Batt voltage looks good but no power

Re: Batt voltage looks good but no power

Offgrider9 wrote: »

Disclaimer: Not really new to solar but new to forum and new to off-grid living...


The battery voltage climbs healthily during charging either from the solar or the genset and seems to come to rest at about 26v. But when the sun goes down and/or the genny stops, the inverter shuts off and the power goes out. Basically, under load the batteries fail to produce any current.

The old battery bank that I replaced with the new Crowns was performing ok for a while but eventually the same thing happened with those. We would see a rapid rise in battery voltage as soon as the sun came up on the array. Then a rapid decline in voltage as soon as the sun went down. Battery storage capacity has left the building. I am apparently a very good destroyer of batteries despite the fact I do keep an eye on the water level, equalize them about once a month, have low voltage shut-off points set on the inverter, and have set the charge points on the controller according to all the literature I read on proper battery use.

I know enough to be quite dangerous but I really need to learn more to get past the point of being dangerous and delve into the realm of being useful. Any help along these lines is greatly appreciated. I apologize for redundancy if any threads have been posted about this in the past; please direct me to those.

Thanks!

Eric

Where are you measuring the battery voltage? At the battery terminals themselves or at the CC? Are you just reading the built-in voltage display of your CC?

Where did you get the idea that 26 volts during the charge cycle is a good endpoint?

While you are charging, for typical Trojan batteries, the voltages should get to about 29 volts during the Absorb stage of charging and not drop back to a Float voltage of ~ 26.4 until the batteries are essentially fully charged.

The recommended voltage for Equalize is around 31 volts, if you can get that high while staying within the current limits.

It looks like what you are doing is chronically undercharging your batteries, causing them to continuously lose capacity until they are essentially dead. Even a battery with no useful capacity left will let you get up to 26 volts during charging, but will not really be accepting current or developing capacity.

Now that all of the discussion of voltage is done, since you are using vented cells, you MUST measure the Specific Gravity (SG) with a temperature compensated hydrometer (or manually apply a temperature correction.) Fully charged SG will vary by battery type, but will generally be in the area of 1.250 to 1.270 (consult the literature from Crown for accurate numbers on your batteries.)
(To the extent that it is useful at all, the only voltage indication which is meaningful without calibration against SG measurements for your batteries, is the resting voltage. The batteries should be neither charged nor discharged for three or four hours before making that measurement. You are relying on expensive equipment (ammeter and battery meter) which are not suited to this particular job rather than getting the inexpensive (as low as $10) tool that is critical.)

I think you will find your SG to be much lower than that, indicating that your batteries are essentially boat anchors already. (Although use of lead for boat anchors is not environmentally sound.)

You may be able to at least partially rescue them with a long term regime of Absorb and Equalize charging at much higher voltages than you are using now, but that may best be done by moving the batteries to a place were you have POCO power, or else planning to devote several weeks of solar PV charging to the task.

If you carefully read advice on the battery voltage settings you need, it appears that either you read some really bad sources or else you misinterpreted what you read. It is also possible that there is a high resistance in the wiring between your CC and your battery bank, causing the voltage seen at the CC during charge to be much higher than the voltage at the battery terminals.

Since your PV will only charge the batteries for a limited number of hours each day, you do not have enough hours in a day at the Float setting to properly charge your batteries, even if you did not discharge them each night.

Re: Batt voltage looks good but no power

I would run over to O'Rielly's auto parts(Grass Valley, CA) and buy a hydrometer that looks like this;


Attachment not found.

Picture should be a link, I'd recomend ordering one from our sponser but you need info quickly. remove the foam prtecting the inner glass from the outer glass. Buy a couple gallons of distilled water, wash out the hydrometer a couple times before using and between testing each cell. I have purchased a couple of these and they mirror my higher quality hydrometer very closely. Be careful the inner glass 'float' is made of very thin glass and breaks easily. When you done wash out the tube a few times and let drip. I put mine in an empty gallon jug and leave it there until the next use, the bottom of the bulb fits closly to the top of the jug.

