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Daly 250A, current (amperage) reading jumping/inaccurate/inconsistent

Martijn

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May 6, 2021
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235
Hi all,

I couldn't wake the Daly 250A (no fan) BMS up with a load on the battery, so I shorted B- and P- as per some videos/threads. Some sparks, but still no luck.

In the end, I used the two pins that can supposedly be connected to a button to restart the BMS.

It woke up.

However... I didn't notice it before so I'm not sure if it was caused by the short or not.

The current flow reading (amperage reading in the app or the PC software) is jumping all over the place.

According to the Victron shunt, it's currently charging with 39.5A - shunt connected at the P- side of the BMS.

Current reading on the PC software: -19, -67, -39, -23 etc. All over the place.

When discharging, the load is higher and so are the jumps, they're so high, that the 'over discharge protection' kicks in and the BMS shuts down.

Basically, I'm unable to use it (ignoring the capacity issues). I wonder if the internal measuring electronics could be damaged by shorting B- and P- (several times), even though I just touched it with a 2.5mm2 cable for a short while.

Any help appreciated.

With regards,

Martijn
 
Hi all,

I couldn't wake the Daly 250A (no fan) BMS up with a load on the battery, so I shorted B- and P- as per some videos/threads. Some sparks, but still no luck.

In the end, I used the two pins that can supposedly be connected to a button to restart the BMS.

It woke up.

However... I didn't notice it before so I'm not sure if it was caused by the short or not.

The current flow reading (amperage reading in the app or the PC software) is jumping all over the place.

According to the Victron shunt, it's currently charging with 39.5A - shunt connected at the P- side of the BMS.

Current reading on the PC software: -19, -67, -39, -23 etc. All over the place.

When discharging, the load is higher and so are the jumps, they're so high, that the 'over discharge protection' kicks in and the BMS shuts down.

Basically, I'm unable to use it (ignoring the capacity issues). I wonder if the internal measuring electronics could be damaged by shorting B- and P- (several times), even though I just touched it with a 2.5mm2 cable for a short while.

Any help appreciated.

With regards,

Martijn
Since you have a shunt you could just bypass the bms.
I assume you have a correctly sized fuse immediately off the positive terminal of the battery over-current protection.

I've seen at least one report where a Daly BMS came from the factory with some mis-configured values that made the current accounting wonky.

I will try to find the thread and link to it.
Not saying its the problem but it might be.
@HighTechLab found the fix, hope he chimes in.
 
Since you have a shunt you could just bypass the bms.
I assume you have a correctly sized fuse immediately off the positive terminal of the battery over-current protection.

I've seen at least one report where a Daly BMS came from the factory with some mis-configured values that made the current accounting wonky.

I will try to find the thread and link to it.
Not saying its the problem but it might be.
@HighTechLab found the fix, hope he chimes in.
Hi Joey,

Thanks for the reply. I'm not sure if I understand with regard to bypassing the BMS though.

From what I understood, the BMS is required to:
- monitor cell voltage (over/under voltage)
- monitor charge and discharge overcurrent
- monitor temperature

Perhaps I misunderstood you're post?

Yes, there's a fuse on the positive terminal and I'm using a Victron Multiplus II (and will add MPPT controllers later) for charging.
 
Hi Joey,

Thanks for the reply. I'm not sure if I understand with regard to bypassing the BMS though.

From what I understood, the BMS is required to:
- monitor cell voltage (over/under voltage)
- monitor charge and discharge overcurrent
- monitor temperature

Perhaps I misunderstood you're post?

Yes, there's a fuse on the positive terminal and I'm using a Victron Multiplus II (and will add MPPT controllers later) for charging.
Yeah my bad.
When you bypass the bms you need to do out of band signalling to control the charge sources and loads.
This works fine if your charge sources and loads support it.
Sometimes it can be hacked even if they don't but its a project for advanced users.
 
Yeah my bad.
When you bypass the bms you need to do out of band signalling to control the charge sources and loads.
This works fine if your charge sources and loads support it.
Sometimes it can be hacked even if they don't but its a project for advanced users.
Right, that sounds too advanced for me. This is my first 24V LifePo4 battery project. Seen tons of videos and read through the forum on how to build one, including the top balance etc.

Anyway, the Daly BMS is returning very different current-readings on every read-operation of the software. That can't be right.
 
Right, that sounds too advanced for me. This is my first 24V LifePo4 battery project. Seen tons of videos and read through the forum on how to build one, including the top balance etc.

Anyway, the Daly BMS is returning very different current-readings on every read-operation of the software. That can't be right.
Yeah sounds wonky.
A good test would be to turn off all charge sources and just discharge with one resistive load.
See if that bounces.
Report back.
Is the voltage also bouncing?
 
Yeah sounds wonky.
A good test would be to turn off all charge sources and just discharge with one resistive load.
See if that bounces.
Report back.
Is the voltage also bouncing?
I did several capacity tests (cells don't seem to be able to deliver as promised), using a heatgun at just under 1000W (via inverter, obviously), the shunt reported a charge of just over 40A, the BMS jumped. When I increased load to about 85A, the BMS jumped so far up and down, it ran into the high discharge protection set at a 175A limit.

Voltage is steady, no problems there.
 
Seller claims the inverter can interfere with the BMS, resulting in this behaviour. Does that make any sense to you?

I'm using a Victron MultiPlus II to get a 60A load.
 
Does this occur when the inverter is turned off ?
Can't do a 60A load when the inverter is turned off ;)

Test setup: 8 cells, Daly BMS, Victron inverter connected to battery plus and BMS P-

I now have a 6.1A 24V load, directly to the BMS/battery cables.

