Understood
Checking Chargery voltage measurements
- Thread starter Cal
- Start date
Understood
I have no idea, that is what I tried to express in post #19.
Can anyone explain why Jim cannot power directly from his 24v nominal battery?
1. Chargery informed me Com3 ground (RS232) is connected to BMS system ground.
2. I measure zero ohms between External power connector ground and Com3 ground. That means External power gnd is connected to system ground.
3. I measure 34 k ohm between pin 1 of ribbon cable (which is connected to battery ground) and BMS system ground with ohm probe leads in one direction and meter reads an open with leads in opposite position. There appears to be a semiconductor between these two grounds.
Also, the description of plug is EXTERNAL power. External means power coming from an isolated power source.
Solarfun4jim
Solar seduced :-)
@Cal
Please forgive my stupidity/lack of knowledge, but what does the Com3 port have to do with the seperate dc input socket on the other side of the unit? If the power from the battery pack was run through a SSR (which was itself powered by the LVD relay on the BMS), ie on a low voltage disconnect situation, it would also shut down the power to the BMS, thus preventing this parasitic load from depleting the battery pack any further?
I find all this stuff fascinating, but difficult to get a proper grasp of.....so not a critisism, just me trying to understand.
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Solarfun4jim
Solar seduced :-)
What does Com 3 have to do with this situation? Com3 is part of my answer to JoeHam regarding how I know that external power port ground is not equal to battery ground. Furthermore Chargery informed me months ago that they should not be directly connected together.
As to your second question, if you were to power the BMS using the External power plug, and receiving power from the battery-under-supervision then you need to connect the power wire before the disconnect relay or SSR. If you connect BMS power down stream of the relay then BMS will never get power back up once the relay trips.
Solarfun4jim
Solar seduced :-)
Thanks cal. Yes i knew it would get interesting if the disconnect closed down the BMS, but thought it might be better to protect the battery pack at all costs and rewire the relay for restart afterwards.
Your inputs are greatly appreciated.
I have emailed Jason Wang to see if he has any recommendations. If he answers my mail, i will report back...but i think the chap is busy busy.
Solarfun4jim
Solar seduced :-)
Got a reply from Jason....
"Power BMS using the sensing wires don't affect the BMS work normally. It is isolated internal of BMS, if power by bms by 24V battery but using separate cable, it has same result.
need not do this as you suggested."
I've made Jason aware of this conversation....he might want to comment, but i dont know.
So, im really no further forward. On a RV, how does one achieve an external power supply which is isolated? Any AC adapter connected 24/7 is going to get rather hot. :-(
"Power BMS using the sensing wires don't affect the BMS work normally. It is isolated internal of BMS, if power by bms by 24V battery but using separate cable, it has same result.
need not do this as you suggested."
I've made Jason aware of this conversation....he might want to comment, but i dont know.
So, im really no further forward. On a RV, how does one achieve an external power supply which is isolated? Any AC adapter connected 24/7 is going to get rather hot. :-(
Actually, I think a few people have connected battery ground to BMS ground with no know ill effects.
https://diysolarforum.com/threads/chargery-rs232-interface.3469/
https://diysolarforum.com/threads/chargery-bms-communications.5905/
In the past, I connected Com3 ground to battery ground before discovering there's a voltage difference of 330 mV between the two grounds. That lead to a discussion with Chargery. I now have an opto isolator connected to Com3.
This is another example of Chargery below par circuit design and documentation.
1. Using voltage sense wires to power the system including up to 3A loads.
2. Not using battery ground for BMS ground.
3. No documentation explaining Com3 and external power grounding limitations.
Following along,
I was leaning towards possibly using a Chargery BMS in a new lithium marine system I'm putting together, but this seems like a bit of a problem to some degree for any install, but especially off grid installs (RV, Boat, etc).
If I'm following this conversation properly there are 3 options for powering the BMS:
1) Power Chargery BMS via voltage sensing wires - not ideal and results in incorrect / inaccurate measurements
2) Power Chargery BMS via the onboard 12v system via a 12v to 15v+ DC Buck/Boost converter - sounds like there are concerns here with grounds
3) Power Chargery BMS via an AC Adapter - so 12v system -> Inverter -> AC/DC Converter -> BMS ... seems pretty silly, and BMS will shut down and not come back up if a disconnect event happens.
