Over-discharge, ie below 2.5V per cell has the same effect. Drastically reduces the life of the battery. Go below 1.8V and it’s essentially over after a single cycle.
But as you said earlier, these batteries always have a BMS that will at least protect the cells. The reason why I am concerned about a higher charge voltage (14.5V) is because unless the cells are perfectly balanced, one of them will step out, and it will force the BMS to intervene. Ideally you want to avoid that, it causes “stability issues”
More than once I’ve had issues with imbalanced batteries where it took two weeks of cycling to get a low cell up so that I could get the battery up to the requested charge voltage. Had a BYD Premium LV for example that asked for a charge voltage of 56.5V but could hardly reach 54.5V without the BMS intervening. Brand new, with a cell imbalance It all clears up in time, and is not a reason for concern, but it makes things a little less “drop-in” then we would like.
I have one of the BN 8AH batteries. Works fine but have not yet done a capacity test.
See link below for an alternative (Securi-Prod) to the BN 8AH. They are going at a really good price - but are claimed to have capacity of 7AH. I bought a couple and will be doing a capacity test (approx C/10) to see how actual capacity compares to the spec sheet. Why approx C/10 ? Well I need to put a resistor in series to get the approx 700mA but as the battery discharges the voltage drops and then so does the current !
For interest, the BN weighs 1117g and the Securi-Prod 931g.
Indeed! I reckon you need a quick fix to get you out of the starting blocks…
I read about this bench power supply: https://amzn.to/3GepraP
Ok, it isn’t an AC supplied device but has some nice features.
PS: I’ve been looking for a bench power supply for so long now I’ve given up
If you could have gotten to the individual cells, I’ve tried a few ideas.
The latest one, charge the bank using the inverter to like 3.45 - 3.55v per cell (14.2v) if the cells behave, lower volts if not.
Once charged, I switch the inverter off and use EV-Peak to charge each cell individually to 3.65v, switch on the inverter, no load, and let it settle on the float volts overnight, then start using it. Done using Victron settings.
I got this one locally at a pretty reasonable price.
Downside is that it is only a 3 digit display. 4 digit would be better. So I have to use a multimeter to get a more precise voltage if needed.
Making some assumptions but looking at the bottom of the board I suspect about 50mA balancing.
Also, considering this particular battery has not been charged/discharged numerous times I get the following for the cells:
3.332V
3.330V
3.329V
3.332V
Looking at weight etc. to compare these types of batteries will likely not mean too much. This battery at least is filled about 1/3 with a rubberlike substance that keeps the cells from moving around.
Ok I tested my 3x Securi-Prod (claimed) 7AH batteries using a discharge tester that measures the AH discharge and turns off at a selected battery voltage.
I discharged the battery to 11.2V (2.8 V per cell) at approx C/10 using a 20 ohm resistor.
Batteries were all charged to 14.0V
Observations. This is disappointing less than the claimed 7AH. However the discharge rate for the 7AH capacity is not stated on the datasheet so I will test one cell at approx C/25 and see what the results are. BTW the Blue Nova does state on their battery that the 8AH rating is at C/10.
I did a similar test on a 7AH Forbatt SLA some time back at C/10 and also did not get the claimed AH rating
I suspect manufacturers might specify low C-rates when testing a battery to decrease the chances of the bms spoiling the party when volatge drops a bit under heavier load.
Looking at warranty info, regardless of C-rating of the battery, when they specify a standardised test, most specify slow charge (0.2C), rest, followed by a constant 0.2C discharge.
Tested the battery which had a rating of 6394 mAH @ C/10 but now with discharge rate of approx C/20 (40 ohm resistor). Now measured 6445 mAH which is rather surprising as I expected the result to be closer to the 7 AH mark !
For me Secucri-Prod is a suspect brand: One can’t find any site which is theirs. Regal Security comes up as the closest site which makes me think this is a name developed by them.
If so then being a security company they aren’t really in the battery business (a difficult business!)
I had a stand up fight with a large SLA battery supplier wanting them to verify the capacity of their 7Ah batteries. The tech whose responsibility this was went off the deep end yelling and carrying on and by so doing effectively refused to engage me on the subject. They also state boldly that batteries aren’t returnable. Now this response is from a specialised battery supplier. I’ll leave you to draw your own conclusions…
Speaking for SecuiProd PSU’s I have just gone through 3 x new 24v units in the last 2 months, each one a replacement for the previous. Either they trip internally every few minutes or they have a ton of DC noise. This was was a replacement for the original SecuriProd that lasted 10 years. I can only imagine they have downgraded the quality of the components over time.
For comparison I thought it would be good to do a capacity check on the BN (claimed) 8AH battery. I used a 20 Ohm resistor to discharge so the discharge rate was a bit lower than C/10.
I also started with a fully charged battery and discharge cut-off at 11.2V.
The BlueNova measured at a respectable 8001 mAH !
So, as usual, you pay for what you get. The higher BN price gives you a higher quality battery.
I am contemplating a tear-down on one of the SecuriProd batteries to see if there perhaps is a capacity rating printed on the cells .
They are probably using 2nd life batteries and this will be difficult to verify. You need to find someone at an outlet that looks you in the eye and confirms what the deal is. All the promises made on internet sites is 'n klomp kak!
I am almost 100% sure that they are using 2nd life cells, it is almost impossible to build a 7ah battery for the price of R450 using new cells and make any profit on the sale.
I ordered one from my supplier, as soon as stock arrives I am going to tear it down and have a look at the cells and bms its the only way to see what quality product you are dealing with.
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