Lithium batteries.... Do they float?

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Macua85
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Re: Lithium batteries.... Do they float?

Postby Macua85 » Sun Oct 14, 2018 11:50 am

I hate it when that happens, just wrote a long reply and lost it.

Cell balancing is taken care of by the BMS, info here: http://files.ev-power.eu/inc/_doc/attac ... -Smart.pdf

This one will be brief. My set up, aside from the BMS with the 2 relays and battery, is the same that would be rquired in a system with victron batteries. It works in the same manner using control feeds to turn on/off loads and chargers.

BMV 702 is required for accurate charge/ load / discharge data when there are loads other than the inverter. I am not sure, but think that would also be the case with Victron batteries as they only have cell balancing and temp sense/voltage. The data sheet mentions nothing about SOC calcs, amps in/out monitoring etc.

The contactors don't need to be high current.

I think a battery protect would be needed in any system where loads are not drawn from the inverter, i.e other house loads, see here: https://www.es-store.co.uk/documents/pr ... asheet.pdf

Pretty sure most systems would have this. The additional high voltage layer of protection I have added using the BMV 702 relay is not a necessity, but I can do it, so will.

As for price, apples with apples.
400ah victron: 2 x 12v 200ah batteries £2299 x 2 + BMS £110 = £4708 + shipping

400ah Winston + BMS + Relays: £2252 (2560euros from my invoice including shipping) + say £10 for 2 SPDT relays = £2262

Considerably cheaper!

Re fuses I do need to add one between buck boost, and van loads. The Easysolar has 250a fuse built in which the inverter and MPPT run through.


Hope the above clarifies.

crinklystarfish
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Re: Lithium batteries.... Do they float?

Postby crinklystarfish » Sun Oct 14, 2018 12:00 pm

Posts crossed:

crinklystarfish wrote:Jeez, I'll bet you two can wire fairy lights without too much hassle.

This level of electickery is well beyond me but isn't the inter-cell management courtesy of the cell boards?:

https://files.i4wifi.cz/inc/_doc/attach ... -Smart.pdf

Also - for info of anyone considering LiFePO4 fully integrated solutions at:

http://eza.fr/pile%20eza.html

I don't think they have English pages but the Chrome browser should translate OK.


Previously posted also...

Macua85, just out of curiosity have you crunched any numbers in terms of how much access to your chosen air-con system would give you over a conventional lead-acid based system? I'd imagine that running fridge / pumps / other domestics will mean you'd not want to ever get to a point where the BMS is cutting out supply to prevent over-discharge so just wonder if you've quantified the perceived advantage. I guess it will only be theoretical according to manufacturers' claims but just wonder how many (more) hours / minutes you could hope to run an ac system.

Macua85
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Re: Lithium batteries.... Do they float?

Postby Macua85 » Sun Oct 14, 2018 12:59 pm

Hi,

I've not delved into it in great detail, however the primary driving force (aside from the weight saving which trumps other reasons) was the high loads for any length of time. My old van had lead acids, and when a large load ~80a was put on the battries, the voltage would often dip enough to cut the inverter out after a few mins. I had Trojan T-105 6v 220ah batteries x4, two banks, so 440ah (or 220 accounting for useable capacity). Very possible that my lack of care for the batteries over the years had ruined them (wish I had the foresight to install a low voltage cut off).

I've got the Dometic Freshjet 1700, which according to makers literature used 620w in cooling mode, so 2.7a @ 230v, or 51.6a at 12v. With 400ah lithium, assuming 75% useable capacity, I have 300ah, so in theory should run aircon for nearly 6 hours...in theory! the solar should top up ~25a in decent sunlight, reducing aircon consumption to ~26a = 11h (in direct sun). Its all very rough calcs, but it shows that when we leave the van with dog in, we can do so without worring for a few hours at least. The other main consumer will be the fridge when aircon is on, which I believe is average of 1.6a so negligible.

I don't foresee us running the aircon for any length of time when we are in it and can use the windows/roof fans. I have spec'd the system to be able to run the aircon in the back while driving, which is (just) possible with the buck boost and a tiny bit of solar. I may ultimately parallel in another buck boost.

Its totally theretical, and more than happy to post real world results when it's up and running.

Thanks,

Anthony

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christyler
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Re: Lithium batteries.... Do they float?

Postby christyler » Sun Oct 14, 2018 6:02 pm

Yes, so there is more connections to the BMS than is show on the circuit diagram,. I should have know that !!

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NeilandPat
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Re: Lithium batteries.... Do they float?

Postby NeilandPat » Sun Oct 14, 2018 8:02 pm

Dont know much about lithium and charging. But dont forget that when its'really hot and the ambient tempreture in the vehicle including the batteries are at 40 degrees. Most chargers back of at this point as their default action is to protect the batteries.
So even though you have tons of solar potential you might find that your chargers are only putting in 1 or 2 amps.

I have just gone through 6 weeks of this in Brazil and battery management becomes a real priority.

Ironic really . You wouldnt expect issues in the sun

I dont know if this issue also exists with lithium.

Neil

Macua85
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Re: Lithium batteries.... Do they float?

Postby Macua85 » Sun Oct 14, 2018 8:21 pm

Ah yes, my bad. This is very much a simplified ‘line’ drawing and misses out the intricacies of the component wiring.

As for temps, I believe the lithium’s are suspectible to the same but not sure of the severity. I am installing a thermostatically controlled fan and a (thermostatically controlled) heating element connected to the under floor heating system to maintain the optimum temps under use.

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christyler
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Re: Lithium batteries.... Do they float?

Postby christyler » Sun Oct 14, 2018 9:40 pm

anyway, it looks like a good system, i can't see any problems with it, i should work really well.
i look forward to seeing the finished product.


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