diy solar

diy solar

BMS help

Tim Tim said:
If you google and look at images you will find many charts exactly the same but remember LifePO4 are different to AGM and lead acid etc. The discharge curve is very flat then suddenly drops off quickly so the accuracy of using voltage is very questionable. The more accurate way is to measure with a shunt.
Click to expand...

Yeah I can see that. I watched some YouTube videos yesterday (solar garage guy) doing tests with charging and the cells getting full with lower volts going into absorption at different times. The relationship between volts and actual soc seems pretty thin.
 
slowbutsure said:
Yeah I can see that. I watched some YouTube videos yesterday (solar garage guy) doing tests with charging and the cells getting full with lower volts going into absorption at different times. The relationship between volts and actual soc seems pretty thin.
Click to expand...
Exactly!

Did you charge your cells to 3.65v For the top balance. If you did and let them sit for a while you will actually see a small voltage drop. At 3.346 per cell you are close to 99% and if you really are concerned what the BMS states you can adjust it in the Parameter Settings. On mine I have set it to 90% at times and just let the BMS recalculate the SOC after a partial discharge and charge.
 
I have a Victron smart shiny and it has a setting for charged, the voltage that = 100%. I can’t remember if this is meant to be set a bit lower than the absorption voltage or a bit higher. Any idea? Thanks.
 
slowbutsure said:
remember if this is meant to be set a bit lower than the absorption voltage or a bit higher. Any idea? Thanks.
Click to expand...
It a user setting and you can an set it anywhere you want. it does not affect the actual SOC. It just affects when your BMS resets to 100 percent. I prefer to only charge my cells to 3.45 volts which is approximately 90 percent. However I also set the reset number to 3.44 so I know it will reset to 100 percent at he end of each charge. To compensate I also reduce the setting for capacity of my pack so the Coulomb counters will decrease faster and get to zero before my pack is actually zero.
 
slowbutsure said:
I have a Victron smart shiny and it has a setting for charged, the voltage that = 100%. I can’t remember if this is meant to be set a bit lower than the absorption voltage or a bit higher. Any idea? Thanks.
Click to expand...

Ok not sure what you mean. Can you clarify as I think you are talking about your shunt.

What are your bulk, absorption and float settings i thought Victron had a LifePO4 setting so that you didn’t have to change anything. I will look at the manual tomorrow for you to check. In relation to no amps going into your battery, where are you taking the reading? On the solar controller, BMS or a shunt. I have two Daly BMS’s and neither of them will show a current of 1 or 2 amps on the display, yet they will show tenths of an amp when they do show a current. I actually need to do some setting adjustments to get a more accurate reading.

One also has a software glitch that indicates the battery being discharged when in fact it is being charged, and a charging current when being discharged lol.
 
Last edited:
Very little seems straight forward! I hope you get it resolved.

The “charged” setting in my Victron shunt I think is just for it to reset to 100% so thinking about it, that would need to be a bit less than the absorbtion volts or else the shiny will never reset to 100% soc. I think!

I have absorbtion set to 3.45v (27.6v altogether). And I have float set to 3.42.
 
my Victron charger is in bulk mode. I have 8 amps load coming out of the batteries but no charge currently going into the battery. Charger settings:

Absorb. 27.6
Float 27.5

Any idea why the bms is seeing fit not to take any current in? Thanks.
 
my Victron charger is in bulk mode. I have 8 amps load coming out of the batteries but no charge currently going into the battery. Charger settings:

Absorb. 27.6
Float 27.5

Any idea why the bms is seeing fit not to take any current in?
 
Last edited:
Tim Tim said:
Ok not sure what you mean. Can you clarify as I think you are talking about your shunt.

What are your bulk, absorption and float settings i thought Victron had a LifePO4 setting so that you didn’t have to change anything. I will look at the manual tomorrow for you to check. In relation to no amps going into your battery, where are you taking the reading? On the solar controller, BMS or a shunt. I have two Daly BMS’s and neither of them will show a current of 1 or 2 amps on the display, yet they will show tenths of an amp when they do show a current. I actually need to do some setting adjustments to get a more accurate reading.

One also has a software glitch that indicates the battery being discharged when in fact it is being charged, and a charging current when being discharged lol.
Click to expand...
Yes I meant shunt. I don’t like how the bms can mysteriously do or not do things. It’s like trying to learn some secret code. No manuals just hundreds of YouTube videos to filter.
 
slowbutsure said:
Yes I meant shunt. I don’t like how the bms can mysteriously do or not do things. It’s like trying to learn some secret code. No manuals just hundreds of YouTube videos to filter.
Click to expand...
Set your charged setting on the Shunt to 14.6v.
Set absorb to 28.8v
Set Float to 27.6v

Put some serious current draw on your system like a 1000w heater, 3amps at 24v is just a trickle.

You seem to be overthinking the role of the BMS and what it actually does. It does not make the decision of whether to take current in. In simplistic terms all it does is protect the battery in general from being over charged or discharged. It protects each cell in the battery from being over charged or discharged, it does some cell balancing and can monitor the temperature. It does not control the charging and discharging of the battery unless the voltage exceeds the BMS settings Or it detects a fault. There is however a function in Parameter Settings to turn charging and discharging on or off but I would not expect it to have been changed.
 
Tim Tim said:
Set your charged setting on the Shunt to 14.6v.
Set absorb to 28.8v
Set Float to 27.6v

Put some serious current draw on your system like a 1000w heater, 3amps at 24v is just a trickle.

