|
| Author |
Message |
Sleeping Bear
Member
|
# Posted: 1 Jul 2013 12:04
Reply
I have a small cabin PV system consisting of (2) 135 watt Kyocera Panels, connected to a Morningstar PS-30M charge controller and (4) Universal Batteries 90 A/H batteries. I use this to power 12volt led lights and a 12 volt Sure Flo pump. Everything works fine and has been for some time except for the Sure Flo pump. The charge controller will read 14 plus volts on the battery bank when the pump kicks on it will run for approx. 2 1/2- 3 minutes to charge the pressure tank for my water system and the charge controller will drop to yellow and approx. 12.2 volts. I have checked all of the batteries with a loaded voltmeter to make sure that they are good with no bad cells. The pump circuit runs on 14 ga. wire. I am confused as to why such a large voltage drop in a short period of time. The pump only shows to draw 6-9 amps.What am I missing? I know their are a lot of Smart people on this forum and I am hoping that they can help me solve my dilema. Thanks in advance
|
|
VTweekender
Member
|
# Posted: 1 Jul 2013 12:13
Reply
Hi, please explain exactly how your battery bank is connected together..
|
|
Truecabin
Member
|
# Posted: 1 Jul 2013 13:09
Reply
you wrote everything has been working fine you dont say how old the UB batteries are, do UB brand last longer than a couple years?
check voltage across each connection in every component, even between the batteries during the 2-3 minutes the pump is running if the connections are good there will be zero volts across a good connection.
or maybe one of your batteries has no capacity
|
|
GomerPile
Member
|
# Posted: 1 Jul 2013 13:53
Reply
*** 2 Issues ***
1)
+ 14 AWG wire is .252 ohms per 100ft.
+ Assuming a 50 ft run to your pump motor
+ VOLTS = AMPS x RESISTANCE or .252 x 9 = 2.268 V
In english: the wire run to your motor is too small...you are losing 2.2 volts across it.
2A) *IF* your charge controller is at the end of a long run of wire then it is simply seeing the voltage drop and indicating yellow because you are droping a lot of voltage across your wiring.
2B) [most likely issue IMO] *IF* your charge controller is connected close to your batteries its seeing the battery voltage drop as the pump discharges your batteries.
Check the water level. Check the terminals for corrosion. Try the battery from your car and see if the issue goes away.
|
|
Sleeping Bear
Member
|
# Posted: 1 Jul 2013 14:12 - Edited by: Sleeping Bear
Reply
The wire run to the pump from charge controller is 16 ft. The wire run from the battery bank to the charge controller is 3 ft. What size wire would you recomend I change to.
According to your math above it is 2.26 volts of resistansce for 100 ft. which would be .023 volts per ft. x 16 feet for a resistance of .36 volts. correct? or am i looking at it wrong.
I agree that I may need a larger wire size I am just not sure What size and copper is to expensive to be experimenting with.
|
|
GomerPile
Member
|
# Posted: 1 Jul 2013 15:30
Reply
16ft times 2....(total of 32ft of wire).....or .72 volts.
I would use 10 or 12 AWG wire....solid romex is fine. I have also used low voltage landscape wire but its not close to code  .
|
|
GomerPile
Member
|
# Posted: 1 Jul 2013 15:35
Reply
If you have a volt meter you can measure the voltage directly at the battery terminals and compare it with the voltage at the terminals of the charge controller. The difference is getting lost in the wiring.
If your battery voltage is droping while the pump is running its probably the battery. Swapping your car battery is a great way to test. Do check the water levels, I had a battery go low and it behaved in a similar manner.
|
|
cman47c
Member
|
# Posted: 1 Jul 2013 15:40
Reply
Does the voltage read 12.2 while the pump is running or after the pump has shut down? The load will pull down the battery voltage while running, but if the batteries are in good shape they should go back to their actual state of charge voltage when pump has stopped. 12.2 volts is about 50% charged, and the yellow light indicates 50% battery state. The fully charged battery should be above 12.7 when no loads are on. I would add that a 9 amp draw is quite large but your pump run time is quite brief so if your batteries and charging system are in good shape, that would not be a problem unless the pump runs many times in one hour.
|
|
|
Truecabin
Member
|
# Posted: 1 Jul 2013 16:22 - Edited by: Truecabin
Reply
to save $ you can use all 3 wires of romex housewiring for the plus and another separate cable for the minus, its a good use of old wires.
if you use 2 of the "12-2" wires for plus (for example white and bare) and the other one for minus every bit of copper you add makes the pipe bigger and flows more but if you can find 12-3 thats better (4wires) plus you will feel better
|
|
ICC
Member
|
# Posted: 1 Jul 2013 17:42 - Edited by: ICC
Reply
Quoting: Sleeping Bear The wire run to the pump from charge controller is 16 ft. The wire run from the battery bank to the charge controller is 3 ft. What size wire would you recomend I change to.
That confuses me. There should be no direct run from the CC to the pump. The CC should be wired directly to the batteries and the pump should be wired off the batteries on it's own wires.
