MPPT chargers dying upon battery disconnect?...

[Joerg]

Attention, this is one of those rare electronics-related questions

Will be rigging up a small power-failure backup system. Essentially a
12V LiFePO4 battery (with BMS in there), inverter, solar panels, MPPT
charger.

When reading up on stuff and talking to people I found something very
disconcerting. It seems that MPPT charge controllers can and often do
commit suicide when operated without a battery. It even says that in the
manuals a lot. The trigger event can be as simple as the BMS opening for
some reason and ... *PHUT* ... MPPT is gone. A friend had that happen,
twice.

They can also send out a substantial voltage spike or short their
MOSFETs during such events, the latter letting full solar panel voltage
onto the 12V power bus. Both of which can kill rather expensive gear
connected to the 12V bus.

Why is that? Are the engineers designing this stuff not very bright? I\'d
never release a design with such \"traits\".

Does anyone know lower-end MPPT charge controllers (20-40A range) that
are properly designed in this respect? Preferably ones that are also low
noise so they don\'t mess with measurements on the lab bench. The Genasun
brand is low noise but AFAICT they only come for very low solar panel
voltages.

Of course, one solution is to build a massive crowbar to blow a fuse and
protect the connected gear. The MPPT charger might possibly still die.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Fred Bloggs]

On Monday, January 30, 2023 at 1:40:50 PM UTC-5, Joerg wrote:

Attention, this is one of those rare electronics-related questions

Will be rigging up a small power-failure backup system. Essentially a
12V LiFePO4 battery (with BMS in there), inverter, solar panels, MPPT
charger.

When reading up on stuff and talking to people I found something very
disconcerting. It seems that MPPT charge controllers can and often do
commit suicide when operated without a battery. It even says that in the
manuals a lot. The trigger event can be as simple as the BMS opening for
some reason and ... *PHUT* ... MPPT is gone. A friend had that happen,
twice.

They can also send out a substantial voltage spike or short their
MOSFETs during such events, the latter letting full solar panel voltage
onto the 12V power bus. Both of which can kill rather expensive gear
connected to the 12V bus.

Why is that? Are the engineers designing this stuff not very bright? I\'d
never release a design with such \"traits\".

Does anyone know lower-end MPPT charge controllers (20-40A range) that
are properly designed in this respect? Preferably ones that are also low
noise so they don\'t mess with measurements on the lab bench. The Genasun
brand is low noise but AFAICT they only come for very low solar panel
voltages.

Of course, one solution is to build a massive crowbar to blow a fuse and
protect the connected gear. The MPPT charger might possibly still die.

I\'ve seen that as a warning, in the user\'s manual, even for those little solar battery maintainers to keep a seldom used car battery topped off.

You have to remove power to the MPPT charge controller before you remove the battery.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Joerg]

On 1/30/23 10:55 AM, Fred Bloggs wrote:

On Monday, January 30, 2023 at 1:40:50 PM UTC-5, Joerg wrote:
Attention, this is one of those rare electronics-related questions

Will be rigging up a small power-failure backup system. Essentially a
12V LiFePO4 battery (with BMS in there), inverter, solar panels, MPPT
charger.

When reading up on stuff and talking to people I found something very
disconcerting. It seems that MPPT charge controllers can and often do
commit suicide when operated without a battery. It even says that in the
manuals a lot. The trigger event can be as simple as the BMS opening for
some reason and ... *PHUT* ... MPPT is gone. A friend had that happen,
twice.

They can also send out a substantial voltage spike or short their
MOSFETs during such events, the latter letting full solar panel voltage
onto the 12V power bus. Both of which can kill rather expensive gear
connected to the 12V bus.

Why is that? Are the engineers designing this stuff not very bright? I\'d
never release a design with such \"traits\".

Does anyone know lower-end MPPT charge controllers (20-40A range) that
are properly designed in this respect? Preferably ones that are also low
noise so they don\'t mess with measurements on the lab bench. The Genasun
brand is low noise but AFAICT they only come for very low solar panel
voltages.

Of course, one solution is to build a massive crowbar to blow a fuse and
protect the connected gear. The MPPT charger might possibly still die.

I\'ve seen that as a warning, in the user\'s manual, even for those little solar battery maintainers to keep a seldom used car battery topped off.

You have to remove power to the MPPT charge controller before you remove the battery.

Yeah I know, and that really doesn\'t make sense in such a design. Any
Li-Ion battery can literally \"remove itself\" via BMS action. Any
external stuff should be resilient in that case and most MPPT chargers
seem not to be.