Inverter turned on, no external AC load:
- according to the Victron monitor, it's using about 1A.
- Bluetooth app displays load between 4.9 and 8.6A.

Inverter turned off:
- Bluetooth app displays load of 6.1-6.2A

So yes, it does appear the Victron inverter is causing issues here?!

Which begs the question: how can this interference be fixed?
 
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My Chargery dose the same thing it appears the inverter is taking bites of energy from the battery, not a constant current, the DC clamp on ammeter reads a constant current, perhaps the BMS has a higher sampling rate to improve accuracy, just speculation

Are the DC cables to the inverter twisted and isolated fom other wiring to reduce interference? The inverter may have a superimposed signal being fed into the DC, is the inverter sine wave and is it high or low frequency?
 
My Chargery dose the same thing it appears the inverter is taking bites of energy from the battery, not a constant current, the DC clamp on ammeter reads a constant current, perhaps the BMS has a higher sampling rate to improve accuracy, just speculation

Are the DC cables to the inverter twisted and isolated fom other wiring to reduce interference? The inverter may have a superimposed signal being fed into the DC, is the inverter sine wave and is it high or low frequency?
When I used the inverter to power a single load for testing, the reading the inverter and battery monitor (via shunt) returned where quite solid: close to 60A. The BMS returned values from about 10 to 150A. So I'm pretty sure the inverter itselfs draws a steady current. It certainly can't pull 150A when the external AC load is 1400-1500W.

The DC cables to the inverter are 50mm2 cables, not twisted cables, one appears to lie across the other though. What do you mean by 'isolated'? How do you suggest to reduce interference?

This is the inverter I'm using (24/3000/70-32 variant): https://www.victronenergy.com/inverters-chargers/multiplus-ii

Mind you, this is just a test setup: cells, BMS and inverter are sitting on a stone tile floor.
 
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Twisting the cables can reduce noise or ripple by cancelling superimposed signals, this is used in telephony to reduce cross talk as well a anti side ton induction coils for filtering, at least that is what was done before cellular phones, it is also used in computer cables. Google ripple and noise in conjunction with inverters, it's a heavy reading subject.

The inverter is good quality, just checking because there are so many cheap ones out there which are garbage.

My fluctuations are constant with the inverter draw, not as radical as what you describe, my suggestion is try the simple things first.
 
Twisting the cables can reduce noise or ripple by cancelling superimposed signals, this is used in telephony to reduce cross talk as well a anti side ton induction coils for filtering, at least that is what was done before cellular phones, it is also used in computer cables. Google ripple and noise in conjunction with inverters, it's a heavy reading subject.

The inverter is good quality, just checking because there are so many cheap ones out there which are garbage.

My fluctuations are constant with the inverter draw, not as radical as what you describe, my suggestion is try the simple things first.
I know twisted cables are used here and there in cars etc, but I never heard/seen about this for cables towards an inverter, as these are quite heavy.

Check the installation manual for the inverter, nothing about this particular subject in it either.

I can try and move the cables around a bit to see if that makes a difference, but once I have to put them into the camper, it will all be close to each other again, inverter, cables and BMS.

I can't imagine I'm the only one suffering from this, apparently you have it too. Currently, this issue makes the over current protection of the BMS useless, as the erroneous reading goes way up and triggers it while in actuality, the load is much less... :-(
 
Even high voltage transmission lines, 500 000V use regular transposition points to cancel out magnetically induced interference, both in AC and DC, if the inverter is actually taking intermittent bites out of the battery there would be a rising and collapsing magnetic field, because the negative and positive are connected directly to the BMS, it's possible for this corrupt the information the BMS is attempting to process.

The only way to see what's really going on is to use an oscilloscope, short of doing that it's all guesswork, but doing the basics first is the best approach. Ultimately it could be a Daly phenomenon, I'm guessing there is little in the way of support.
 
I want to jump in and confirm my 200a 16s Daly BMS has always done this as well. If I put a constant 100a load, I'll see it jump from 49a to 153a to 74a to 112a etc. But the SOC indicator is always spot on, and it has never shut down on me, so I just rely on my Victron Smart Shunt to give me immediate amp draw.

I'm interested to hear how this pans out, and am willing to test out a few things as well if it helps.
 
I want to jump in and confirm my 200a 16s Daly BMS has always done this as well. If I put a constant 100a load, I'll see it jump from 49a to 153a to 74a to 112a etc. But the SOC indicator is always spot on, and it has never shut down on me, so I just rely on my Victron Smart Shunt to give me immediate amp draw.

I'm interested to hear how this pans out, and am willing to test out a few things as well if it helps.
At first, I had a high discharge current set of 150A. When I was testing with a load near 90A, it jumped to 150+ (all the while, the shunt would register the correct current draw) and it triggered the disconnect. Basically, this behaviour means we cannot use the BMS for over (dis)charge protection.

Somehow, I feel a bit better knowing I'm not the only one.

But how to fix it?
 
If it is a battery line noise problem taping battery lines together to reduce their series inductance may help. It cuts down voltage ringing at inverter and bms ends of battery line. Also might try an air conditioner foil run cap at BMS end of battery lines.
 
This is normal behavior for most current-measuring devices when there's an inverter involved. I don't know the Daly settings but are you able to set the cutoff delay for when the max amperage is exceeded? e.g. > 150 amps for > 5 seconds or something?
I've seen the variation in Chargery, Victron Shunt (yup!), and Orion BMS (both the "instant" and "average" values), as well as some other threads on this forum about the same phenomenon. It's not noise. It's the 120HZ waveform induced into the DC system from the Inverter.
 
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