Lithium batteries

terriwa · Senior Member

Lithium batteries

terriwa · Senior Member

Meant T1 Terry

T1 Terry · Guru

Sentry lithium batteries, a rose by any other name was I line I think :lol: Check the specs here www.rpc.com.au/pdf/sentry_lithium_brochure.pdf Max discharge rate is 50 amps continuous for the 100Ah advertised capacity battery and weighs 13.8kg. To build a genuine 100Ah 12v battery with the capacity measured at a 50 amps per 100Ah advertised capacity (0.5CA or C2 rate) from just the cells and links to join the cells weighs 16.2kg, then add the weight of a BMS and the plastic case to make it look like an AGM battery and it is going to weigh a lot more than 13.8kg. A genuine 100Ah lithium battery can be continuously discharged at 100 amps and still get the 100Ah capacity out of it, 300amps and you get about 85% of the capacity before the voltage drops below 12v, 500 amps and you get roughly 75% before the voltage drops below 12v while under load. reduce the load to 100 amps or 50 amps from the 100Ah battery after those huge loads and you can still get the full 100% of the rated capacity before the voltage drops below 12v.
So, why only the max continuous 50 amps limit? Is it the poor quality BMS inside or the battery isn't really 100Ah capacity using the accepted lithium battery capacity test method, or maybe the battery is built out of those cylindrical cells that look like AA batteries on steroids, 18650 is the size classification, 18mm diameter and 65mm long. These cells have heat issues if you try to drag too much current through them so that might be another reason the reason for the current limit.
This current limit is the limit no matter how many batteries you put in parallel, e.g. 4 x 100Ah @ 12v batteries in parallel equals 400Ah, but still only a 50 amp max continuous discharge rate.
Why can't you just add the 50 amps from each to make a max of 200 amp discharge limit? None of the batteries have any form of current limiting so there is no way to evenly share the load across all 4 batteries.
We did a demo at this yrs Stone The Crows with 4 x 100Ah Winston celled batteries connected in parallel, a Victron BMV 700 between each and an inverter running a 2400w load, a hairdryer and a cube heater I think it was. The first battery in the chain supplied the majority of the load, the second supplied a bit and next to nothing from the third and fourth battery in the parallel string. After 5 mins the first battery was down to 85% SOC and falling, the second was 95% SOC and seemed to be holding it but was obviously dropping slowly, the third and fourth battery remained at 98% SOC.

we plan to do a You Tube video of the same test but with a bit better display of just what is happening to try and make it easier to understand. Just gotta find the time and someone who can do the video bit without it sounding boring and send everyone to sleep like so many other You Tube video's out there.

T1 Terry

AB67 · Newbie

https://evparts.com.au/12v-lifepo4-batteries/evh12v100ah.html Ev power are quality mob, know there lithium, speak to them

T1 Terry · Guru

A few things concern me about that listing, 2000 cycles for deep cycle use, I would expect a lithium battery with a good BMS to last a lot longer than that, we already have units on the road full time now in their 9th yr, that adds up to over 3,000 days and still going strong. If they are in full time use as these systems are, then that is 3,000 plus nights as well so could that be seen as a cycle?
The phone display when selected shows the right hand dial as voltage and a dial from 100 to 0, the voltage reading is 13.38 yet the needle is at around 11 or 12 what evers because that isn't marked as SOC% only voltage at the bottom. If 13.38v is marked that low on the scale, what voltage is 100?
Look at the battery label in the background of that phone screen shot, the label doesn't agree with the specs on the site do they.
Now look at this unit that is designed to look after multiple 12v batteries it appears, https://evparts.com.au/bcu-nev-04c.html there are 3 x 12v batteries in parallel yet the voltage on the display is 53.4v and the inverter is marked as a 24v unit ..... what the ????

At least it shows they were using the blue cells for those batteries, they are the early CALB cells and their capacity is measured at the C5 rate or 0.2CA or discharged from full battery voltage to the cut off voltage of 2.5v over a 5 hr period. From previous tests with other manufacturers cells marked as 100Ah @ 0.2CA test rate are actually only 75Ah @ the 0.5CA or C2 rate accepted as the standard for testing lithium battery capacity.

That calculates out at $825 (purchase price) divided by 75Ah = $11 per Ah, $11 x 100 = $1100 for a genuine 100Ah battery that still only claims to have a 2000cycle life.

At least the max current and continuous current is more like a genuine LiFeP04 battery

T1 Terry

Noelpolar · Veteran Member

They are GBS cells.... https://www.gbslithiumbattery.com/aboutus.html

I think they at rated at 1/3C.

Anyway..... they aren't $825.... thats the 100ah drop in.... which isn't GBS cells... they do different products.... drop ins..... and the discrete cell batteries.... with either Calb or GBS cells.

-- Edited by Noelpolar on Friday 6th of September 2019 09:46:55 PM

terriwa · Senior Member

thanks T1 Terry for your reply. What brand of lithium battery do you rec.

Thks Greg

T1 Terry · Guru

Noelpolar wrote:
They are GBS cells.... https://www.gbslithiumbattery.com/aboutus.html
I think they at rated at 1/3C.

Anyway..... they aren't $825.... thats the 100ah drop in.... which isn't GBS cells... they do different products.... drop ins..... and the discrete cell batteries.... with either Calb or GBS cells.

-- Edited by Noelpolar on Friday 6th of September 2019 09:46:55 PM

Yes, an unknown when it's inside a plastic case. The GBS cells have a rather dubious reputation, I have 76 x 40Ah cells as a plug in battery pack in my 2006 Prius and the smell of venting electrolyte near takes the breath away in the summer after an overnight recharge at a mere 5 amps. I believe they are roughly 12mths old and have already lost 30% of their capacity. I believe a couple who call themselves Technomads in the US fitted a house pack of these cells and reported the same thing, a loss of 30% in the first yr.

The Calb SE cells are blue, just like the GBS, but the terminal arrangement is different. The GBS cells have a square 4 screw terminal where the Calb SE has the traditional round 8mm bolt type terminal.

T1 Terry

T1 Terry · Guru

terriwa wrote:
thanks T1 Terry for your reply. What brand of lithium battery do you rec.
Thks Greg

There isn't a drop in all in a sealed plastic case battery I'd recommend, not even the Winston 90Ah drop in battery. There is a load of B/S on a few of the sellers sites that say the cells in these batteries are specially match to work together. This is simply not true, they have 4 cells with consecutive part numbers and that just means they came from the same batch run. They are also only LFP chemistry and not the far superior LYP chemistry that is Winston's prime quality cells that were developed by Winston Chung himself. These cells are continually improving with their capacity and cycle life, the latest cells are 3.3v nom. rather than the 3.2v all other LiFeP04 cells are due to their on going development.

If you want a quote on a custom built battery and BMS system for your particular requirements, drop me a PM and I will forward it to my wife so she can give you a quote. You may be pleasantly surprised at the price, quality doesn't have to cost a lot more, but it is more expensive initially than a cheap drop in. If the longevity and continuous back up support is more important to you than the cheap initial cost, then it might be worth the effort, it cost nothing to fine out.

T1 Terry