Chargey DCC surge protection.

[Ai4px]

I’ve read the manuals I can find on the chargery site and I’ve searched the forum here... I must be missing it.... can someone tell me the correct power up sequence? I imagine I turn on my intverters‘ breakers first, then power up the BMS which turns on the DCC... and I expect the DCC will limit current for hte first few seconds via a duty cycle. Is this correct?

 

[Steve_S]

Battery / BMS should be ON first, then the Inverter. The DCC allows for precharge out for the inverter before allowing full power. I have had no issue with this BUT I am also running 4 Packs in parallel, each with a 300A DCC. I can "Cold Start" my Samlex EVO 4024 which has a huge initial pull for a second to charge its capacitors. Some people have had issues but from what I can tell it's more configuration-related. I MUST SAY, I never tried to "Cold Start" the inverter with only one pack online, guess that's going to be tested in the next Test Cycle after that last battery bank update is done.

Cold Start meaning, the Batteries cutoff and inverter completely drained and forced off. I have done this through my Thrash Testing Cycles when I was doing the reliance tests. I am rural, remote and 100% offgrid so I needed to know the extremes & limits of my systems in a controlled way so I know what to expect in various situations should they arise.

I really get a laugh out of the "Precharge with a resistor before hooking up your wires" thing. Slight bit of ridiculous.
Joe Offgrid happily using his power and doing his thing. Batteries cutoff due to LVD (Low Volt Disconnect).
- Does Joe have to run to the Solar System, disconnect the wire, precharge the inverter & reconnect when he recharges the batteries ?
- The SCC kicks on and charges the batts but the Inverter can't be restarted because there is no dude with a Resistor to pre-charge it ?


Some Ref Info:

Li-Ion BMS - Precharge

Inverter Pre-Charge Circuit Inrush Current

PTC thermistors prevent damage to inverters with pre-charge circuits by reducing inrush current. Application notes and calculations.

www.ametherm.com

 

[Ai4px]

I just got a response from Jason of Chargery and this is what he said....
"first power on inverter and charger, then turn on DCC. DCC must be turned on finally, so the DCC will avoid spark, on DCC, A and B terminal has not difference, the current can flow A to B or flow B to A."

It makes sense to me that the DCC when first enabled would do current limiting.

 

[DerpsyDoodler]

I’ve read the manuals I can find on the chargery site and I’ve searched the forum here... I must be missing it.... can someone tell me the correct power up sequence? I imagine I turn on my intverters‘ breakers first, then power up the BMS which turns on the DCC... and I expect the DCC will limit current for hte first few seconds via a duty cycle. Is this correct?

I’m pretty sure the manual does state it, and I’m pretty sure there is a thread about it here somewhere cause I’ve read it. @Steve_S may be able to tell you from memory.

 

[cinergi]

Here's a piece of the discussion that occurred back in December: https://diysolarforum.com/threads/c...v-25-2020-ver-4-02-firmware.15122/post-173385

So I'll re-iterate -- the DCC does not have a proper precharge circuit. I still don't know how it actually works; if there is a precharge resistor, then you should be able to measure full battery voltage through the DCC even when its power switch is turned off. Even if that ends up being true, it will ONLY work when you physically move the switch from off to on. It does not precharge if the BMS has turned off the DCC for any reason.

I harp on this because I blew 2 300 amp class t fuses as a result of this improper precharge feature AND because I did find myself in a situation where there was full battery voltage despite the DCC being off (electrocution hazard even if the battery is powered down). I probably damaged one or both of my DCC's, as well. I haven't gone back and thoroughly vetted them because I gave up on them.

 

[Ai4px]

Here's a piece of the discussion that occurred back in December: https://diysolarforum.com/threads/c...v-25-2020-ver-4-02-firmware.15122/post-173385

So I'll re-iterate -- the DCC does not have a proper precharge circuit. I still don't know how it actually works; if there is a precharge resistor, then you should be able to measure full battery voltage through the DCC even when its power switch is turned off. Even if that ends up being true, it will ONLY work when you physically move the switch from off to on. It does not precharge if the BMS has turned off the DCC for any reason.

I harp on this because I blew 2 300 amp class t fuses as a result of this improper precharge feature AND because I did find myself in a situation where there was full battery voltage despite the DCC being off (electrocution hazard even if the battery is powered down). I probably damaged one or both of my DCC's, as well. I haven't gone back and thoroughly vetted them because I gave up on them.

I think what the DCC does is a high frequency duty cycle at power up. This has the effect of limiting current flow to very short spikes, effectively simulating the precharge resistor.
You are making me think that I can’t trust it, I may end up using a lightbulb as a pre-charge resistor. That way I can see the current flow and see when the capacitors are charged

 

[DerpsyDoodler]

Here's a piece of the discussion that occurred back in December: https://diysolarforum.com/threads/c...v-25-2020-ver-4-02-firmware.15122/post-173385

So I'll re-iterate -- the DCC does not have a proper precharge circuit. I still don't know how it actually works; if there is a precharge resistor, then you should be able to measure full battery voltage through the DCC even when its power switch is turned off. Even if that ends up being true, it will ONLY work when you physically move the switch from off to on. It does not precharge if the BMS has turned off the DCC for any reason.

