Newbie question

vtmaps

Re: Newbie question

waynefromnscanada wrote: »

Easiest way to think of deficit charging:
Deficit charging happens when over an extended time, you continue to take more OUT of the batteries than you put back IN, regardless of the size of the batteries.

That is true, but not the whole story... To avoid deficit charging you need to put in MORE than you take out. And if you put it in at too low a current, it doesn't matter how much you put in... it will never be fully charged. Gene is correct that a smaller battery is less likely to be deficit charged in any given system. Of course, if the battery is too small (and therefore too deeply cycled) it may not outlast the larger, but deficit-charged battery. Its all about perfect balance.

--vtMaps

gww1

Re: Newbie question

Coot

My preferred short cut here is to use the nominal system Voltage as the low point, as it pretty much ensures the battery will not be discharged below 50% under load.

So on a 48 volt bank set "re-bulk" and "low voltage cut off" to 48 volts and that will keep your batteries from ever being discharged below 50%?

Thanks
gww

Cariboocoot

Re: Newbie question

gww1 wrote: »

Coot

So on a 48 volt bank set "re-bulk" and "low voltage cut off" to 48 volts and that will keep your batteries from ever being discharged below 50%?

Thanks
gww

That's the process. A nominal "at rest Voltage" is about 50% SOC, so if you stop draining it at that level while under load the batteries should "rebound" a bit above that. Most LVD's have to be "so much" below the cut off point for "so long" before they will shut down, so the occasional drop below nominal for a start-surge will not shut the system down.

Talking in generalities again; can't say for sure it will work on every inverter in the world.

gww1

Re: Newbie question

I love rule of thumb for dummy type safety nets. It is a great place to start and then work from.

Thanks
gww

Gene.243

Re: Newbie question

I'll go with the smaller batteries so I can be more assured of keeping them fully charged.
I need my combiner box and CB box first.

Gene.243

Re: Newbie question

There has been a little headways on the solar system. We managed to get the panels on the roof yesterday. I can say PITA but they are up and secure. Combiner box will be delivered soon.

Gene.243

Re: Newbie question

Update,
The system is assembled and charging my camper battery. I'm leaning toward 4 Trojan L16's at 325 Ah. My steady load is down to 60 watts so I should be able to keep the pumps running for a few days with no sun.

vtmaps

Re: Newbie question

Gene.243 wrote: »

Update,
The system is assembled and charging my camper battery. I'm leaning toward 4 Trojan L16's at 325 Ah. My steady load is down to 60 watts so I should be able to keep the pumps running for a few days with no sun.

Congratulations. Have you thought about adding a battery monitor to your system? Its a great way to keep track of things when the sun isn't shining for a few days. Also, and even more important, do you have a hydrometer or refractometer?

--vtMaps

Gene.243

Re: Newbie question

Went and bought a hydrometer Saturday. I don't know what the SG was to start with but I topped off the water level and started charging the battery. Once it was in float charge I hooked up the inverter and powered my water pumps. The charger stayed in float until sunset and the battery powered the system all night. The volts were at 11.9 when the sun started shining and the charger started picking up the load and charging the battery. That afternoon I bought the hydrometer and tested the battery. I observed readings around 1.14. Way in the bad range but the volts read 12.5. So my voltage says 75% to 80% charged but my SG says 25% charged. I'm confused. I didn't run much load to remove the surface charge so my VOC may be high. But even after a 1 hour equalize charge at 14.4V the SG is still only 1.16. Is it charged or not?

Cariboocoot

Re: Newbie question

Okay, so some procedural errors.

"I don't know what the SG was to start". Best case: fully charge batteries before any use, measure and record SG.

"I topped off the water level and started charging the battery". No, you want to charge a battery before adding any water. Never add water to a discharged battery unless the plates are exposed, and then add just enough to cover (and keep covered) until it is charged. You never know how much sulphur is lurking on the plates and how much the SG will shift by adding water.

"The volts were at 11.9 when the sun started shining". This sounds like you are using too much power overnight.

"But even after a 1 hour equalize charge at 14.4V the SG is still only 1.16. Is it charged or not?" No, it's not. It may even be damaged.

Voltage can be an indicator of SOC only when the battery is resting for hours (no current in or out). What is worse is that a bad battery can zip right up in Voltage, appearing to charge, but has no capacity due to being sulphated. It's like thinking you have a 'D' cell and finding out it only has the power of an 'AAA': Voltage is the same, but the power isn't there.

Now, what batteries did you actually get? If they are four Trojan L15A's @ 325 Amp hours configured for 12 Volts they need 65 Amps peak charge current, and about three hours in Absorb @ 14.8 Volts under normal conditions to charge properly. Are they getting that?

vtmaps

Re: Newbie question

Gene.243 wrote: »

Went and bought a hydrometer Saturday.
<snip>
That afternoon I bought the hydrometer and tested the battery.

I'm confused. Yesterday (Sunday, Sept 1) you wrote: "I'm leaning toward 4 Trojan L16's at 325 Ah". What battery were you testing on Saturday, Aug 31?

--vtMaps

BB.

Re: Newbie question

Was that 12.5 volts when the solar array was charging the battery bank? If so, then either you don't have enough charging current and/or those batteries are quite deeply discharged.

