Batteries not charging even though solar voltage good

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David Cashin

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Jul 24, 2021, 3:39:57 PMJul 24
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We've had an 8 cell lifepo4 setup at the cabin running smoothly for a few months. It charged the batteries when we are away.

Upon returning to the cabin we noticed the incoming solar amperage on the monitoring page was showing 0.000A and the SOC was 30%, it's usually 100%.

We confirmed the incoming solar is about 37v.

We have a disconnect between the DSSR output and the PV shunt (I'll call this the solar breaker). With the solar breaker disconnected the DSSR light blinks red. When we switch extio 4 from 1 to 0 it stops blinking. We take this to mean there is communication from the SBMS to the DSSR via the DEXT.

Any ideas why the incoming pv is not charging the batteries?

Thank you

Dacian Todea

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Jul 24, 2021, 8:25:04 PMJul 24
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David,

A photo of the screen of the SBMS0 will have been useful.
But it also sounds like the DEXT and DSSR20 LED's are red meaning charging is enabled so maybe something got damaged like maybe the breaker between the DSSR20 and shunt may be damaged.
The blinking part is strange almost like there is a short circuit on the DSSR20 output. Any chance water got inside the DSSR20 ?


David Cashin

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Jul 26, 2021, 8:13:32 AMJul 26
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I confirmed the breaker and shunt are still working (the shunt resistance slightly increases when current is passed through it).

When I disconnected the solar breaker and measured the voltage coming from the DSSR, it was 13-15V, I assume it's supposed to be ~26V?

No signs of water damage - also no visible markings on the circuitry on the back of the DSSR.

Attached are some photos of the system. I tried a factory reset and re-saving the battery parameters, which is why the SOC reads 49%.

Usually when we leave, we disconnect the breaker to the inverter for safety, but leave the solar breaker on so that the batteries can charge and balance. Last week, we accidentally did the opposite - disconnected incoming solar power (breaker located between the DSSR and PV Shunt), and left the inverter breaker on, although the inverter itself was turned off. When we came back a week later, the battery SOC was about 40%. I'm trying to understand how/if the two are related, not sure a turned off inverter and the SBMS could drain 60% of our 270Ah battery bank in one week. I'm wondering if this somehow might have damaged the DSSR.
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Dacian Todea

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Jul 26, 2021, 2:50:00 PMJul 26
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You should not have done a factory reset as that will not help with anything. Factory reset will not reset anything related to Parameter settings it will only reset to default all settings in Device settings and Automation so EXT IOx and shunt values will be reset.
Also there is nothing wrong with the SBMS0 nor with the DEXT16 the problem is strictly your solar panel or the DSSR20
I see the DEXT16 red LED meaning that SBMS0 requests charging and DEXT16 has red LED ON meaning it is OK but the signal either is not getting to DSSR20 so check that remote wire from RCBatt to Batt and if that is OK then check your solar panel maybe some fuse or breaker if there is one between the panel/panels and DSSR20
I know you mentioned 37V from solar still there may not be any current and just a leakage to a damaged breaker or fuse if you have any.
Measure the RCBatt voltage but I assume that will be OK
I can not see in the photo if the DSSR20 LED is either green, red or just OFF.  Eventually uninstall the DSSR20 and take a photo on the back of the DSSR20 (where the components are).

 

David Cashin

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Jul 26, 2021, 3:11:16 PMJul 26
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After the factory reset I put EXT and shunt values back to what they should be.

The solar panels are providing 37V directly to the DSSR (no fuse on that wire, the breaker is between PV shunt and DSSR), and when we bypass the solar breaker with a wire there is still no charging indication on the SBMS. I assume we can just attach an ammeter to the solar panels to confirm they have current?

The DSSR light is off, except it blinks when we disconnect the DSSR pos output wire. Attached is a photo of the back of circuit board from the weekend. Best my camera can do, if there's anything specific I should check I can do that on the next trip. I looked for any black marks or stains, did not see any. 

When I return I will check the RCBatt-Batt remote wire, but FYI when we disconnected the solar breaker, and switch extio 4 from 1 to 0 the DSSR stops blinking. I take this to mean there is communication from the SBMS to the DSSR via the DEXT.


IMG_20210725_125911 (1).jpg

David Cashin

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Jul 26, 2021, 4:08:24 PMJul 26
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Here's another angle of the system, as well as a photo of the SBMS from a few weeks ago when things were running a-ok.

If it helps, I can draw up a clearer diagram of how we have things wired up.
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Dacian Todea

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Jul 27, 2021, 3:46:27 PMJul 27
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In the old photo I see the green LED light ON so not charging just diversion. Do you get the green LED ON the DSSR20 now when charging is disabled like maybe having the EXT IO4 set as type 0 ?
The LED I assume is blinking red when battery positive is disconnected from the DSSR20 ?
In the SBMS0 photo I see a small charge current while charging is disabled not sure why that is ? Maybe you did not had the EXT IO3 and IO4 properly connected before powering the SBMS0
When breaker connected to battery+ is disconnected the red LED should be solid red and not blinking so something is wrong. It will blink if there was a short circuit on the output so between Battery+ and Battery- terminal  so maybe a short circuited ceramic capacitor. 
There are a total of 3x 100V 1uF capacitors the taller larger ones two of them close to the 8pin Linear technology IC and the other one close to the tall 4 pin optoisolator looking device.  If one of this has a short circuit then that can be an explanation but not sure how or why will this 100V rated capacitors be damaged.


David Cashin

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Jul 27, 2021, 10:12:42 PMJul 27
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Right, that photo was taken when the system was up and fully charged - once SOC reached 100 it switched to green. Right now, the light is off, and I believe off when IO4 set to 0 as well.

Yes, LED blinks red when DSSR20 pos is disconnected.

Good to know that blinking indicates short circuit. I will investigate that further. I will test the caps to make sure they are ok - I will use the method described here: https://www.ifixit.com/Wiki/Troubleshhoting_logic_board_components
(resistance reading across cap leads should slowly move towards infinity - if it stays at zero then it seems the cap is bad, according to this article)

Will also confirm the PV current and the RCBatt-Batt remote wire.

Still puzzling over why the DSSR output was 13-15V with pos wire disconnected, I assume it should be 27ish volts?

Dacian Todea

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Jul 28, 2021, 12:46:30 PMJul 28
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David,

It will be very strange for the LED on both DEXT16 and DSSR20 not to be green as the green part is completely separate path.
The output of DSSR20 will have been the same as input from PV panels if all worked correctly and the red LED was ON. Whit intermittent/blinking red LED then you will get some sort of half or less than half if the short circuit protection turns that OFF for most of the time. The output will be 36 or 37V or whatever PV input voltage is if the DSSR20 is not connected to battery and LED is normal solid red.
You can remove two of the 3 capacitors and test to see if the DSSR20 works correctly. If so then one of the two you removed may have a short probably mechanical damage or some sort of over-voltage at some point well above the spec 100V.

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