Community Forums

hclarkx · 01-23-2021, 01:55 PM

Is your converter or solar controller on and powered when you see 13V? If so, it seems one is holding 13V in float mode (at least until the sun is fully down or you discharge the battery some). That's fine, but does not mean the battery is fully charged. A battery will charge at 13V, and can get to full charge at 13V, but it will take 10's of hours for even a modest charge. Under normal circumstances, the battery must see 14.4 volts at the end of a bulk stage and sit through declining current over a full 14.4V absorb stage to be fully charged. At that point it can be floated at 13V though around 13.6 is more common.

The idea that the waning solar is dropping current below the usual one to two amp tail current end-of-absorb detection setting could be spot on. Very possible and plausible. The current surely will get down there at some point as the sun declines, and may very well not have completed the absorb stage.
As well, a cloud that comes over and drops the current to a very low level sure could trigger end-of-absorb. I could see that causing the converter to switch to float half way through an absorb stage. You might be onto something there. You mentioned a fairly sudden drop in current from 20 amps or 10 amps to little or no current. That could result from a dark cloud coming over quickly. If this puts the solar controller in float mode, it will stay in float mode. If you see absorb current drop this way while on the generator, then it's more likely a timer is the problem. Or both!

Do you have any details on the converter and solar controller? My solar controllers have a default absorb time-out of 2 hours. I don't think my converter has a time-out but I have no details on it (it's a WFCO).

The BMV-712 has good recording capability. How about setting that up to monitor voltage and current through a full day. I have no first-hand experience with it, but I understand it can do this. Looking at these traces, primarily the current trace, should be very telling about how the charge is occurring and how much charge you are getting (how close to 14.4V you got). The voltage trace will tell you when you switched modes in the charger.

BTW, it takes considerably more current (in ampere hours) to recharge a lead acid battery than it does to discharge it. If the loads that you power with the battery take high current, this effect is greatly increased. In an extreme case, it can take 35% more ampere hours to re-chage than it took to discharge. More typical is 10-20%. You'll see discussion of the Peukert exponent in the BMV-712 manual. It's associated with an equation that approximates this effect.

I think you are getting close!

hclarkx · 01-23-2021, 03:00 PM

I should have also mentioned that if a battery is up between about 70 an 80% SOC when the charge is started, the bulk stage will be short. The bulk stage is designed to take the battery only into this range because the battery can take a faster charge below this range. In the range above 70-80% absorb is used because the charge must be slowed to prevent overheating and electrolyte boiling and such. As the charge nears 100% late in the absorb stage, the charge rate gets very slow even though voltage is still 14.4V. This is a convenient result of battery chemistry.

H

Bobby F · 01-24-2021, 01:03 PM

Success! (I think.)

I turned off the line from my panels yesterday and today and then started my generator. I watched the meter as the amp-hour deficit number decreased steadily. Both days, instead of the meter making an abrupt jump from some number larger than -15.0aH down to zero, the meter steadily walked down by 0.1aH steps to zero. So I think the cloud-sun-cloud-sun variances that the solar charge controller were throwing at the meter were indeed triggering it to resynch too early.

I ran the genny in the mornings, and when I hit the meter's SOC mark of 100%, (with a 0.00 aH deficit reading) I turned it off and turned the solar back on and let that work on the remaining top-off charging.

Both days, I have ended up with a very acceptable ending voltage on the batteries - right at 12.98v.

I'm a happy, charged-up camper again. Thanks for the help!

hclarkx · 01-25-2021, 12:49 AM

Quote:

Originally Posted by Bobby F

Success! (I think.)

I turned off the line from my panels yesterday and today and then started my generator. I watched the meter as the amp-hour deficit number decreased steadily. Both days, instead of the meter making an abrupt jump from some number larger than -15.0aH down to zero, the meter steadily walked down by 0.1aH steps to zero. So I think the cloud-sun-cloud-sun variances that the solar charge controller were throwing at the meter were indeed triggering it to resynch too early.

I ran the genny in the mornings, and when I hit the meter's SOC mark of 100%, (with a 0.00 aH deficit reading) I turned it off and turned the solar back on and let that work on the remaining top-off charging.

Both days, I have ended up with a very acceptable ending voltage on the batteries - right at 12.98v.

I'm a happy, charged-up camper again. Thanks for the help!

Cool. Though you might want to have the solar on at daybreak and run the generator along with it. This way the you will get through bulk state a bit quicker and there will be no question of the solar continuing through it's stages. If the solar is turned on later and sees a higher voltage left by the generator, it may go directly into float. The solar controller may need to see a voltage under 12.6V to go into bulk mode and that may only be available early before you start the generator. From what you said, this didn't seem to happen, but will with most solar controllers.

Also, if you expect a reasonably sunny day, turn the morning generator run off at 75-80% SOC and let the solar finish the job. The reason is that at this point the converter powered by the generator is going to go into absorb mode dropping the load on the generator so it's loafing. You might as well be using solar for that low current.

hclarkx · 01-25-2021, 11:00 AM

I slept on what I said above. There's a much better way.

Run your generator in the morning, along with the solar, until the battery voltage hits about 14.4 Volts. At that time the battery is ready for the absorb stage which the solar can handle (if there's sun and not too many clouds and enough solar) so you can turn the generator off.

The SOC Should read 75-80% or at least between 70 and 85% (depending on battery age, battery chemistry details, etc) when voltage hits about 14.4. If it isn't in this range, the BMV settings are not correct or the BMV has not been resynch'd in a while.

Since the SOC is not reset/resynch'd until the end of the absorb stage it's a much less accurate way to judge when the generator can be turned off. The voltage hitting 14.4 signals the end of the bulk stage very accurately.

vsheetz · 01-25-2021, 11:19 AM

Review your parameters.

The monitor automatically sets 100% SoC when the Charged Voltage AND the Tail Current have been met for the Charged Time.

Set charged voltage at about .2v below the charger absorb voltage. Tail current at 2% for lithium, 4% for lead acid. And time at the default of 3 minutes. Adjust from there as needed.

You can tell when 100% was set on the history tab - last full charge.

Additionally. Turn off start synchronized. This will confuse if the monitor is restarted for any reason.