In medieval Europe they would have dunked the design engineer into a
moat several times for \"moral cleansing\"

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Fred Bloggs]

On Monday, January 30, 2023 at 2:48:21 PM UTC-5, Joerg wrote:

On 1/30/23 10:55 AM, Fred Bloggs wrote:
On Monday, January 30, 2023 at 1:40:50 PM UTC-5, Joerg wrote:
Attention, this is one of those rare electronics-related questions

Will be rigging up a small power-failure backup system. Essentially a
12V LiFePO4 battery (with BMS in there), inverter, solar panels, MPPT
charger.

When reading up on stuff and talking to people I found something very
disconcerting. It seems that MPPT charge controllers can and often do
commit suicide when operated without a battery. It even says that in the
manuals a lot. The trigger event can be as simple as the BMS opening for
some reason and ... *PHUT* ... MPPT is gone. A friend had that happen,
twice.

They can also send out a substantial voltage spike or short their
MOSFETs during such events, the latter letting full solar panel voltage
onto the 12V power bus. Both of which can kill rather expensive gear
connected to the 12V bus.

Why is that? Are the engineers designing this stuff not very bright? I\'d
never release a design with such \"traits\".

Does anyone know lower-end MPPT charge controllers (20-40A range) that
are properly designed in this respect? Preferably ones that are also low
noise so they don\'t mess with measurements on the lab bench. The Genasun
brand is low noise but AFAICT they only come for very low solar panel
voltages.

Of course, one solution is to build a massive crowbar to blow a fuse and
protect the connected gear. The MPPT charger might possibly still die.

I\'ve seen that as a warning, in the user\'s manual, even for those little solar battery maintainers to keep a seldom used car battery topped off.

You have to remove power to the MPPT charge controller before you remove the battery.

Yeah I know, and that really doesn\'t make sense in such a design. Any
Li-Ion battery can literally \"remove itself\" via BMS action. Any
external stuff should be resilient in that case and most MPPT chargers
seem not to be.

There are a bunch of different switching topologies. My guess there is a bunch of circulating magnetic energy that causes failure when the load is removed abruptly. You say your BMS disconnects the battery? Most of the time it\'s supposed to communicate with the charger and tell it to back off the current. Check to see if your MPPT is compatible with Li having a BMS disconnect, or that the Li is compatible with an MPPT. Send an email query to the MPPT manufacturer customer support.

In medieval Europe they would have dunked the design engineer into a
moat several times for \"moral cleansing\"
--
Regards, Joerg

http://www.analogconsultants.com/

 

[Joerg]

On 1/30/23 12:09 PM, Fred Bloggs wrote:

On Monday, January 30, 2023 at 2:48:21 PM UTC-5, Joerg wrote:
On 1/30/23 10:55 AM, Fred Bloggs wrote:
On Monday, January 30, 2023 at 1:40:50 PM UTC-5, Joerg wrote:
Attention, this is one of those rare electronics-related questions

Will be rigging up a small power-failure backup system. Essentially a
12V LiFePO4 battery (with BMS in there), inverter, solar panels, MPPT
charger.

When reading up on stuff and talking to people I found something very
disconcerting. It seems that MPPT charge controllers can and often do
commit suicide when operated without a battery. It even says that in the
manuals a lot. The trigger event can be as simple as the BMS opening for
some reason and ... *PHUT* ... MPPT is gone. A friend had that happen,
twice.

They can also send out a substantial voltage spike or short their
MOSFETs during such events, the latter letting full solar panel voltage
onto the 12V power bus. Both of which can kill rather expensive gear
connected to the 12V bus.

Why is that? Are the engineers designing this stuff not very bright? I\'d
never release a design with such \"traits\".

Does anyone know lower-end MPPT charge controllers (20-40A range) that
are properly designed in this respect? Preferably ones that are also low
noise so they don\'t mess with measurements on the lab bench. The Genasun
brand is low noise but AFAICT they only come for very low solar panel
voltages.

Of course, one solution is to build a massive crowbar to blow a fuse and
protect the connected gear. The MPPT charger might possibly still die.

I\'ve seen that as a warning, in the user\'s manual, even for those little solar battery maintainers to keep a seldom used car battery topped off.

You have to remove power to the MPPT charge controller before you remove the battery.

Yeah I know, and that really doesn\'t make sense in such a design. Any
Li-Ion battery can literally \"remove itself\" via BMS action. Any
external stuff should be resilient in that case and most MPPT chargers
seem not to be.

