Lithium smart shunt charging weirdness

[webcraft]

I have a 60ah LiFePo battery for running the trolling motor that has replaced our unreliable 2hp outboard.
When I first got the battery I brought it up to a full charge using the supplied 230v charger. I then installed the battery in a box with a breaker and a smart shunt. The battery has an anderson terminal to connect it either to the motor or to a 100W solar panel running through a Victron SmartSolar charger.

Charging the battery from the solar panel is very succesful. Today though we are in a marina and so I plugged the battery into the mains charger. (This, I should add, is via a dedicated socket that I presume is connected to the LiFePo's BMS). The SmartShunt showed no input current and over an hour did not manage to raise the soc by even one percent.

The battery is now back on the solar panel, and the shunt shows that the soc has increased by 5‰ in an hour, with 3.5A / 50W going in.

So it looks as though I can no longer charge the battery via the inbuilt mains charging port. Any ideas?

— W

 

[webcraft]

(I am wondering about just putting an Anderson connector on the 230v charger and bypassing the internal charging circuitry)

- W

 

[Refueler]

Your case is similar to one reported on a model forum.... in 'reverse order' ...

Model flyers are always looking for ways to charge their liPo's for flight on the field.

Guy bought a LiFePo4 80A/hr battery designed to replace Lead Acid - reasoning being that instead pf 30 - 40A/hr from a LA .. he could get maybe 60A/Hr from the lithium ...

He could charge the battery OK with the recc'd charger ... but when he connected the battery to his charger to charge his LiPo batts - no voltage - no amps ... nothing. When he tried charging the LiFePo4 with charger that was said to be compatible - it again refused.

He delved into the matter deeply and found that the BMS front end of the LiFePo4 was the limiting factor .. it did not like initial 'shock' load on connection .. so he added anti-spark resistors to control the load when using the LiFePo4 to power the LiPo charger ... worked as it made the initial demand lower and BMS did not interpret as a short.
To get the LiFePo4 to charge - he found that most chargers that were supposed to be good to charge had initial 'shock' that again BMS shut down .. he changed to a more controlled charger that brought up charge in stages rather than BHAM ! and the BMS was happy.

I relate this purely as an indication that some BMS are overly sensitive ... and it may not be case of OP's ... but worth considering.

 

[webcraft]

Your case is similar to one reported on a model forum.... in 'reverse order' ...

Model flyers are always looking for ways to charge their liPo's for flight on the field.

Guy bought a LiFePo4 80A/hr battery designed to replace Lead Acid - reasoning being that instead pf 30 - 40A/hr from a LA .. he could get maybe 60A/Hr from the lithium ...

He could charge the battery OK with the recc'd charger ... but when he connected the battery to his charger to charge his LiPo batts - no voltage - no amps ... nothing. When he tried charging the LiFePo4 with charger that was said to be compatible - it again refused.

He delved into the matter deeply and found that the BMS front end of the LiFePo4 was the limiting factor .. it did not like initial 'shock' load on connection .. so he added anti-spark resistors to control the load when using the LiFePo4 to power the LiPo charger ... worked as it made the initial demand lower and BMS did not interpret as a short.
To get the LiFePo4 to charge - he found that most chargers that were supposed to be good to charge had initial 'shock' that again BMS shut down .. he changed to a more controlled charger that brought up charge in stages rather than BHAM ! and the BMS was happy.

I relate this purely as an indication that some BMS are overly sensitive ... and it may not be case of OP's ... but worth considering.

That is interesting, but the mains charger (which came with the battery) did initially charge it - though I had no way then of monitoring the soc, just left it on until the light went green.

I think the BMS doesn't like the smart shunt when the mains charger is on. Now up to 86‰ soc with the solar panel.

 

[Sea Change]

Is the mains charging socket bypassing the shunt?

 

[webcraft]

Is the mains charging socket bypassing the shunt?

Probably, but the shunt should still show the soc of the battery and it didn't go up at all.

 

[B27]

Measure the battery volts?

 

[webcraft]

Measure the battery volts?

It does show the battery volts, but that is not a very accurate way of calculating the soc

 

[Sea Change]

Probably, but the shunt should still show the soc of the battery and it didn't go up at all.

The shunt just measures the current going through it, in one direction or the other. All charge and load connections have to go through it.

 

[Sea Change]

It does show the battery volts, but that is not a very accurate way of calculating the soc

Especially with LiFePO4

 

[B27]

It does show the battery volts, but that is not a very accurate way of calculating the soc

It's a very accurate way of telling if the charger is broken or not!
If the volts don't go up when you switch the charger on, the charger is not charging.
If they do go up, but your 'SOC' indication doesn't, then maybe your SOC indication is wrong.

Problem is, we don't know what the BMS looks like.
I've seen a few circuits and read a few things about alternative approaches to BMS, but who actually knows what's in your battery?
Maybe if you actually shared the make and model of battery and charger, you'd get more useful help?
Can you test the charger on another battery?

If the 'dedicated charge socket' for the mains charger bypasses the smart shunt, then it's no surprise that the smart shunt can't see charge going in and calculate a higher SOC.
All the smart shunt will see is possibly some voltage info, which as you have noted doesn't say a lot about the current going in.
The volts will suggest it's charging but don't vary much from 0.1A going in to 10A going in.

 

[webcraft]

Battery volts went up, so the charger is working. I completed charging with the solar, and soc is at 93%, but as the shunt did not calculate current in from the charger I suspect it is pretty close to 100‰

Sea Change has suggested fitting the same connector as I use for solar charging (Anderson) to the mains charger, thus bypassing the mains charging socket. Seems like a good idea.

- W