In general, a decent hydrometer with temperature corrected readings is the "gold standard" for estimating battery state of charge.

To understand your battery state of charge with a volt meter, you need to know if it is charging/discharging/resting voltage?

-Bill

Gene.243

Re: Newbie question

Let me apologize for the confusion. I am using my camper battery until I can purchase a good set of batteries. This battery is a DC24. Your typical mass produced deep cycle marine battery. Not a good battery just what is on hand. I'm too excited to wait.

Cariboocoot

Re: Newbie question

So you won't be too disappointed to find out it's toast?

These things are usually about 90 Amp hours, and if it's older it will be less than that. This would explain many of the symptoms you are experiencing.

Gene.243

Re: Newbie question

It's less than a month old.

Photowhit

Re: Newbie question

Gene.243 wrote: »

Went and bought a hydrometer Saturday. I don't know what the SG was to start with but I topped off the water level and started charging the battery. Once it was in float charge I hooked up the inverter and powered my water pumps. The charger stayed in float until sunset and the battery powered the system all night. The volts were at 11.9 when the sun started shining and the charger started picking up the load and charging the battery. That afternoon I bought the hydrometer and tested the battery. I observed readings around 1.14. Way in the bad range but the volts read 12.5. So my voltage says 75% to 80% charged but my SG says 25% charged. I'm confused. I didn't run much load to remove the surface charge so my VOC may be high. But even after a 1 hour equalize charge at 14.4V the SG is still only 1.16. Is it charged or not?

You show a lot of confusion here, Coot helped you with some of it, I would suggest your confusion about EQ (equalizing) would indicate that you haven't read through the FAQ's. NAWS (Northern Arizona Wind and Sun) provides some great information about batteries and other parts of Solar electric systems here.

Equalizing has to be done once your battery is fully charged, and a single reading provides little help, in a correction EQ cycle you measure all the cells and maintain an equalizing charge (higher voltage) until they no longer rise, checking once an hour or so until there is no rise over an hour or 2.

14.4 volts for a 12 volt battery would be considered a normal absorb level for many/most flooded lead acid batteries. EQ usually is 10-15% higher

Gene.243

Re: Newbie question

I'll get some reading done.

Skippy

Re: Newbie question

This raises one question I have. If I may add it here ?

The O.P states that he is thinking of getting a battery bank sized at - 220 AH @ 24 V - but for now, has connected a 90 AH 24 V battery.

Question is, that would be WAY too small for the amount of power going in (wouldn't it ? 90 AH instead of 220 AH), so can you "cook" a small battery with too much current going in to charge ? or would the charge controller limit the bulk charge ?

I have been thinking the same thing, put a small battery on the large system, run small loads for now, and put in bigger batteries when possible, but figured that the large system would put out large amperage, and cook the smaller battery. Correct ?

Thanks for including that link, I will check it out as well.

Cariboocoot

Re: Newbie question

Skippy;

You are correct that it is possible to put too much current to a small battery and cook it. However, to some extent this process is self-limiting. As the Voltage comes up the current goes down. In the case of a very small battery this will happen very quickly and so the time spent at high current should be very short; once Absorb Voltage is reached the current will be lowered considerably to maintain that Voltage.

If this were a constant-current charger as used in commercial applications the battery would suffer worse.

Of more concern is what is happening due to the heavy discharge between rechargings.

Gene.243

Re: Newbie question

I'll change the settings on the charge controller tomorrow. I'll limit bulk charging to 10 amps. ( C20/8. ) set the absorb voltage to 14.7 (typical FLA) and float to 13V Temp. compensation will drop that to 12.6. This is for my camper battery as all I know is that it is size group 24 and they are usually 70 to 90 AH at 20 hrs. The factory default settings were "causing" the confusion. I think...
Thanks for the input guys.

westbranch

Re: Newbie question

Another reason for the low SG ma be that there was not enough mixing of the fluids in the battery by such a short EQ, if an EQ actually occurred (too low a voltage?). The batteries should bubbly vigorously in EQ thus mixing all the fluid in each cell

Gene.243

Re: Newbie question

This system will not get batteries for a little wile as I will be getting a rotator cuff repaired next week and will be one handed for a wile. Thanks for all the input I'll get batteries when I can handle them.

Cariboocoot

Re: Newbie question

Gene.243 wrote: »

This system will not get batteries for a little wile as I will be getting a rotator cuff repaired next week and will be one handed for a wile. Thanks for all the input I'll get batteries when I can handle them.

Sorry to hear that. I'm in much the same boat; I've been one-armed for three months now. Specialist is supposed to look at it next week. :roll:

Gene.243

Re: Newbie question

My nearest battery dealer sells Exide batteries. Do they have a reasonable reputation?

Cariboocoot

Re: Newbie question

Gene.243 wrote: »

My nearest battery dealer sells Exide batteries. Do they have a reasonable reputation?

Whereas I haven't seen any in years they always were a top quality brand when available.

Anyone have any recent experience?

Gene.243

Re: Newbie question

Now I'm leaning toward some Exide L16s. I wish their data was freely available like Trojans.
Surgery is done. Let the healing begin.

niel

Re: Newbie question

even when you think it's healed, give it more time.

Gene.243

Re: Newbie question

Still giving it more time. Don't feel like wrestling any L16's. This was a bite from a F-16.