You seem to be overthinking the role of the BMS and what it actually does. It does not make the decision of whether to take current in. In simplistic terms all it does is protect the battery in general from being over charged or discharged. It protects each cell in the battery from being over charged or discharged, it does some cell balancing and can monitor the temperature. It does not control the charging and discharging of the battery unless the voltage exceeds the BMS settings Or it detects a fault. There is however a function in Parameter Settings to turn charging and discharging on or off but I would not expect it to have been changed.
Click to expand...

Yeah over thinking is exactly where I am at the moment while transitioning to lithium.
 
Inverters. I have a 3000w inverter but I’m getting more battery cells so want a bigger inverter. I haven’t had the inverter that long, it was a bit of bad planning on my part. I have seen that inverters get quite expensive when you get over 3000w so I’m wondering about just getting another 3000w inverter. Any thoughts about having two inverters on one system? I’ve seen something about “stacking” to double the watt output of the inverters but don’t really get it. Or have two different power supplies both at 3000w, any thoughts?
 
slowbutsure said:
Inverters. I have a 3000w inverter but I’m getting more battery cells so want a bigger inverter. I haven’t had the inverter that long, it was a bit of bad planning on my part. I have seen that inverters get quite expensive when you get over 3000w so I’m wondering about just getting another 3000w inverter. Any thoughts about having two inverters on one system? I’ve seen something about “stacking” to double the watt output of the inverters but don’t really get it. Or have two different power supplies both at 3000w, any thoughts?
Click to expand...
Firstly you need to think of the end game and what you want to achieve. Look at the appliances you will be using at the same time and total wattage. Yes you can run two inverters and they do not have to be the same size. Remember also they will be using power in standby unless you turn them off and whatever power you use each day you need enough panels to replace it. Plus a little more with the limited UK sunshine ;)
 
Tim Tim said:
Firstly you need to think of the end game and what you want to achieve. Look at the appliances you will be using at the same time and total wattage. Yes you can run two inverters and they do not have to be the same size. Remember also they will be using power in standby unless you turn them off and whatever power you use each day you need enough panels to replace it. Plus a little more with the limited UK sunshine ;)
Click to expand...

Ah yes, British weather. I’m currently sat inside a tent in the rain! The idle amps is a concern, although with the upgrade I will have 16 x 180ah cells to make 24v 1200wh of battery capacity and 2.5kw of panels. My current set up is enough for what I’m running now but I want to add a washing machine.
 
Question. Would it be ok to connect in paralell two sets of cell, same make, but one set being 280ah and one set being 305ah?

Thanks
 
slowbutsure said:
Question. Would it be ok to connect in paralell two sets of cell, same make, but one set being 280ah and one set being 305ah?

Thanks
Click to expand...
Yes
They will balance out with each other, after a few cycles. Just make sure that the voltage is within 0.5 volts of each other, before connecting together. To avoid high inrush current.
 
Hi, I wanted to put my battery under some strain (8x 280ah 24v). I put the washing machine on pulling 2300w according to the shunt. My cells went from 3.34v each to 3.24v very quickly. Is this indicative of anything? I didn’t think lithium dropped that quickly?
 
slowbutsure said:
Hi, I wanted to put my battery under some strain (8x 280ah 24v). I put the washing machine on pulling 2300w according to the shunt. My cells went from 3.34v each to 3.24v very quickly. Is this indicative of anything? I didn’t think lithium dropped that quickly?
Click to expand...
Depends on what "very quickly" means.
That's an 86 amp load on the batteries, plus inefficiencies. At 85% efficiency It's 101 amps.
 
That seems too fast. But, it depends on the quality of the batteries. That's only a .35c discharge. (Assuming it was the only load)
 
Do you know what the SOC was, before adding the load? 3.34 is in the flat part of the curve. It could have been anywhere from 30% to 90%. Depending on if it was discharging, charging, or resting.
 
timselectric said:
Do you know what the SOC was, before adding the load? 3.34 is in the flat part of the curve. It could have been anywhere from 30% to 90%. Depending on if it was discharging, charging, or resting.
Click to expand...

Good question, the bms said 85% and went down to about 75%. Soc seems to be a bit of a mystery with lithium.
 
As long as the battery reaches 100% occasionally. The BMS should be able to track the SOC accurately.
 
slowbutsure said:
Hi, I wanted to put my battery under some strain (8x 280ah 24v). I put the washing machine on pulling 2300w according to the shunt. My cells went from 3.34v each to 3.24v very quickly. Is this indicative of anything? I didn’t think lithium dropped that quickly?
Click to expand...

This explains what you are seeing.
https://aklectures.com/lecture/term...orce-terminal-voltage-and-internal-resistance

Try it again and take a reading of the battery voltage under load. Once you have turned off the appliance, wait a while and watch as the voltage of the battery increases. My lithium packs do after running the aircon and with my AGM battery it will show well below 12V and then climb steadily once I have turned off the power.
 
You must log in or register to reply here.

Similar threads

A
24v vs 48v
Replies
5
Views
346
timselectric
T
G
Which Battery
Replies
0
Views
117
glennjr1
G
B
Need to upgrade help!
2
Replies
42
Views
2K
Barridge
B
F
Selector Switch on MPPT Controller for Different Charge Profile
Replies
6
Views
216
Suijkerbuijk
S
S
Higher amps hurt effectiveness of Built-in BMS of 12V LiFePO4s in Parallel?
Replies
21
Views
972
sun_of_a...
S

diy solar

diy solar
Back
Top