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diy solar

Checking Chargery voltage measurements

grizzzman said:
I would defiantly recommend the diode. I had the external power off but connected to the the BMS. I hooked up a 25 amp load to the off side (on the ground side of the contactor) and was surprised when the load came on. The U1 chip in the BMS is Toast. With the DC to DC connected but not powered, For a short time tried pulling 25 amps. unplugged when i saw smoke. At least the battery side still works

@Solarfun4jim I found that the ISDT BATTGO BG-8S is very accurate.​

Click to expand...
I have looked at their products they have a T8 that would balance at 2.2amp per cell that I wasn't sure how it would work out.
 
Solarfun4jim said:
@JoeHam
Thanks Joe,
I'm totally inexperienced in electrics....so how would you connect the external power input to the battery pack to provide the required 3A
I just assumed you needed the converter to regulate the current to the required 3A???The external power input the the BMS is just fine at 24v. Its within the specification. As far as the 3amp specification, the supplying source only needs to supply up to 3A and much less for a system with a DCC. A LOAD , in this case the BMS will only draw what is needed.
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Steve_S said:
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.

2.1mm_x_5.5mm_barrel_type_male_dc_power_jack_adapter_connector.jpg
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@Steve_S
Hi steve, just looking for confirmation that you have now used these on the chargery main board input, powered directly from your 24v pos & neg terminals? I assume no mishaps, no complications with mixed grounds and no diodes needed?
Thanks.
 
Chargery said:
please visit https://diysolarforum.com/threads/c...te-nov-25-2020-ver-4-02-firmware.15122/page-5 Bob finished the testing, the BMS is powered by battery with external power port.
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@Chargery
Thanks for the link jason, however i believe bob is using a 4s 12V system with a shottky diode, where as i'm looking for info as regards a 24V system without the diode. If all thats needed is a simple 5A fuse on the positive connection, then that would be fine.
I had thought i'd read somewhere that the 24V battery ground was not compatible with the DC input plug ground, however i dont fully understand this.
 
Solarfun4jim said:
@Chargery

I had thought i'd read somewhere that the 24V battery ground was not compatible with the DC input plug ground, however i dont fully understand this.
Click to expand...

Same question here and I believe the manual says you can power with up to 60v.

A good time for @Chargery to clarify if you can power the Chargery directly from a 24 or 48v nominal battery.

Is it permissible?

Is it a good way to improve accuracy??
 
From my vault of e-mail exchanges with Jason:

NEW BMS’ Extra item to include or have available I the store, it people are going to use External Power they need an adapter for it, either include it or have it on the website. These I believe are ideal, I just received mine so that I can power the BMS from the battery packs own (+) & (-) rather than take the power from the harness. an adapter is easy to get, but add a diode is a trouble, so i don't suggest all users do this on all BMS modles.

Should there be a “filter” or anything extra between this plug & the batteries own +/- ? don't need filter, but a diode is essential.

for the problem, i make many testing with 4S and 8S battery on BMS8T, 16S battery on BMS16T, the testing result is only "power BMS by external socket from 4S battery at 12V" is useful or can avoid the influence of current flow harness. because the current from battery is maximum when 4S battery at 12V. so i don't think it is not essential for other battery or BMS. the root solution is power BMS by AC/DC adapter or by other battery. When power by AC/DC adapter, the cell voltage is very accurate, it is tested by CAL on forum, in fact, when we calibrate cell voltage, the BMS is powered by AC/DC adapter.

As far as cell voltage accuracy, it depends on cell voltage calibration, when calibrate again, the cell voltage reading is improved. power BMS by external socket don't solve the problem. we improved the reference voltage accuracy and changed the cell voltage accuracy testing method after calibration two months ago. now the cell voltage reading is acceptable, it is under 5mv difference compared with FLUKE reading.

as far as current reading, your suggestion is correct, the battery positive and negative cable should be together and short as soon as possible. we updated the current measurement on V4.02, The accuracy is improved, but if it is not stable, need change or add a low pass filter inside of BMS, for different charger, inverter, and cable distance, length, have not perfect solution to solve all problems.
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12V off battery terminals apparently need the Shotky resister,
24V up should be ok, from what is gleened. I have asked for a very clear response like for 12V do this, 24V, 48V fo A or B... nope.

I want to put the packs on Batt Terminal power and have the adapters for the plugs. It occured to me though, it may be prudent to put an ON/OFF switch between the plug in and the terminal connection to kill power without having to pull the plug.

1607523625663.png
 
Steve_S said:
From my vault of e-mail exchanges with Jason:



12V off battery terminals apparently need the Shotky resister,
24V up should be ok, from what is gleened. I have asked for a very clear response like for 12V do this, 24V, 48V fo A or B... nope.

