Wondering about the midnite solar BCM....

[qrper]

Got off of my duff and got around to hooking the BCM up. Now I know it's not a Fluke 77, not even close, but I wondering why the BCM shows 80% SOC when the whizbang jr reports 98% capacity

How long doe it take for the BCM to turn off the bottom red LED? It's been four or five days and it reports that the battery bank hasn't been fully charged, yet I'm in float condition all those days.

Just wondering..

mike

[boB]

I think this is because the BCM does not know that you have replaced any amp-hours removed from the battery.

The WB Jr. knows this and so has an idea of re-charge.  The WB Jr. and Classic also knows when you have finished an Absorb charge cycle which is a timed amount of battery voltage at or above that Absorb voltage.  The Classic and WB Jr. uses that information to reset your SOC to 100% because it almost always means your battery has had plenty of returned-amps.  It's hard to any meaningful amount of Absorb time without returning the amp-hours that was removed PLUS the inefficiency of a few percent so that is a great time to reset SOC and sanity check the numbers.

The BCM only knows battery voltage.   So, as long as the battery voltage is above a decent Absorb voltage set-point for at least 2 hours, the BCM will call it charged.  100% SOC.

From then on, the battery voltage by itself is s good "guess" as to the battery's SOC typically.  It's slow responding so instantaneous voltage changes should not cause an abrupt change in SOC% on the BCM.

There is an LED on the BCM that shows that it has not seen  the battery at Absorb voltage for 1 and 2 weeks.

You don't need an Absorb cycle to replenish the Amp-Hours of the battery BUT you do need to Absorb them once in a while to avoid sulfation of the battery plates.

[qrper]

I think this is because the BCM does not know that you have replaced any amp-hours removed from the battery.

The WB Jr. knows this and so has an idea of re-charge.  The WB Jr. and Classic also knows when you have finished an Absorb charge cycle which is a timed amount of battery voltage at or above that Absorb voltage.  The Classic and WB Jr. uses that information to reset your SOC to 100% because it almost always means your battery has had plenty of returned-amps.  It's hard to any meaningful amount of Absorb time without returning the amp-hours that was removed PLUS the inefficiency of a few percent so that is a great time to reset SOC and sanity check the numbers.

The BCM only knows battery voltage.   So, as long as the battery voltage is above a decent Absorb voltage set-point for at least 2 hours, the BCM will call it charged.  100% SOC.

From then on, the battery voltage by itself is s good "guess" as to the battery's SOC typically.  It's slow responding so instantaneous voltage changes should not cause an abrupt change in SOC% on the BCM.

There is an LED on the BCM that shows that it has not seen  the battery at Absorb voltage for 1 and 2 weeks.

You don't need an Absorb cycle to replenish the Amp-Hours of the battery BUT you do need to Absorb them once in a while to avoid sulfation of the battery plates.

Bob... everything is working fine... The batteries are going into absorb each day and they end up in float condition.
I was wondering why the BCM is not showing the green everything is fine LED instead of the red oh crap LED.

I've had the BCM connected to the batteries now for about a week and while the moving display shows 100%, the red LED is still telling me the battery hasn't been charged in two weeks. Of course, that's simply not true.

A piece of black tape would certainly solve the problem.

mike

[boB]

Bob... everything is working fine... The batteries are going into absorb each day and they end up in float condition.
I was wondering why the BCM is not showing the green everything is fine LED instead of the red oh crap LED.

I've had the BCM connected to the batteries now for about a week and while the moving display shows 100%, the red LED is still telling me the battery hasn't been charged in two weeks. Of course, that's simply not true.

A piece of black tape would certainly solve the problem.

mike

How long is it Absorbing ? 

And at what voltage ?

If not long enough and if not above the threshold voltage, the BCM won't think it's charged.


What is the BCM set for ?   Isn't there a jumper to pick between two battery types ? (I can't remember)

[qrper]

Bob... everything is working fine... The batteries are going into absorb each day and they end up in float condition.
I was wondering why the BCM is not showing the green everything is fine LED instead of the red oh crap LED.

