Analog fuel gauge for Emus BMS?

[circuit]

Circuit...

We have now tried with new firmware version (it is available on their website) but with no success There is no way to upload Can group module firmware. I have tried with all firmware versions, use factory restore firmware, reset BMS, swap BMS main unit with another one, use other PC, but...NO GO
I will let you know If/when we will found the solution.

Sorry to hear that. I'm afraid I will not be able to help with this, as I am not familiar with this problem. I will ask around, maybe something comes up.

 

[Eskutr]

Thanks a lot, that's clear now. Wishing you a nice evening.

Thanks. If you face any more issues with Emus BMS installation - let me know.

Hi circuit,

thanks for your advice so far.. we built the SOC circuit as you described and that is great, but there is another problem now that is quite basic - it looks like the Emus BMS does not retain SOC charge info on power off!

We setup with initial SOC = 60%, this was recognised on the control panel correctly. But then after power off and restart of scooter the control panel reading was back to SOC=0% and fuel gauge reading empty

Do you know if the BMS really loses all SOC information on BMS power off, or is there something we must do in the setup? I really hope we made some simple mistake since it's not really practical to leave the BMS on permanently is it?

Thanks for any insight and have a nice day.

 

[Eskutr]

Thanks a lot, that's clear now. Wishing you a nice evening.

Thanks. If you face any more issues with Emus BMS installation - let me know.

Hi circuit,

I just heard back from the company that makes the 'Smiths Flight Gauge' about connecting it to the Emus BMS. They said:

"The standard Flight fuel gauge is set up for a resistive sender, 10 ohms at empty to 180 ohms at full.
So, this could theoretically be driven by pwm... The input has a 220 ohms resistor pulled up to the gauge’s internal 5 volt rail."

In this case, how would you recommend wiring the SOC OUT signal?

(FYI for anyone doing the same - 'Smiths' said it's also possible to make a version of the gauge driven by 0-5V DC, but that has to be ordered specially from them at caigauge.com.)

 

[circuit]

Hi circuit,

I just heard back from the company that makes the 'Smiths Flight Gauge' about connecting it to the Emus BMS. They said:

"The standard Flight fuel gauge is set up for a resistive sender, 10 ohms at empty to 180 ohms at full.
So, this could theoretically be driven by pwm... The input has a 220 ohms resistor pulled up to the gauge’s internal 5 volt rail."

In this case, how would you recommend wiring the SOC OUT signal?

(FYI for anyone doing the same - 'Smiths' said it's also possible to make a version of the gauge driven by 0-5V DC, but that has to be ordered specially from them at caigauge.com.)

Okay, so it looks like their gauge requires an "inverted" sensor. That is not a problem, can be change in software.
I was unable to find a datasheet, so I guess it has the same three terminals: +12V, ground and input. In such case schematic remains absolutely the same. One additional thing you can do is to connect 180Ω resistor in parallel to transistor (between Drain and Source / pins 2 and 3).

 

[Eskutr]

Hi circuit,

I just heard back from the company that makes the 'Smiths Flight Gauge' about connecting it to the Emus BMS. They said:

"The standard Flight fuel gauge is set up for a resistive sender, 10 ohms at empty to 180 ohms at full.
So, this could theoretically be driven by pwm... The input has a 220 ohms resistor pulled up to the gauge’s internal 5 volt rail."

In this case, how would you recommend wiring the SOC OUT signal?

(FYI for anyone doing the same - 'Smiths' said it's also possible to make a version of the gauge driven by 0-5V DC, but that has to be ordered specially from them at caigauge.com.)

Okay, so it looks like their gauge requires an "inverted" sensor. That is not a problem, can be change in software.
I was unable to find a datasheet, so I guess it has the same three terminals: +12V, ground and input. In such case schematic remains absolutely the same. One additional thing you can do is to connect 180Ω resistor in parallel to transistor (between Drain and Source / pins 2 and 3).

Thanks for the quick reply, we appreciate your time.

PS. attached is a photo of the assembled components according to your instruction. Please would you have a look, it's right?

 

[circuit]

Yup, that is correct!
If there will be some linearity error, you can connect 180Ω resistor between gauge input (thick yellow) and ground (blue).
Please note that it is recommended to connect gauge's ground wire directly to BMS and not somewhere else (chassis of the vehicle, etc). Or else the transistor may get damaged during maintenance.

About maintaining the SOC... I think there was such issue with older firmwares. When did you buy the BMS? I'm not sure which one you are running and if latest v1 has this feature. If you are, you might want to try newest v2 firmware (and v2 PC software).
This BMS was intended for larger vehicles, where 12V is always available and only "ignition" input is switched off. There is a battery inside the BMS to retain various active parameters (SOC, ongoing statistics) and to keep the clock running, however it needs a lot of time to recharge if BMS was kept in storage/off for long period of time. With new firmware, if internal battery has depleted, no values are lost and clock does not reset (but stops running, obviously). Note that configuration values are in other memory and are not power-dependent.

 

[Eskutr]

Thanks for all your help.

 

[Eskutr]

Hi,

we are using Emus BMS control panel v2.0.1 connected to BMS version 2.0.4 and it appears that the unit will not preserve SOC information after power on-off. We always see SOC changed to 0% on restart.

Does anyone have experience of this problem?

PS. Whilst we are talking about SOC, we also note that Emus BMS current measurement is lower than actual metered use during testing - eg with accessories on our scooter's consumption is 1.08A, but BMS displays only 0.6A use.... Result is SOC declines slower on BMS than is actual. We have already moved signal wires well away from the power cables and zeroed out the current sensor.... anyone know is it possible to adjust it to more accurate reading please?

Thank you for your time.

 

[circuit]

Just for sake of other readers, this topic has been discussed here:
http://endless-sphere.com/forums/viewtopic.php?f=14&t=56430

Try to update the firmware, that should fix the issue. I'd also recommend to power on the BMS and leave it on for couple of days - this will re-charge internal lithium coin battery and it will improve saved SOC level accuracy (because SOC is not very frequently saved into EEPROM to preserve memory cycling life).

About the current sensor... It is intended for currents up to ±1000A, so 0.6 amp drift is only 0.06%, which is quite good. Even on lower range of ±100A it is still only 0.6%.
What you should do:
1. insert calibration values written on bottom of current sensor's body
2. Do a "reset to zero" (do so when actual current is 0).

If accuracy is not good enough after you do so, consider a third party current sensor. Such as something from BYD, BSY2-150/4IOV2 for example. It depends on what is your maximum current (add ~30% room). Let me know when you get one, I'll help to hook it up, as it is not very straight-forward as original Emus current sensor.
But keep in mind that 0.6% accuracy will be hard to achieve with any kind of sensor.

P.S. In my applications, BMS is active only when there is charging or driving going on (and short periods during traffic, etc), so it is strange that you are idling with BMS on.

 

[circuit]

Did this resolve your issue?

 

[Eskutr]

Did this resolve your issue?

Hi Circuit,
Yes, thank you. Upgrading to the newest software (Jan 2014 release) keeps SOC on.
We tested the amp/SOC and changed the L value to make it more accurate. You're right though, it actually doesn't make that much difference, we're being a bit picky to be honest.
Thanks for the advice about when is best to have BMS on.
Have a nice day.

 

[klikhier]

@circuit it's been a while since you've posted a diagram for a module to put in between the emus BMS and the original analogue fuel gauge (jan 2014). My VW Bug has a thermal type fuel gauge with a rheostat that has between 73 Ohm (empty) and 10 Ohm (full) resistance. Does your diagram also apply for this and/or what are the exact components I need. Happy to hear, many thanks in advance!