Forum Discussion
412 Replies
pianotuna wrote:
Hi jrnymn,
Since all the controllers I've seen just look at battery voltage they switch out of bulk faster than one might expect. Often I see the Blue Sky change from float to bulk when clouds pass by.
Now that IS bizarre. hmmm.- My MS MPPT 60 will hold absorption as long as you like.
Actually you can have three different likes depending on morning start voltage. - Hi jrnymn,
Since all the controllers I've seen just look at battery voltage they switch out of bulk faster than one might expect. Often I see the Blue Sky change from float to bulk when clouds pass by. BFL13 wrote:
Could be just confusion over recharge amount vs time.
MPPT may be on for most of the recharge by looking at 50-95% vs 95-100% but it may be only on for a shorter part of the whole day, leaving much of the day with the controller "in PWM" doing Float where you can get all that "free" extra solar load running done.
Yes, exactly. I'm not looking at what time of day the bank is at full, just how much of the charge time is at the (allegedly) higher mppt rate.
But that is a good point... the sooner the better, so one can run loads without interfering with charging.- I bet there's a big difference in temperature between front and back. How hot do you think the surface of a black car gets in the summer. I bet you can get a pretty good burn.
JiminDenver wrote:
A thermometer lived on the back of a panel for over a year starting with below freezing test and running through out the summer. I never saw those panel temps and it gets plenty hot here. That's why I asked what conditions you were in to see it. - Could be just confusion over recharge amount vs time.
MPPT may be on for most of the recharge by looking at 50-95% vs 95-100% but it may be only on for a shorter part of the whole day, leaving much of the day with the controller "in PWM" doing Float where you can get all that "free" extra solar load running done. - What I'm saying is there isn't a huge difference in the amps available in MPPT vs those in PWM on my set up, if the battery could take more, it would.
- Thanks BFL, yes, that is exactly what I'm getting at.
But when someone says mppt ONLY works during bulk, it seems to imply that mppt is only working during a small portion of the charge, (or maybe half, or whatever), when in fact, it is likely operational throughout a huge portion of the charge.
For example, on a 50-100% charge, mppt could very well be in operation for as much as 90+% of the time. This could be significant, if the array is small in relation to the bank; which I imagine is usually the case. jrnymn7 wrote:
lol, yes, but I'm saying, unless the bank is very near full, mppt should REMAIN in bulk/mppt mode throughout nearly the entire charge. I don't see why a large load is needed to get it back into bulk, during a 50-9? % soc charge. With solar being at such a low amperage/C-rate, Vbatt should remain low enough to not initiate abs/constant voltage mode. Yes, once the bank is very near full, and now in cv, or already in float, then I can see a switch from cv back to cc when a significant load is applied.
I don't imagine many folks have a solar array large enough to put out more than a C/10 charge rate. (i.e; 700w solar for a 400Ah bank).
Yes the low charging rate means you get to Vabs at a high SOC in the 90s before amps taper. But what would they taper to? The acceptance rate is very low per battery by then.
I use 5 amps per 110AH as 90% SOC at 14.5v Say it is 2a per at 97% at 14.8 whatever it really is So that would be 8 amps with four batts.
So by the time you drop out of MPPT the acceptance rate could already be tapering the amps and the taper down would be at a deep slope with so little SOC to go.
Same whether MPPT or PWM for that. With the low battery acceptance rate, if this happens with the array capable of doing more, you get your "free" load running so you get a jump in amps when turning on a load. Not from some MPPT vs PWM thing but from in increase in the voltage difference with the load on.