Would love more clarification here.
I was leaning towards possibly using a Chargery BMS in a new lithium marine system I'm putting together, but this seems like a bit of a problem to some degree for any install, but especially off grid installs (RV, Boat, etc).
If I'm following this conversation properly there are 3 options for powering the BMS:
1) Power Chargery BMS via voltage sensing wires - not ideal and results in incorrect / inaccurate measurements
2) Power Chargery BMS via the onboard 12v system via a 12v to 15v+ DC Buck/Boost converter - sounds like there are concerns here with grounds
3) Power Chargery BMS via an AC Adapter - so 12v system -> Inverter -> AC/DC Converter -> BMS ... seems pretty silly, and BMS will shut down and not come back up if a disconnect event happens.
Would love more clarification here.
Chargery's reply is not true!
What's going on here? This is not politics where anything goes. Statements like that are easily proven false.
Powering BMS using sense wires does affect cell voltage measurements.
I just connected a lab power supply to the external power connector. At 15V, supply current is 110 mA with BMS display active. Current drops to 68 mA with display off. Measurements are taken with an active display.
Cell--- Fluke------int powr------ext power
1------ 3.330 ----- 3.312 ------- 3.330
2------ 3.330 ----- 3.332 ------- 3.331
3------ 3.330 ----- 3.330 ------- 3.330
4------ 3.329 ----- 3.318 ------- 3.331
With external power there are no measurement errors associated with cell1 1 & 4.
There clearly is a measurement error when using the sense wires to power the BMS. Cell 4 is low by more then 10 mV. This error is caused by only 110 mA. If two relays combined draw 1A, then measurement error could be 100 mV.
Sounds like you're a glutton for punishment.
You realize there are other issues with Chargery? Chargery chose to disregard any current measurements in the range between -1A and +1A. Current in that range are recorded as 0A. This results in the SOC meter being way off base. Chargery is working on a new design that hopefully eliminates the SOC error. One of my goals starting this thread is to notify them of the cell voltage measurement error. But you know, any competent circuit designer would know right off the bat that this design does not provide accurate cell voltage measurements.
As for your questions, the simplest solution is to connect the battery output directly into the aux power input. The question remains, what about the ground issue. I would like to know, circuit wise, exactly what's affected. What are the ramifications tying the two grounds together.
Otherwise an isolated dc/dc would work. 24V in, 15V isolated out dc/dc
I haven't found an isolated dc/dc that works with a 13V battery.
There are other options out there. I haven't tested it but believe an Electrodacus would be an excellent choice.
grizzzman
Photon Vampire
- Joined
- Sep 21, 2019
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I have to say I "TOTALY" agree with you Cal.Chargery's reply is not true!
What's going on here? This is not politics where anything goes. Statements like that are easily proven false.
Powering BMS using sense wires does affect cell voltage measurements.
I just connected a lab power supply to the external power connector. At 15V, supply current is 110 mA with BMS display active. Current drops to 68 mA with display off. Measurements are taken with an active display.
Cell--- Fluke------int powr------ext power
1------ 3.330 ----- 3.312 ------- 3.330
2------ 3.330 ----- 3.332 ------- 3.331
3------ 3.330 ----- 3.330 ------- 3.330
4------ 3.329 ----- 3.318 ------- 3.331
With external power there are no measurement errors associated with cell1 1 & 4.
There clearly is a measurement error when using the sense wires to power the BMS. Cell 4 is low by more then 10 mV. This error is caused by only 110 mA. If two relays combined draw 1A, then measurement error could be 100 mV.
You may be right haha.
The fact of the matter is there is no 'perfect' solution, partially because everyone's needs and ideas of what a BMS should be are different.
I personally don't care about SOC meter within the BMS since I will be doing that externally, I'm most concerned with the ability to have accurate per-cell (and total) voltage measurements, the ability to protect the battery by way of Relays/Contactors, and data/communications that can be used outside the BMS, I thought the Chargery ticked those boxes in an affordable package but this thread brought up concerns for sure.
Bob B
Emperor Of Solar
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The luster has definitely worn off of Chargery. Mine is doing what I need it to do ... but I don't think at this point that I could recommend them.
