New Daly "Smart" BMS w/ Communication. (80-250A)

[BiduleOhm]

Yep, exactly

It's actually 0.0235 %, 2 k would be 0.2 %; also that's assuming the input impedance is 1 M which can be totally off depending on the BMS we talk about. The nice thing is that it's a linear error so if you calibrate for it then it should stay calibrated for all the current values.

If you want to eliminate almost all error then you can use an active filter, but you really need to know what you're doing when you chose the op-amp as we're working with very low level signals, things like Vos can ruin the accuracy if they're too high.

 

[FilterGuy]

It's actually 0.0235 %

Yup.... When I turned my calculator back on the number was still there: .000235. I must have counted the zeros wrong.

I just put an ohm meter across the Chargery sensor input and measured 3.2M ohm while the Chargery was off. I have no idea what the input circuit looks like so I don't know if a static measure like that is valid.

 

[BiduleOhm]

It's not really valid.

If you want to measure really low currents (to then calculate the input impedance) with a standard DMM there's a very nice trick but you must know the input impedance of your DMM (usually 10 M) and have a known voltage (or a second DMM to measure it) to power your load (here something like 50 mV would be nice). Use the DMM in the voltmeter configuration but connect it in series with what you want to measure, like if it was an ammeter. The impedance of your load is equal to: Rdmm * ((Vsupply / Vdmm) - 1)

For example if Rdmm = 10 M, Vsupply = 50 mV and the DMM displays 42 mV then the load has an impedance of 10 * ((0.050 / 0.042) - 1) = 1.9 M

Edit: just thinking if they put an ADC directly without an amplifier this method isn't valid either as the load isn't constant. The simplest thing in this case is to look up the ADC datasheet.

 

[Cal]

Is this the circuit you are thinking?

View attachment 17435

I wonder what the 235 ohm resistance will do to the accuracy? If the input imedence of the meter/bms is 1Mohm it is only .2% of the input impedence so it should not be to bad. Either way, I would want to calibrate the BMS with the filter installed.

Think an electrolytic cap (polarized) would work? Probably not. Leakage current might be too high. Got suggestions for parts?

Simple RC might be better.

 

[BiduleOhm]

You would need 2 back to back, but yeah, main problem is leakage. That's why I linked a ceramic one: https://www.mouser.fr/ProductDetail...EpiMZZMsh%2B1woXyUXj%2BamvhD7guHr8XarkzKCfqU=

 

[FilterGuy]

Think an electrolytic cap (polarized) would work? Probably not. Leakage current might be too high. Got suggestions for parts?

The inverter uses electrolytic caps on the DC input. Adding more big electrolytic caps in front of the inverter would probably help... but you would probably have to add a lot to make a big difference.

If you are adding a filter to the signal line between the shunt and BMS or Meter, you don't need a large capacitor so I would use a ceramic won't age like an electrolytic.

Simple RC might be better.

Take a look at the previous posts.... We considered and rejected an RC filter due to what it would do to the response time of a BMS.

Got suggestions for parts?

I have not looked for them but @BiduleOhm said he found the capacitor and inductor for the proposed LC on Mouser.com.

BTW: Thinking about this, where I saw this problem the worse was on a set-up with way undersized main wires.. I suspect that aggravated the issue. (That system is torn apart and parts used elsewhere. Otherwise I would check my theory) As with so many other things with low voltage and high current...the first thing to do is make sure all your wires and connections are low resistance.

 

[FilterGuy]

That's why I linked a ceramic one:

Funny... I did not even notice the links in your other post. Thanks for doing that.

 

[BiduleOhm]

We considered and rejected an RC filter due to what it would do to the response time of a BMS.

NB: a LC one has the same problem.

 

[Pierre]

Very interesting discussion indeed. Just reminds me of how much theory I forgot since my studies . Have a lot of catch-up to do.

 

[Frank in Thailand]

Almost a thread for the "danger zone" guys!!

My basic knowledge of electronics makes it hard to follow the Wizards.

Daly normally have really good aftersales service.
(But crappy manual writers)

If I understood correctly the main problem is that the BMS provide wrong information about charge, discharge and SOC (who are all somewhat related)

Or am I missing something?

If this is still the main issue, they should be able to fix!

 

[Mikhail]

The SOC problem has already solved. After changing rated capacity you have to reset the BMS in the engineering menu in the program.
About unstable current measurement when an inverter is working - I think there is only one good way to solve it. It is program averaging inside the BMS. It needs firmware update.

 

[Cal]

You would need 2 back to back, but yeah, main problem is leakage. That's why I linked a ceramic one: https://www.mouser.fr/ProductDetail/Taiyo-Yuden/AMK316ABJ107ML-T?qs=sGAEpiMZZMsh%2B1woXyUXj%2BamvhD7guHr8XarkzKCfqU=

Very nice cap: 100 uF, 4V, ceramic
Size: 3.2 x 1.6 mm
Is the body large enough to attach wires to the ends? Or do you need to solder the cap to a circuit board? Guess I’ll find out as the parts will be ordered.