I harp on this because I blew 2 300 amp class t fuses as a result of this improper precharge feature AND because I did find myself in a situation where there was full battery voltage despite the DCC being off (electrocution hazard even if the battery is powered down). I probably damaged one or both of my DCC's, as well. I haven't gone back and thoroughly vetted them because I gave up on them.

@Chargery

Perhaps we should late Jason answer to that again, then. He has responded to that statement before and explained how it works.

 

[cinergi]

@Chargery

Perhaps we should late Jason answer to that again, then. He has responded to that statement before and explained how it works.

Yup the explanations are in the quoted thread. And he said precharge only works when switching from off to on. One should be able to verify the off-to-on behavior by measuring full battery voltage though the DCC while it's off (because it's connected through a resistor). If the BMS has instructed the DCC to be off (and the DCC switch is on), then you should observe NO voltage through the DCC.

 

[DerpsyDoodler]

Yup the explanations are in the quoted thread. And he said precharge only works when switching from off to on. One should be able to verify the off-to-on behavior by measuring full battery voltage though the DCC while it's off (because it's connected through a resistor). If the BMS has instructed the DCC to be off (and the DCC switch is on), then you should observe NO voltage through the DCC.

I didn’t understand it like that. I understood it to mean that the device (DCC) had to be powered on and under control of the BMS for precharging to work. For instance, if discharge was enabled, and you attached the inverter as load, you’d get a spark (and inrush). However, if you had discharge disabled (by the BMS) and attached your load (inverter), then enabled discharge on the BMS. Precharge would work, and there would be no inrush. I have not been able to verify this myself, yet. But when I get my chargery BMSs, I’ll be happy to report back on it. Furthermore, I will just ask Jason, as part of another question before I purchase. Quite certain i understood him correctly, though.

 

[cinergi]

I didn’t understand it like that. I understood it to mean that the device (DCC) had to be powered on and under control of the BMS for precharging to work. For instance, if discharge was enabled, and you attached the inverter as load, you’d get a spark (and inrush). However, if you had discharge disabled (by the BMS) and attached your load (inverter), then enabled discharge on the BMS. Precharge would work, and there would be no inrush. I have not been able to verify this myself, yet. But when I get my chargery BMSs, I’ll be happy to report back on it. Furthermore, I will just ask Jason, as part of another question before I purchase. Quite certain i understood him correctly, though.

Yeah, the English is difficult to parse -- but it became clear to me there's no precharge once the DCC is physically switched on after I told him it's not a proper precharge desgin and I suggested that it have a timer circuit to have the resistor on first and then fully connect the FETs. He said "oh, good idea!" (paraphrase) ... that plus me observing (and HEARING!) the effect of turning on the DCC (and blowing 2 fuses) was a very clear indication that there's no precharge.

 

[DerpsyDoodler]

Yeah, the English is difficult to parse -- but it became clear to me there's no precharge once the DCC is physically switched on after I told him it's not a proper precharge desgin and I suggested that it have a timer circuit to have the resistor on first and then fully connect the FETs. He said "oh, good idea!" (paraphrase) ... that plus me observing (and HEARING!) the effect of turning on the DCC (and blowing 2 fuses) was a very clear indication that there's no precharge.

What version of the firmware did you have? There’d been a lot of updates around all that thread. I think I will wait to make a judgement till he gets back to me explaining it. I’ll be happy to post the results of the email conversation.

 

[cinergi]

What version of the firmware did you have? There’d been a lot of updates around all that thread. I think I will wait to make a judgement till he gets back to me explaining it. I’ll be happy to post the results of the email conversation.

It was 4.01. As far as I know, it's a hardware change to implement the proper precharge -- but would love to see a solid update and testing/verification from someone.

 

[Chargery]

I didn’t understand it like that. I understood it to mean that the device (DCC) had to be powered on and under control of the BMS for precharging to work. For instance, if discharge was enabled, and you attached the inverter as load, you’d get a spark (and inrush). However, if you had discharge disabled (by the BMS) and attached your load (inverter), then enabled discharge on the BMS. Precharge would work, and there would be no inrush. I have not been able to verify this myself, yet. But when I get my chargery BMSs, I’ll be happy to report back on it. Furthermore, I will just ask Jason, as part of another question before I purchase. Quite certain i understood him correctly, though.

the DCC oprate instruction is as below, upon the instructions, the pre-charge will work,
first step, turn off DCC , connect DCC to inverter or/and charger, DCC precharge inverter or/and charger
second step, turn on DCC, the DCC will be closed if without any warnings on BMS.
third step, turn on inverter and charger, battery will discharge or being charged. inverter/load control discharging current, charger control charging current. when any cell voltage reach UVP setting, BMS cut off discharge by OPEN DCC automatically, when any cell voltage reach OVP setting, BMS cut off charge by OPEN DCC automatically.

