AGM to Li

[Wilbor]

But if you did?

My brake compressor and vacuum pump would come on and if I didn’t hear it it would run until my battery was flat, but I was just responding to “ something you guys don’t have in your motorhome”

[T1 Terry]

Something you guys don't have in your motorhome, breakaway brakes the pin was accidently pulled when the caravan was in the shed and completely flattened my AGM...never been the same since
Hence concentrating on low voltage cut off at 12 V if I can get away with that.

BMS, Any reason why I cannot use this? and maybe wire 3 of them in parallel for 300AH.
https://www.ebay.com.au/itm/3S-4S-100A- ... HuCJ81IUww

The bit that might be an issue is the 10 amps per unit charging current and the 3.75+/- 0.05v so a possible 3.8v before charge cut and that is a little high, but apart from that it looks interesting, looking forward to your report on how well it works. It doesn't appear to come with an enclosure and no mention if it needs forced cooling, but the balance is only 0.42 amps so maybe not a problem? Who knows until one is actually tested, ya gunna be the test pilot?

T1 Terry

[cruiserxxx]

Ordered one of those, I am tempted not to run the charge thru the board nor the load. Discharge 1 cell a little and see what happens.

[cruiserxxx]

Re: China direct 300ah Li import at $1400.00
Got around to some testing with the system 90% complete
And used the Dingo with shunt to measure amp hours.
Charged the batteries as manufacturers instruction, in 12V configuration so maybe they were not fully charged and balanced .
Beginning of the test Batteries were sitting on 13.2v volts
For the fist two hours was upping the amps to 116 to 190 amps this caused the voltage to drop to 12.7
Was having problems with the inverter dropping output voltage from 240v TO 80V, taking this up with the inverter supplier as its rated
3000 to 3500 watt and intermittant up to 7000 watts.
For the rest of test had to nurse the inverter at 30 amps when the thing would only put out 80v to 90 amps when it kicked in at 240v.
The rest of the system performed good no warm spots in any connections or cables.

End test ...the inverter cut out!!! 279AH individual cell readings 2.63, 2.54, 2.64 and 2.71 under load
Spec was 300AH.

At 267AH individual cells 3.0 2.97 2.99 2.98 under load
230AH all cells 3.16 under load
Which is indicating cell balance might become a issue below 80% discharge.

Wired all the cells in parrallell now and charging at 3.4 volts approcx 25 amps...thats going to take a while to them charged again.
Decided not to bottom balance before charging, as they are going to top balance.

[BruceS]

Glad it's your money going to 2.54v!!! Ouch!!
Ever going that low again?
You need an ear splitting siren at 2.9v in my opinion!!

[cruiserxxx]

Glad it's your money going to 2.54v!!! Ouch!!
Ever going that low again?
You need an ear splitting siren at 2.9v in my opinion!!

The cell manufacturer recommends discharge to 2.5v for a capacity test.

That happens very quickly when a load of 90 amps is hanging onto the end as the voltage drops under 12V.

Normal use there wil be alarm and a 100 relay that breaks the load circuit thinking about setting that at 3v.
Will never go to 2.5 volts again.
Found another bit of fauty gear, I set the cut off voltage to 12V and it cuts off at 13V.

[T1 Terry]

You need to read all the manufacturers test conditions before you start the test. What was the CA number for the load test? Winston use 0.5CA, Sinopoly use 0.2CA, some of the ohers seem to have a random figure using reverse mathematics, as in, the load is determined by producing the advertised Ah at the end of the test
The Winston test data of 0.5CA would require a constant load of 150 amps for a 300Ah battery and the 2.5v is while the 250 amp load is applied. That 2.5v does not apply for a 100 amp load or what ever, only a 150 amp load. For this reason we have adopted the min cell voltage of 2.8v under load stop discharge no matter what load is applied. As soon as the load is turned off the cell voltage will bounce back to above 3v.
We generally do a capacity test using a Victron BMV with the charge efficiency set at 100% and Peukert Factor set at 1. Set the battery capacity to the advertised capacity and battery isolation cut at 0% SOC or 2.8v. We then start a logging event on the Junsi, charge that battery till the input current drops to less than 1% and all the cell voltages are 3,6v. Disconnect the charger for a few hrs and read the cell voltages, if they have dropped below 3.5v the charging needs to be resumed because the cells are not fully charged. Once all the cells hold 3.5v or better the capacity test can begin, the Junsi will record all the cell voltages through the whole test so we can see any abnormalities in cell behaviour. If you can't get the 300Ah out of the battery without a cell dropping below 2.8v under load, you don't have 300Ah of capacity.
When we service a battery pack after 3 to 4yrs we clean the terminals, clear any memory charge and repeat this same process. So far we have not had a Winston battery pack that we have installed not pass the full advertised capacity test, well accept for the ones that have had an opsy moment as Frank Spencer would say

T1 Terry

[cruiserxxx]

Has anyone isolated the issues with the 100amp SSR,
Is it
1/ Does not like the continuous load
2/ Does not like heaps of switching on and off
3/ Does not like being on 24/7 regardless of load.

How would two / three in parallel stand up 12V continuous 2 - 25 amps with up to 10 bursts per day 5 minutes at 150 amps.

[Busman]

Dunno if I am wrong here but Cruiser, you do seem to be reinventing the wheel ?

[cruiserxxx]

Dunno if I am wrong here but Cruiser, you do seem to be reinventing the wheel ?

Happily Building my Battery Management system now,
Decided not to go with SSR and use a coventional
500amp continuous 900 amp peak soliniod that is rated continious and draws 0.5 amps no load, under $100.00
This will cut the supply to everything straight after the main switch in the event of voltage going out of my preset range.
https://www.amazon.com/Stinger-SGP35-50 ... Z8BDT0KT0B

Then found a high / low voltage switch which I will set for now 11.8V low cut off and 14.8 volts high cut off....$10.00
https://www.ebay.com.au/itm/Battery-Cha ... 2749.l2649
Will also set the solar controller to alarm at 12V

To monitor SOC, cell voltage, total voltage in addition to the solar controller, this cell voltage reader will tell me Total Voltage, each cell voltage, and state of charge, reviews are suggesting its one of most accurate out there....$40.00, this will be switched so is not running all the time.
(Could have got a $16.00 copy but the reviews I have found the copies are not as accurate measuring voltage to two decimal places)
https://www.davestoysforbigboys.com.au/ ... OS+Sentry3

To balance the cells my thinking is to lenghten the cell studs, turn main switch off and in 5 minutes I can have the 12off 100AH cells in parralell and let them self balance while we go for a walk ...see how this goes and if balancing becomes a issue. (Or get those individual cell shunt balancers around my head)

Also dropped the idea of a SSR combined with the 40 amp dingo to increase capacity, found my old powertech MPPT 30 amp solar controller so will run approx 600 watts solar thru the Dingo 40 amps and 200 watts thru the Powertech 30amp MPPT, that should be fun comparing MPPT with PWM in real life!
If I exclude the 3000 / 7000 watt inverter, looks like it is possible to for someone with electrical qualifications to build their own 12v 300ah Li system for under $2000.00 installed with BMS.