There are a bunch of different switching topologies. My guess there is a bunch of circulating magnetic energy that causes failure when the load is removed abruptly.

That would be a serious case of engineering blunder. I\'ve designed stuff
like this and know how it\'s done correctly. I just need to know which
MPPT mfg also knows this, since I don\'t want to roll my own again.


You say your BMS disconnects the battery? Most of the time it\'s supposed
to communicate with the charger and tell it to back off the current.


That is not realistic when you are using an off-the-shelf Li-Ion
battery, as is customary. They generally do not have any communications
interfaces. And with a properly designed MPPT it isn\'t necessary.

Very occasionally a large Li-Ion battery will have Bluetooth
connectivity but that\'s mainly for relaying the charge status.


Check to see if your MPPT is compatible with Li having a BMS disconnect,
or that the Li is compatible with an MPPT. Send an email query to the
MPPT manufacturer customer support.


Everytime I asked the answer was no :-(

[...]

--
Regards, Joerg

http://www.analogconsultants.com/

 

[boB]

On Mon, 30 Jan 2023 12:35:43 -0800, Joerg <news@analogconsultants.com>
wrote:

On 1/30/23 12:09 PM, Fred Bloggs wrote:
On Monday, January 30, 2023 at 2:48:21 PM UTC-5, Joerg wrote:
On 1/30/23 10:55 AM, Fred Bloggs wrote:
On Monday, January 30, 2023 at 1:40:50 PM UTC-5, Joerg wrote:
Attention, this is one of those rare electronics-related questions

Will be rigging up a small power-failure backup system. Essentially a
12V LiFePO4 battery (with BMS in there), inverter, solar panels, MPPT
charger.

When reading up on stuff and talking to people I found something very
disconcerting. It seems that MPPT charge controllers can and often do
commit suicide when operated without a battery. It even says that in the
manuals a lot. The trigger event can be as simple as the BMS opening for
some reason and ... *PHUT* ... MPPT is gone. A friend had that happen,
twice.

They can also send out a substantial voltage spike or short their
MOSFETs during such events, the latter letting full solar panel voltage
onto the 12V power bus. Both of which can kill rather expensive gear
connected to the 12V bus.

Why is that? Are the engineers designing this stuff not very bright? I\'d
never release a design with such \"traits\".

Does anyone know lower-end MPPT charge controllers (20-40A range) that
are properly designed in this respect? Preferably ones that are also low
noise so they don\'t mess with measurements on the lab bench. The Genasun
brand is low noise but AFAICT they only come for very low solar panel
voltages.

Of course, one solution is to build a massive crowbar to blow a fuse and
protect the connected gear. The MPPT charger might possibly still die.

I\'ve seen that as a warning, in the user\'s manual, even for those little solar battery maintainers to keep a seldom used car battery topped off.

You have to remove power to the MPPT charge controller before you remove the battery.

Yeah I know, and that really doesn\'t make sense in such a design. Any
Li-Ion battery can literally \"remove itself\" via BMS action. Any
external stuff should be resilient in that case and most MPPT chargers
seem not to be.

There are a bunch of different switching topologies. My guess there is a bunch of circulating magnetic energy that causes failure when the load is removed abruptly.


That would be a serious case of engineering blunder. I\'ve designed stuff
like this and know how it\'s done correctly. I just need to know which
MPPT mfg also knows this, since I don\'t want to roll my own again.


You say your BMS disconnects the battery? Most of the time it\'s supposed
to communicate with the charger and tell it to back off the current.


That is not realistic when you are using an off-the-shelf Li-Ion
battery, as is customary. They generally do not have any communications
interfaces. And with a properly designed MPPT it isn\'t necessary.

Very occasionally a large Li-Ion battery will have Bluetooth
connectivity but that\'s mainly for relaying the charge status.


Check to see if your MPPT is compatible with Li having a BMS disconnect,
or that the Li is compatible with an MPPT. Send an email query to the
MPPT manufacturer customer support.


Everytime I asked the answer was no :-(

[...]

I have dealt with this directly. The problem is that when the MPPT
is charging hard and that load is abruptly disconnected, it is like a
tug of war with a rope where if one person lets go, the person at the
other end may fall down. In this case, the PWM is such that if the
current suddenly goes to zero, the input voltage of a synchronous buck
converter can go sky-high and breal the FETs.

