the same voltage the MPPT was doing a moment ago before it went to float!

I'm probably missing something obvious here so sorry for questions.

Tony
Because you cannot turn off the float on most MPPT chargers. Setting it at 13.6v will power the BMS units without discharging the battery. LiFePO4 only requires constant voltage charging until the cells reach the set voltage. Once they do reach that voltage no power will flow into the cells so any other charging is irrelevant.

Continuous charging of LiFePO4 batteries is not advised as it can cause the cell voltages to be permanently increased. This does matter when charging from the starter battery as a motorhome is unlikely to have the engine running for long enough to be an issue.
 

Harryw

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On a similar note, my hab PDU is a standard BCA affair and the 12v PS is a 20A 13.8v CV type, it’s actually about 13.7v at the habitation battery terminals.
My thought is there’s nothing wrong with keeping that for the Lifepo as it’s well down the knuckle of fully charging voltage.

Am I wrong to think that? ideally about 13.4v would be better but...
 

Philip Tomlinson

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On a similar note, my hab PDU is a standard BCA affair and the 12v PS is a 20A 13.8v CV type, it’s actually about 13.7v at the habitation battery terminals.
My thought is there’s nothing wrong with keeping that for the Lifepo as it’s well down the knuckle of fully charging voltage.

Am I wrong to think that? ideally about 13.4v would be better but...
14.6v (3.65v per cell) is the MAX that the battery should be charged to. In my opinion 14v-14.2v is optimum to give the batteries a slightly easier life.

The generally accepted float voltage is between 13.4v and 13.8v with 13.6v or below being optimal.

One thing to remember is that these batteries are likely to have 80% capacity after 3000 full cycles (full cycle everyday for 8.2 years) with just a little bit of extra care. Or 80% capacity at 2000 cycles is you abuse them (full cycle everyday for 5.4 years). Of course, if you don’t fully cycle them every day then the time could be a lot longer.

The chances are in ten years a newer battery technology will be available and we will be looking at these batteries like old tubed TVs.
 
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Derekoak

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I was actually searching for information as to whether heating a cold lifepo4 would happen by conduction and convection or just conduction. According to this article there is no free flowing electrolyte in liFePo4 cells it is all absorbed so only conduction will occur in heating cells. The effect of that is that putting heat pads under a lithium cell is not the advantage that it would be in a flooded lead battery.
There is a lot about safety in this article. It also says
" Trickle charging causes all of the lithium present in the cells to be transferred to the positive electrode, whether it can be normally inserted into the carbon cathode or not. Any lithium that cannot be absorbed normally ends up plating the cathode.
From the above, it should be obvious that an operating regime combining fast charges followed by a trickle charging is particularly harmful. A fast charge tends to saturate the anode surface with lithium ions and then any additional charging results in lithium plating. This scenario can quite easily be met on marine installations where a focus was placed on fast recharging through the use of an engine and alternators (or high-capacity DC chargers) and renewable energy systems then fail to properly implement a charge termination and hold the cell voltages up."
I imagine a low float voltage helps stop the concern where the camper is not used and solar charges the battery to full. The sun shines and energy is always available to trickle charge the lithium but float of 13.6v is too low to cause lithium plating?
 
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