While it was good they listened to us and came out with the DCC solution, there were serious problems with the design of the power connections to them ... and I still don't think they have made provisions for mounting them ... and significant problems have been reported with the pre-charge circuit.
I will be wanting to see some major improvements in the new models that are in design, but if they aren't willing to acknowledge the problems they have in their current design, I am concerned that the new ones will have problems as well.
I have been resisting getting up to speed on the ElectroDacus because I have been concerned that the product is totally dependent on 1 person. In my early work career, I worked for a business that was totally dependent on 1 person .... Things fell completely apart when he died .... lesson learned.
Now that there is an approved knock-off hitting the market ... I am actually more interested than before since it is no longer a 1 person operation.
While it was good they listened to us and came out with the DCC solution, there were serious problems with the design of the power connections to them ... and I still don't think they have made provisions for mounting them ... and significant problems have been reported with the pre-charge circuit.
I will be wanting to see some major improvements in the new models that are in design, but if they aren't willing to acknowledge the problems they have in their current design, I am concerned that the new ones will have problems as well.
I have been resisting getting up to speed on the ElectroDacus because I have been concerned that the product is totally dependent on 1 person. In my early work career, I worked for a business that was totally dependent on 1 person .... Things fell completely apart when he died .... lesson learned.
Now that there is an approved knock-off hitting the market ... I am actually more interested than before since it is no longer a 1 person operation.
D
Deleted member 9967
Guest
@Solarfun4jim Ok so the power supply [batteries or wall or solar] GIVES the device the voltage.
However the device [BMS, toaster or whatever] TAKES the amps it needs.
So you only have to know what the power supply gives to the device voltage wise and if it has enough amps to power the device.
Does this help?
trying to simplify it for you.
However the device [BMS, toaster or whatever] TAKES the amps it needs.
So you only have to know what the power supply gives to the device voltage wise and if it has enough amps to power the device.
Does this help?
trying to simplify it for you.
grizzzman
Photon Vampire
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Alex is sending me a "Green" ElectroDacus" SBMS40. I have been reading up on it. It appears to be a good fit for my system. I will do a write-up on the unit during the build.
Steve_S
Offgrid Cabineer, N.E. Ontario, Canada
I've ordered some of thee below to try a few things.
I am running BMS8T, so plan 1 is to power from NEG & POS off the battery terminals feeding to the BMS.
I am running BMS8T, so plan 1 is to power from NEG & POS off the battery terminals feeding to the BMS.
Solarfun4jim
Solar seduced :-)
Jason came back to me once more and suggests a diode on the negative side as follows...
and the comment..."check the cell voltage reading without external battery, then with external battery, check the difference."
Any of you electronics folks suggest an ideal diode for this purpose ?
and the comment..."check the cell voltage reading without external battery, then with external battery, check the difference."
Any of you electronics folks suggest an ideal diode for this purpose ?
Steve_S
Offgrid Cabineer, N.E. Ontario, Canada
This thread went from Voltage Accuracy to RS232 Coms and now - maybe cause I'm only on Mugga One - I'm confuddled. Add diode to what exactly ? Power input or RS232 ?
BTW: The Docs are only as good as the Information I was provided by @Chargery (Jason). Clearly I was NOT provided with all the information and therefore the ommissions in any Chargery Docs aren't my fault.
IF Anyone is inclined to help improve the docs / info, I may be able to add it in future docs or as an addendum of sorts.
IF SO, Send me a Private Message (Start Conversation) with the Title of "Chargery Doc Update" so I can keep track to compile the collected info.
Points at issue (power related):
- How to provide "External Power" from the battery pack ? (wired from (+) & (-) battery terminals)
-- ? For 12V Battery, is there recommended minimum Boost Converter.
-- ? Can the BMS8T be directly wired for external power from its 24V battery pack ?
-- ? Can the BMS16T from 48V ? Do we need to use a Step-down Converter.
-- ? BMS24T ??
Solarfun4jim
Solar seduced :-)
Sorry steve, i should have made clear...this was jasons reply purely on how to connect my 24v battery pack directly to the dc input(external) socket.
EDIT....clarification from Jason below
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