End Amps comparison

[SolarMusher]

Hi
I was looking for the best end amps on a rolls battery bank (48V/700Ah). This is a Magnum system with BMK and Whizbang installed on the same shunt. At the end of Absorb, RTR BMK was showing DC amps with very small change (0.2amps) when the Whizbang was showing larger change (0.2 to 1.5amps) which make it difficult to end accurately the charge.
Example: it was easy to set the RTR BMK to end at 10amps because it was displaying a steady 9 to 9.2amps without larger variations. The whizbang was more difficult to set because amps were changing continuously from 8.6 to 10.5 in less than a minute so had to set it higher to 11amps where I'd be sure the Classic could stop and not overcharge. I know that we are talking about peanuts but why these larger variations on the whizbang when they are on the same shunt ?
Thanks,
Erik

[Westbranch]

Erik, did you have a time period set as well for EA to be met?

[vtmaps]

I know that we are talking about peanuts but why these larger variations on the whizbang when they are on the same shunt ?

The variations are caused by the timing of the sampling and averaging.  It's been discussed in another thread and the Midnite folks will improve it in a future upgrade.

Meanwhile, as Westbranch alluded to, you can set the end amps to be triggered after a certain time (like a minute).  That means the small variations will not matter.

--vtMaps

[SolarMusher]

HI,
What time are you talking about? Did you talk about absorb time? if so yes, 2hr30 for 700Ah.
Is there anything else where I could modify this delay (1 minute) to trigger end absorb after EA value from the shunt has been met?
I didn't see anything 
Thanks,
Erik

[SolarMusher]

vt,
I've read that post. Will wait for boB to chime a more accurate output for the Whizbang. As Vic did it, I had also increased EA a bit (1amps) to be sure.
Thanks,
Erik

[boB]

I would say to watch the WB Jr. amps over a "few" hours of Absorb charging and
plot the amps into the battery (as best you can) over that time.  Ignore times
where the battery voltage is below the absorb voltage (i.e. when it is in Bulk MPPT)

When that current tapers off and no longer goes any lower, that is the lowest it
can be of course.  You couldn't set the EA to anything below that line so EA would
want to be set to somewhere above that current.  The question is how much higher ?
Until we get the WB Jr. current averaged or slowed down a bit more, it will have to
be something higher than that lowest current.

I'd love to see one of your plots if you decide to do this.

boB

[SolarMusher]

Allo boB,
I would like to plot it but how is another question  .
There's no internet there and loc app is not an option.
Is there a way to connect a Classic directly to my laptop now without internet/router?
Any thoughts? I'm afraid that you're thinking of me and my pen, I'll never be fast enough  .

The question is how much higher ?
Until we get the WB Jr. current averaged or slowed down a bit more, it will have to
be something higher than that lowest current.
I'd love to see one of your plots if you decide to do this.
boB

I would say 1.5 to 2 amps higher.
Erik

[boB]

Allo boB,
I would like to plot it but how is another question  .
There's no internet there and loc app is not an option.
Is there a way to connect a Classic directly to my laptop now without internet/router?
Any thoughts? I'm afraid that you're thinking of me and my pen, I'll never be fast enough  .

The question is how much higher ?
Until we get the WB Jr. current averaged or slowed down a bit more, it will have to
be something higher than that lowest current.
I'd love to see one of your plots if you decide to do this.
boB

I would say 1.5 to 2 amps higher.
Erik

Yes, you and your pen.   Just write down a current value once every 5 minutes or so.  Actually, the 5 minute
logging should do the trick as it logs the values every 5 minutes.  Then you just look at the graph and/or
take a picture of it with your digital camera or phone.

This is easier if you make sure unnecessary loads are off and the sun it shining so it can stay
in absorb as long of a stretch as possible so you have one good long data capture time.
boB

[vtmaps]

When that current tapers off and no longer goes any lower, that is the lowest it
can be of course.

Yes.  Assuming that Vabs is high enough, or that you have an electrolyte recirculation system. 

If Vabs is too low (or for too short a time) to thoroughly stir the electrolyte in a flooded battery, the electrolyte will be stratified and you can asymptotically approach an 'end amps' that does not represent fully charged.

An example of when this may occur:
Discharge causes stratification and a battery at 90% SOC can be stratified.  As the sun comes up the battery slowly approaches Vabs, but by the time it gets to gassing voltage the battery is almost fully charged, but still stratified (actually more stratified because charging causes stratification).  If the charging protocol cuts off the absorb too soon (e.g. basing absorb time on bulk time) the battery may be stratified when it goes to float.  This could also happen if 'end amps' is set too high and terminates absorb before stirring is complete.

I think the use of 'end amps' can assure a full charge IF the Vabs is high enough and 'end amps' is low enough.  But how high and how low?  That is an enduring mystery to me.

It is interesting to note that many industrial battery chargers (e.g. forklift chargers) use a charging protocol with different bulk and absorb voltages.  Some protocols finish the charging with a higher than Vabs voltage for a short time.  One way or another, these protocols are designed to get the electrolyte stirred.

--vtMaps

[SolarMusher]

boB,
I will do it... as soon as we'll have a sunny day. Unfortunately, forecast are snowy everyday for the rest of the week, maybe saturday.

It is interesting to note that many industrial battery chargers (e.g. forklift chargers) use a charging protocol with different bulk and absorb voltages.  Some protocols finish the charging with a higher than Vabs voltage for a short time.  One way or another, these protocols are designed to get the electrolyte stirred.

--vtMaps

Vt,
Funny, that you're talking about this way of charge. I remember Chris Olson asking if there was a possibility for Midnite to add this charging protocol to the Classic. I would be interested to test it on my scrappy batteries.
Erik

[zoneblue]

Yes i get that too. Here with long overcast but otherwise bright mornings, at times,  bulk will be dragged out, and when it hits the absorb setpoint, drops more or less straight into float. Based on a highish EA setting (to allow for about 10A of load)

I guess the AGMs dont suffer as much from stratification, so that isnt so much an issue. My main concern is generally to not over charge them and yet also ensure that they are charged. Long pm floats always bring the WB battery amps to virtually zero. But i also have a low float set point, currently 26.64V.

When the local app allows us to set EA termination to WBJr, that will be better.

[SolarMusher]

I charged the bank yesterday evening on my system with the gen and watched end current closely on the Magnum BMK and Whizbang which is mounted on an E-panel shunt. Whizbang variations were as little as the BMK with a steady .2, .3 amps and matched the BMK until it reached 9.2amps (830Ah). In fact, it was very different from what I saw on cutomer's system in a Magnum panel where the whizbang was mounted inside a Classic and wired remotely to the shunt. End current had larger changes (until 1.5amps). I'm thinking now that it's because of the remote install I did, using a 18 inches wire to connect to the shunt.
Do you think I could have it more accurate if I make this wire shorter? Another reason could be that the Whiz is mounted inside the classic wiring casing. Any thoughts about that?
Great Christmas time to all,
Erik

[boB]

18 inches is a ways away but you might try twisting the wires if you have not done that already

[zoneblue]

What about using some screened audio cable?

[boB]

What about using some screened audio cable?

Yes, maybe.  I'm not sure exactly what the problem or symptoms are here.
I would not think that noise would be an issue because everything is happening
at a real low frequency, but who knows ?

If shielded audio cable used, would it be 2 center conductors plus a shield ?
I would say if it is, to only ground the shield at one end.  Maybe at the shunt end ?

boB