I've had the BCM connected to the batteries now for about a week and while the moving display shows 100%, the red LED is still telling me the battery hasn't been charged in two weeks. Of course, that's simply not true.

A piece of black tape would certainly solve the problem.

mike

How long is it Absorbing ? 

And at what voltage ?

If not long enough and if not above the threshold voltage, the BCM won't think it's charged.


What is the BCM set for ?   Isn't there a jumper to pick between two battery types ? (I can't remember)

 absorb is set for 58.8V for four hours.
The system is 48 V
I have it set for lead acid batteries which is what I'm using

[boB]

 absorb is set for 58.8V for four hours.
The system is 48 V
I have it set for lead acid batteries which is what I'm using

WoW !  Then, I wonder what is going on ?

Is it possible that there is a voltage drop while in Absorb that would make the BCM think that the battery voltage is actually lower than the charger is putting out at its terminals ?

Do you remember the voltage the BCM needs for that setting ?  Sounds like 58.8V should be good.

Remember that the BCM doesn't know what the battery temperature is if the charger is compensating that set-point voltage.

OTHERWISE, maybe the BCM is not reading the voltage correctly and you need a new one ?   If so, you could call support and tell them I sent you.

[qrper]

 absorb is set for 58.8V for four hours.
The system is 48 V
I have it set for lead acid batteries which is what I'm using

WoW !  Then, I wonder what is going on ?

Is it possible that there is a voltage drop while in Absorb that would make the BCM think that the battery voltage is actually lower than the charger is putting out at its terminals ?

Do you remember the voltage the BCM needs for that setting ?  Sounds like 58.8V should be good.

Remember that the BCM doesn't know what the battery temperature is if the charger is compensating that set-point voltage.

OTHERWISE, maybe the BCM is not reading the voltage correctly and you need a new one ?   If so, you could call support and tell them I sent you.

Bob and the group,
 
Still have the led LED on, battery is in float condition already (11AM), nice bright sunny day here.

I was thinking... If I were to connect the BCM to one of my bench power supplies, I could easily fake any voltage
 condition that the BCM might want to see

So, if I keep with a 48 V battery, what would be the voltages needed to convince the status led to do their thing? And what would the hold time for any particular set point be?

I've had this one nailed to the garage wall for a week now, and other than seeing the moving LEDs move a bit, the status LEDs remain in red

Do you think this would work, bob?

Mike

[boB]

Yep.  Connect  the BCM to your power supply and set it to as close to 60V as you can. 

THAT should do it if anything will.  Keep it there all day or all night if you need to.

If that LED does not go off, then let's just send you a new BCM.

boB

[Vic]

Have been wondering,  if you are using EA to end Absorb,  Mike.

If,  so,   this might end Absorb before the required 2 hour  minimum,  needed to satisfy the BCM.

Just a thought,   73 to all,    Vic

[qrper]

Have been wondering,  if you are using EA to end Absorb,  Mike.

If,  so,   this might end Absorb before the required 2 hour  minimum,  needed to satisfy the BCM.

Just a thought,   73 to all,    Vic

Vic,

I thought about that. So I changed the jumper inside the BCM so now instead of lead acid it's set on AGM.
So far, the red LED is still on.
Now with the longer and brighter days, the batteries are in float at 10AM, so I know that the absorb time isn't kicking in. It's set for four hours, and of course at 10 in the morning, the battery bank certainly hasn't been in absorb for the total of four hours.
I have a greenhouse full of plants and as soon as I manage to get some free time, I'm going to pull the BCM and connect it to my power supply and see if I can't fake it out.

mike

[boB]

Have you tried disconnecting the power to the BCM and reconnecting it ?

The BCM reads and interprets the nominal battery voltage when you do that.

[qrper]

Have you tried disconnecting the power to the BCM and reconnecting it ?

The BCM reads and interprets the nominal battery voltage when you do that.

I'll try that tonight so it has a fresh start in the morning

mike