I want to put the packs on Batt Terminal power and have the adapters for the plugs. It occured to me though, it may be prudent to put an ON/OFF switch between the plug in and the terminal connection to kill power without having to pull the plug.

View attachment 29765
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I thought i might just put an inline blade fuse of 5A, that way if i want to kill the power i just pull the fuse, plus a little protection also.

If you had to go down the route of an AC adapter, which ones would be recommended for connection 24/7/365 without overheating? Even the best laptop bricks get very warm when used for a few hours.
 
There's also measurement errors with 24V batteries. The magnitude of the error is dependent on how much current the disconnect devices draw. If you use mechanical relays then you will see significant errors. The best remedy is to use external power input along with the Schottky diode.
 
Cal said:
There's also measurement errors with 24V batteries. The magnitude of the error is dependent on how much current the disconnect devices draw. If you use mechanical relays then you will see significant errors. The best remedy is to use external power input along with the Schottky diode.
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Cheers Cal, but on a 24V RV system, you don't really have external power in the true sense of the word. I believe i read somewhere that if powering the 'DC input' connection from the 24V battery pack, then you would not need the schottky diode. The diode is only necessary for 12V systems, but happy for you to correct me on this. If you power an AC adapter from the inverter, then in reality, it is not truly an external power input. We seem to be going around in circles.
 
Not true. It doesn't matter what size the battery pack is (12V or greater), you absolutely need a schottky diode.

You don't need the diode if the external supply is isolated from battery (no common ground connection).
 
To tell the truth, I'm not really sure what the Schottky diode does in this application .... but since it was indicated in the manual I went ahead and installed it on the 4S pack. They are cheap and it was pretty easy to install.

Can someone explain why it would be desirable on a 12V pack ... but not on a 24 or 48? What is the purpose of the diode?

I do know that the Chargery BMS will have to down regulate power of 24V or higher. Might be easier to just use an external DC-DC converter to down regulate the voltage and take that heat load out of the BMS.
 
Cal said:
Not true. It doesn't matter what size the battery pack is (12V or greater), you absolutely need a schottky diode.

You don't need the diode if the external supply is isolated from battery (no common ground connection).
Click to expand...

@Cal
Right Cal, now we are getting somewhere (y)

Im presuming the same 40v 3A schottky diode will do for the 24v DC connection?

What im trying to ascertain, is, if you have the 24V pack as the only power source, what is the most efficient way of connecting it to the BMS to acheive the greatest possible voltage accuracy? Direct seperate connections (not harness wires) with an inline fuse and schottky diode?

Appreciate your input.

edit ps...i'm not interested in SOC or balance function of BMS, only really accurate voltage measurement.
 
Solarfun4jim said:


What im trying to ascertain, is, if you have the 24V pack as the only power source, what is the most efficient way of connecting it to the BMS to acheive the greatest possible voltage accuracy? Direct seperate connections (not harness wires) with an inline fuse and schottky diode?

[/QUOTE]
Before you do anything else, you need to check if you really need to swap power source. Is cell 1 consistently lower? Does cell 1 voltage drop when you activate the display? You may be OK, it depends on how much current the disconnect devices take.

To use external power, add 2 new wires connected to the battery. One to ground, the other to the 24V output. Connect the diode to the ground lead. You can add a fuse if you want. Sizing the fuse is tricky. It depends on how much current the disconnect devices take. You can measure the current using a multimeter (with amp jacks). Current may be around 100 mA to 500 mA. Whatever you measure, I would double that for the fuse rating.
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Hello all, this is my first post on this forum. I was looking for info regarding voltage measurement. That because my measurements are of at almost 100mV. Way to much off course. What I did so far to see where the problem is:

  1. Checked the balance leads in 2 ways, measured resistance from battery connection to BMS connector and measured the voltage with my multimeter. Direct on battery and via the wire. All ok.
  2. Torqued the busbars.
  3. Updated firmware to version 4.03 (BMS) and 4.02 (LCD).
  4. Gave the BMS external power.
None of this made a difference. Also I found out the BMS can not be calibrated in terms of voltage at cell level. That is a terrible thing!

The BMS is a 16T, 1 year old but was laying on the shelf waiting to be installed. That moment was yesterday. The battery is a DIY 16s3p LiFePO4 bank 618 Ah.

Is there anything else I can try? Or did I just buy a piece of shit?

Regards, Rik
 
Bob B said:
Can someone explain why it would be desirable on a 12V pack ... but not on a 24 or 48? What is the purpose of the diode?
Click to expand...

The diode is here because for a mysterious reason the BMS logic ground isn't at the same potential than (or isolated of) the power ground. As @Cal said it is desirable for all voltages, not just 12 V ;)
 
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