In my old designs, I tested for this same thing except with lead acid
batteries and the circuit breaker to the battery from the MPPT
controller.

Communications from the BMS to MPPT, if it is even there, is most
likely not fast enough to stop this but might be in some cases.

Was this a Chinese product ?

boB

 

[Lasse Langwadt Christensen]

mandag den 30. januar 2023 kl. 23.07.46 UTC+1 skrev boB:

On Mon, 30 Jan 2023 12:35:43 -0800, Joerg <ne...@analogconsultants.com
wrote:
On 1/30/23 12:09 PM, Fred Bloggs wrote:
On Monday, January 30, 2023 at 2:48:21 PM UTC-5, Joerg wrote:
On 1/30/23 10:55 AM, Fred Bloggs wrote:
On Monday, January 30, 2023 at 1:40:50 PM UTC-5, Joerg wrote:
Attention, this is one of those rare electronics-related questions

Will be rigging up a small power-failure backup system. Essentially a
12V LiFePO4 battery (with BMS in there), inverter, solar panels, MPPT
charger.

When reading up on stuff and talking to people I found something very
disconcerting. It seems that MPPT charge controllers can and often do
commit suicide when operated without a battery. It even says that in the
manuals a lot. The trigger event can be as simple as the BMS opening for
some reason and ... *PHUT* ... MPPT is gone. A friend had that happen,
twice.

They can also send out a substantial voltage spike or short their
MOSFETs during such events, the latter letting full solar panel voltage
onto the 12V power bus. Both of which can kill rather expensive gear
connected to the 12V bus.

Why is that? Are the engineers designing this stuff not very bright? I\'d
never release a design with such \"traits\".

Does anyone know lower-end MPPT charge controllers (20-40A range) that
are properly designed in this respect? Preferably ones that are also low
noise so they don\'t mess with measurements on the lab bench. The Genasun
brand is low noise but AFAICT they only come for very low solar panel
voltages.

Of course, one solution is to build a massive crowbar to blow a fuse and
protect the connected gear. The MPPT charger might possibly still die.

I\'ve seen that as a warning, in the user\'s manual, even for those little solar battery maintainers to keep a seldom used car battery topped off.

You have to remove power to the MPPT charge controller before you remove the battery.

Yeah I know, and that really doesn\'t make sense in such a design. Any
Li-Ion battery can literally \"remove itself\" via BMS action. Any
external stuff should be resilient in that case and most MPPT chargers
seem not to be.

There are a bunch of different switching topologies. My guess there is a bunch of circulating magnetic energy that causes failure when the load is removed abruptly.


That would be a serious case of engineering blunder. I\'ve designed stuff
like this and know how it\'s done correctly. I just need to know which
MPPT mfg also knows this, since I don\'t want to roll my own again.


You say your BMS disconnects the battery? Most of the time it\'s supposed
to communicate with the charger and tell it to back off the current.


That is not realistic when you are using an off-the-shelf Li-Ion
battery, as is customary. They generally do not have any communications
interfaces. And with a properly designed MPPT it isn\'t necessary.

Very occasionally a large Li-Ion battery will have Bluetooth
connectivity but that\'s mainly for relaying the charge status.


Check to see if your MPPT is compatible with Li having a BMS disconnect,
or that the Li is compatible with an MPPT. Send an email query to the
MPPT manufacturer customer support.


Everytime I asked the answer was no :-(

[...]
I have dealt with this directly. The problem is that when the MPPT
is charging hard and that load is abruptly disconnected, it is like a
tug of war with a rope where if one person lets go, the person at the
other end may fall down. In this case, the PWM is such that if the
current suddenly goes to zero, the input voltage of a synchronous buck
converter can go sky-high and breal the FETs.

a sync buck can pump energy from the output to the input but if there is
no longer a battery on output, where does the energy come from?

there is of course some energy in the inductor but is that really enough
to rise the voltage with reasonable output and input caps?

 

[Joerg]

On 1/30/23 2:07 PM, boB wrote:

On Mon, 30 Jan 2023 12:35:43 -0800, Joerg <news@analogconsultants.com
wrote:

On 1/30/23 12:09 PM, Fred Bloggs wrote:
On Monday, January 30, 2023 at 2:48:21 PM UTC-5, Joerg wrote:
On 1/30/23 10:55 AM, Fred Bloggs wrote:
On Monday, January 30, 2023 at 1:40:50 PM UTC-5, Joerg wrote:
Attention, this is one of those rare electronics-related questions

Will be rigging up a small power-failure backup system. Essentially a
12V LiFePO4 battery (with BMS in there), inverter, solar panels, MPPT
charger.