I’m not concerned with the slower response time (if multi stages are required).

 

[BiduleOhm]

Yea, MLCCs have gone a long way, you can have pretty big capacities if you don't need a somewhat high voltage cap. I checked and the less expensive TH one is around 10 $ so that's why I linked a SMD one.

It's a 1206 part so not too small, you can solder wires to it without too much trouble if you want. I recommend tweezers and tinning the wires beforehand.

The simplest without a PCB would be to solder it to the inductor, solder some wires to them and put heatshrink tubing over the thing

 

[Cal]

Almost a thread for the "danger zone" guys!!

My basic knowledge of electronics makes it hard to follow the Wizards.

Daly normally have really good aftersales service.
(But crappy manual writers)

If I understood correctly the main problem is that the BMS provide wrong information about charge, discharge and SOC (who are all somewhat related)

Or am I missing something?

If this is still the main issue, they should be able to fix!

It’s likely the Daly is getting the correct current measurement. However due to the sinusodal ripple current when using an inverter, there’s a chance measurements are skewed towards the peak or trough of the ripple. A software mod will not fix an alias problem. In addition, the displayed current on your monitor will constantly change, depending on the point in time the measurement is made in relation to the ripple voltage. A filter at the shunt is a good fix.

 

[Burnzy56]

I'm hoping I don't regret this but it's done

 

[Airtime]

It’s likely the Daly is getting the correct current measurement. However due to the sinusodal ripple current when using an inverter, there’s a chance measurements are skewed towards the peak or trough of the ripple. A software mod will not fix an alias problem. In addition, the displayed current on your monitor will constantly change, depending on the point in time the measurement is made in relation to the ripple voltage. A filter at the shunt is a good fix.

Hey @Cal did you try out your filter yet? In the Chargery thread I had said I was going to try a simple RC filter, 10k and 2.2uF, 7Hz. I never did try it as I am now using the Electrodacus SBMS0 which does not exhibit this aliasing artifact. I looked at the schematic and guess what? It has a current sense amplifier followed by simple RC filter with 1k and 22uF, then ADC. Same 7Hz corner but different values. It seems to work well, no current measurement problems when I run my inverter.

As to the measurements skewing to peak or trough... at least for the Chargery what I saw was an aliased artifact with a large approximately sinusoidal variation and a period of about 7 seconds. I think any current measurements it takes will have the same distribution as the 120Hz ripple itself, just mixed down to near DC. Although depending on how close the ADC sample frequency is to a multiple of 120Hz, it could mix all the way down to DC or at least a very low frequency with even longer period than 7 seconds.

 

[Cal]

Thanks, interesting info. Looks like the Electrodacus got it right.

But no, haven’t tried the filter. I’m in the Gorge since mid June. Don’t expect to get home till mid August. Some time in September I’ll try it.

 

[Frank in Thailand]

FYI for sale,
one 150A Smart Daly,S16, LiFePO4

Location: Thailand
"World wide shipment,+/- $40,-

i'm going to use the DIYBMS.
serious offers can be made via PM.

 

[salvey]

Hi, new here - thought I'd share my experience with this smart box.
I ordered and received daly 60amp smart bms +bluetooth +uart usb cable. All arrived fine.
In the box: wiring diagram, BMS, spaghetti cable, temp sensor, bluetooth, uart cable and some "on-off" switch.

Had to figure out how to initialise it, apparently, the right sequence is connect everything, then switch to On, then short P- and B-. If the temp sensor is not connected - it won't come up, which is not handy really - I don't need it as we don't have subzero temps here.

I've received a 4S x 150A LiFePo4 Smart BMS and a 16S x 250A LiFePo4 with Bluetooth and UART cables. I am trying to get them working with IPhone AP and UART/PC SW.

- 4S BMS works with the Bluetooth dongle (4-pin JST) and IPhone Ap that appears to be a different one than you are referencing; maybe they have updated this? The Ap only reports data and the parameter setting functions do not seem to work.
- 4S BMS does not work with UART connection to PC. Similar to you, serial connection is confirmed but no data transferred either way. I am using PC SW from download link (not 'new' SW you referred to).

- 16S BMS has 6-pin JST for UART/BT/GPS and I received 4-pin JST cable on Bluetooth dongle so cannot connect. Nothing to report yet.

Have you sorted out your system yet? Are there new SW and APs available somewhere? Thanks.

 

[Frank in Thailand]

For the BT, I might be to help.

They probably shipped a wrong BT connection.

I checked my 6 pin, 4 wire Bluetooth.
It's straight forward, the middle 2 are not used. Nothing twisted or strange.

If you split the 4 cable in 2 pairs, the 2 on the left go left, the 2 on the right go right
You probably can cut the JST into half.



Naturally, not the best solution, it will make it work fast.
Alternatively you can return the BT to the seller and receive one with right JST.