 

[DerpsyDoodler]

Here is Jason/Chargery’s email response to the question ”How does the DCC control in-rush current?”. Copy and pasted directly from the email.

“when DCC turn off, battery pre-charge charger or inverter through resistors that restrict the surge current and sparks.
when DCC turn on, the resisrors is be short circuit. charging current and discharge current don't flow the resistors.
so DCC must be turned on finally .”

So with that said, there is a precharge circuit, and it does work. Perhaps your unit was brought prior to them adding it from the feedback in this forum?

 

[cinergi]

Here is Jason/Chargery’s email response to the question ”How does the DCC control in-rush current?”. Copy and pasted directly from the email.

“when DCC turn off, battery pre-charge charger or inverter through resistors that restrict the surge current and sparks.
when DCC turn on, the resisrors is be short circuit. charging current and discharge current don't flow the resistors.
so DCC must be turned on finally .”

So with that said, there is a precharge circuit, and it does work. Perhaps your unit was brought prior to them adding it from the feedback in this forum?

Pre-charge ONLY works if you physically turn the switch from off to on. It does not work if the BMS instructs the DCC to turn off and then on again. I used the switch to turn on the DCC and I still blew a fuse (maybe their resistor is too small -- either wrong resistance value or can't handle the heat). It's also ridiculous that even with the DCC switch off, it is "always on" with a resistor which means your battery terminals are always live and there's always current flowing into your system.

A proper pre-charge circuit means:
1) When the relay is off (either via external switch or BMS told it to shut off), there is no voltage at the battery terminals
2) When the relay (solid-state or otherwise) is to be activated, a separate circuit with a resistor is first activated for a period of time and THEN the main relay is turned on
3) The resistor is then removed from the circuit
4) If the relay is turned off for any reason, there is no voltage at the terminals

This is the only way to have a safe pre-charge. Chargery's version is a shock hazard and does not cover the case when the BMS turns the relay on (e.g. after recovering from a HVD event).

 

[DerpsyDoodler]

Bahhhhhhhhhh......you....wha...must....resist....conversion......

your logic and reasoning is strong.
ok ok....so what do you think about the idea of having 1 shunt per BMS? Is that excessive? Or a good use of shunts?

 

[cinergi]

Bahhhhhhhhhh......you....wha...must....resist....conversion......

your logic and reasoning is strong.
ok ok....so what do you think about the idea of having 1 shunt per BMS? Is that excessive? Or a good use of shunts?

Assuming that 1 per BMS also means 1 per battery and you're implying multiple batteries .. I wouldn't say it's required per-se but me personally I'd want to know the SoC's of each battery. I'd probably have an extra shunt in front of all the batteries so I can see the overall current and SoC.

 

[Ai4px]

OK, I fired my new battery up today.... I learned that the LAST thing you turn on is the DCC contactor. By turning it on, I mean the manual flip switch. It nicely limited the current going to my two Sunny Islands. So later in the day I’m mucking around with the settings on the BMS and forced it to turn off the DCC as if the battery voltage was too low. When it powered up the DCC again, there WAS NO softstart. This is crazy... They really need to implement the softstart so that it works when the DCC has been commanded off.

I’m talking about inrush current so severe that my cables jumped on the bench due to magnetic flux field.

 

[Bob B]

OK, I fired my new battery up today.... I learned that the LAST thing you turn on is the DCC contactor. By turning it on, I mean the manual flip switch. It nicely limited the current going to my two Sunny Islands. So later in the day I’m mucking around with the settings on the BMS and forced it to turn off the DCC as if the battery voltage was too low. When it powered up the DCC again, there WAS NO softstart. This is crazy... They really need to implement the softstart so that it works when the DCC has been commanded off.

I’m talking about inrush current so severe that my cables jumped on the bench due to magnetic flux field.

We haven't heard from @Chargery since the start of the Chinese new year .... so, I'm not sure what is going on with them ..... but, I totally agree with you on this.
The soft start should work when it is powered up .... and when it is commanded from off to on.

 

[eumobong]

Pre-charge ONLY works if you physically turn the switch from off to on. It does not work if the BMS instructs the DCC to turn off and then on again. I used the switch to turn on the DCC and I still blew a fuse (maybe their resistor is too small -- either wrong resistance value or can't handle the heat). It's also ridiculous that even with the DCC switch off, it is "always on" with a resistor which means your battery terminals are always live and there's always current flowing into your system.

A proper pre-charge circuit means:
1) When the relay is off (either via external switch or BMS told it to shut off), there is no voltage at the battery terminals
2) When the relay (solid-state or otherwise) is to be activated, a separate circuit with a resistor is first activated for a period of time and THEN the main relay is turned on
3) The resistor is then removed from the circuit
4) If the relay is turned off for any reason, there is no voltage at the terminals

This is the only way to have a safe pre-charge. Chargery's version is a shock hazard and does not cover the case when the BMS turns the relay on (e.g. after recovering from a HVD event).

If one put a limiting resistor of say 100W 30ohms across the terminal of the DCC, will it solve this problem?

What will be the likely issues with doing that?