When reading up on stuff and talking to people I found something very
disconcerting. It seems that MPPT charge controllers can and often do
commit suicide when operated without a battery. It even says that in the
manuals a lot. The trigger event can be as simple as the BMS opening for
some reason and ... *PHUT* ... MPPT is gone. A friend had that happen,
twice.

They can also send out a substantial voltage spike or short their
MOSFETs during such events, the latter letting full solar panel voltage
onto the 12V power bus. Both of which can kill rather expensive gear
connected to the 12V bus.

Why is that? Are the engineers designing this stuff not very bright? I\'d
never release a design with such \"traits\".

Does anyone know lower-end MPPT charge controllers (20-40A range) that
are properly designed in this respect? Preferably ones that are also low
noise so they don\'t mess with measurements on the lab bench. The Genasun
brand is low noise but AFAICT they only come for very low solar panel
voltages.

Of course, one solution is to build a massive crowbar to blow a fuse and
protect the connected gear. The MPPT charger might possibly still die.

I\'ve seen that as a warning, in the user\'s manual, even for those little solar battery maintainers to keep a seldom used car battery topped off.

You have to remove power to the MPPT charge controller before you remove the battery.

Yeah I know, and that really doesn\'t make sense in such a design. Any
Li-Ion battery can literally \"remove itself\" via BMS action. Any
external stuff should be resilient in that case and most MPPT chargers
seem not to be.

There are a bunch of different switching topologies. My guess there is a bunch of circulating magnetic energy that causes failure when the load is removed abruptly.


That would be a serious case of engineering blunder. I\'ve designed stuff
like this and know how it\'s done correctly. I just need to know which
MPPT mfg also knows this, since I don\'t want to roll my own again.


You say your BMS disconnects the battery? Most of the time it\'s supposed
to communicate with the charger and tell it to back off the current.


That is not realistic when you are using an off-the-shelf Li-Ion
battery, as is customary. They generally do not have any communications
interfaces. And with a properly designed MPPT it isn\'t necessary.

Very occasionally a large Li-Ion battery will have Bluetooth
connectivity but that\'s mainly for relaying the charge status.


Check to see if your MPPT is compatible with Li having a BMS disconnect,
or that the Li is compatible with an MPPT. Send an email query to the
MPPT manufacturer customer support.


Everytime I asked the answer was no :-(

[...]

I have dealt with this directly. The problem is that when the MPPT
is charging hard and that load is abruptly disconnected, it is like a
tug of war with a rope where if one person lets go, the person at the
other end may fall down. In this case, the PWM is such that if the
current suddenly goes to zero, the input voltage of a synchronous buck
converter can go sky-high and breal the FETs.

There is supposed to be at least some capacitance on the output that
would prevent this. So far all the converters I designed react
immediately and do not let the output overshoot even with a suddenly
disconnected load. It can be done within one cycle so you don\'t need
much in terms of capacitance. One of them was an MPPT design. That one
you could even use as a stand alone power supply, sans battery, provided
the panels delivered enough juice.

It\'s the same in other situations. I designed an actuator circuit where
then the client encountered the unforseen situation where the load would
accidentally come off. It\'s taken care of by a FET that immediately
takes over and bleeds off the energy in the inductor for that one cycle.
IOW it briefly goes linear. If something shoots up sky-high that is a
design flaw in my opinion.

In my old designs, I tested for this same thing except with lead acid
batteries and the circuit breaker to the battery from the MPPT
controller.

I\'d even test with lead acid because there could always be a gradual
corrosion or loosening at one of the contacts. I once sat there in a
borrowed old Chevy truck. Wouldn\'t start after loading my stuff and
others around me became impatient. Popped the hood, wiggled some cables
and the positive terminal on the battery came right off.

Communications from the BMS to MPPT, if it is even there, is most
likely not fast enough to stop this but might be in some cases.

True. Plus it shall not be relied upon anyhow. Comms can fail quietly,
then the alert doesn\'t come and ... whaddabam.

Was this a Chinese product ?

I was told it was Californian. I\'ll probably receive one of the failed
units some time in February to have a look.

Anyhow, I\'ll include a big fat crowbar on this system because I don\'t
trust design engineers in that industry much anymore. There\'s too much
money connected to the 12V bus.

--
Regards, Joerg

http://www.analogconsultants.com/