Re: Batt voltage looks good but no power

Offgrider9 wrote: »

So, is there still hope or am I looking at a probable bank replacement...again?

Goofy thing is, you might return them and plead ignorance and since they are under warranty, they may be covered. Sometimes, even abused, warranties are honored for assorted reasons....

...worth a try.

BTW, those hydrometers are in stock, and they are open 8am to 8 pm Sunday at 121 Olympia Park Road - Grass Valley, CA, just since I had the web site open, they're even cheaper than here in mid Missouri!

Re: Batt voltage looks good but no power

I'm with Photowhit, time IS a wastin'. Go out today and get that Hydrometer. If there is a close neighbor, try borrowing one NOW.

Look for Crown's Battery Manual (or similar name) for EXACT charging parameters.

For almost all FLA batteries(ones with removeable caps), EQ should be around 31 V. Be sure that you are using a Battery Temp Sensor attached midway down a battery near the center of the bank.

Make certain that the charge voltages are set correctly on each charge source, and generally, each charge source needs its own BTS, although OB Inverters and CCs can share one if you have the correct giblets, and use the correct ports for them.

For now, increase the Absorb voltage on the CC, and would recommend increasing Absorb times to HOURS and HOURs. Little to loose at this point.

Most of this has been covered by others. Good Luck. Two Hydrometers or three is a good thing. Vic

Re: Batt voltage looks good but no power

Offgrider9 wrote: »

I have a Bogart Trimetric but I don't think it's reliable. I need a good battery monitor.

The trimetric is a good monitor.

A battery monitor is often compared to the gas gauge in your car, but that is not a good analogy.

The gas gauge in your car actually measures the amount of gas in your tank. A battery monitor doesn't measure anything. It is more like the odometer in your car. The odometer counts miles and the battery monitor counts ampHours.

Suppose you have a car that gets about 25 mpg and has a 15 gallon gas tank. Suppose also that your gas gauge does not work. What do you do? You use your odometer. For example: After a fill up you drive 150 miles and you expect that you have used 6 gallons and have 9 gallons remaining in your tank.

If you fill up the tank again you can, as above, use your odometer to estimate your gallons remaining.

But what if you do not completely fill your tank. For example, starting from a full tank you drive 150 miles and then you add 3 gallons to your tank and then drive 100 miles and then add 4 gallons to your tank and drive 150 miles and then add 5 gallons to your tank and drive 100 miles. At this point you estimate that you have 7 gallons remaining in your tank, but that estimate is not too accurate because your mileage is not ever exactly 25 mpg. Mileage depends on many factors: how much idling, how fast you drive, how fast you accelerate, temperature, etc.

So it is with your battery monitor. It counts ampHours in and out. It does not take into account the effect of temperature on battery capacity. It assumes that 1 amp for 100 hours is the same as 100 amps for 1 hour (its not the same...Peukert effect). It does not even know the ampHour capacity of your battery (other than what you tell it), and that capacity varies with age, temperture and sulfation of the battery.

Your battery monitor works like the odometer... when you fill up the gas tank you reset the odometer. When you fill up your batteries the battery monitor is reset. Your battery monitor will reset itself when the batteries are full, but you have to program it to know when the batteries are full. Without a hydrometer or refractometer you don't know when your batteries are full.

Over on the outback forum it is commonly written: "lie to your battery monitor and it will lie to you". In other words, have you programmed your trimetric properly?

Bottom line: the longer its been since a complete charge, the less you can trust your battery monitor. And you can't trust it at all if its not set up correctly. That said, battery monitors are valuable tools in estimating your SOC, but you have to understand their limitations. You must have a hydrometer or refractometer, and then you and your monitor learn how to estimate your SOC without having to use the hydrometer every day.

--vtMaps