My electrical design calculator gives me 8 gauge wire for 12 VDC running 16 feet of copper (one way), with a maximum current draw of 10 amps and limiting voltage drop to 3%. 3% voltage drop is a good goal for low voltage DC circuits.
It is expected to see the battery voltage drop while a heavy load is applied to the battery. The voltage should recover when the load is removed if the batteries are in good condition and the charge has not been depleted much. 2 or 3 minutes at 10 amps should not severely deplete a healthy battery.
Q? are those batteries flooded cells? If so test with a hydrometer to see if they really reach a full charge. If those are not true deep cycle batteries and more than 2 years old they may be dieing. Depends a lot on temperatures that the batteries live in; elevated temps kill batteries.
|
|
Martian
Member
|
# Posted: 1 Jul 2013 18:40 - Edited by: Martian
Reply
First off, the voltage drop, across the wires, is felt at the load...not the batteries. If the voltage is dropping at the batteries, you have one or more bad batteries, and if a battery reads 12VDC, then it is already 50% discharged. A fully charged battery will read close to 13VDC one hour after the charger is removed.
While most batteries, used in a non-vibration application, will last 4 years or more, it is not uncommon to have one go bad in less than a year.
Amperage is measured in hours. Therefore, if the pump runs for 3 minutes and pulls 9A, it is only removing .45 amps from the battery. If that is pulling your 360AHr battery bank voltage down, you definitely have a bad battery, or several bad batteries. Also, sensing wires carry very little amperage as there is very little current flow to a sensor. Therefore, you don't need a big wire to sense the battery charge.
Every month, while managing a yacht repair yard, I wrote an article for a sailing magazine on yacht repairs. My closing line was, "Don't forget to check the water in your batteries" because batteries die quickly if the water gets low, and they aren't cheap!
Tom
|
|
ICC
Member
|
# Posted: 1 Jul 2013 19:03 - Edited by: ICC
Reply
If those "Universal Batteries 90 A/H" are the same as this one then you cannot use a hydrometer or check the fluid levels. In that case all you can do is go by voltage. Read the volts after the batteries have been at rest for several hours; no charging, no discharging.
IMO, it is best to NOT use gel cell batteries off grid. Gel cells are more sensitive to overcharging and to deep discharging. Best bang for the buck are 6 volt golf cart batteries bought at a warehouse store like Costco, Sam's, BJ's.
If your batteries are NOT gel-cells disregard the above gel-cell rant.
Quoting: Martian Amperage is measured in hours. Therefore, if the pump runs for 3 minutes and pulls 9A, it is only removing .45 amps from the battery.
mmmm... not quite.
Current is measured in amps (or amperes) and current itself has nothing to do with hours. A current of 9 amps means that 9 amps is flowing through the circuit right now. Turn it off and current is zero.
If the current was to flow for 1 hour that would be a power consumption of 9 amp-hours. For only three minutes that power would be 0.45 amp-hours. The numbers are the same but the terms 'amps' and 'amp-hours' were listed incorrectly. Sorry but I am anal on stuff like terminology.
|
|
Martian
Member
|
# Posted: 1 Jul 2013 22:02
Reply
"In practical terms, the ampere is a measure of the amount of electric charge passing a point in an electric circuit per unit time with 6.241 × 10 to the 18th electrons, or one coulomb per second constituting one ampere."
This is the basic definition of an amp taken from Wiki. My understanding is that in one hour's worth of seconds, the number of electrons passing a point from a battery to power something will equal the amperage rating of a piece of equipment. A 20Ahr battery has enough electrons stored to power a 1A load twenty hours or a 20A load for one hour. I was referring to the rating of the pump which is how many amps it will draw in one hour of running.
Tom
|
|
ICC
Member
|
# Posted: 2 Jul 2013 01:29 - Edited by: ICC
Reply
I think the tech definition in wiki leads to confusion..... how many people really know coulombs and electrons per second. In terms practical to the DIY world of off grid electricity it is best looked at in simplistic terms, We have 10 amp fuses for example. Not a 10 amp per hour fuse. PV panel specs list amperes; short circuit amps, maximum power amps; amps on amp-hours.
Quoting: Martian A 20Ahr battery has enough electrons stored to power a 1A load twenty hours or a 20A load for one hour.
Correct, with a 'but'.. One more piece of info is needed to make that even a better description. The battery amp-hour rating is given for a specific discharge timeframe. For alt energy systems that is a 20 hour rate. Some ratings use a 100 hour time. This is an important differenceas the total watts that can be removed from the battery falls as the ampere rate increases, and vice versa, meaning that the 1 amp for 20 hours should be just about right, but if 20 amps was the load the battery would be discharged before that hour is up. Theory says one thing, real world performance is another. The Trojan battery website indicates different amp-hours for 5, 20 and 100 hour rates. http://www.trojanbatteryre.com/Products/Products.html?tab=0#TabbedPanels1#top
5 hours = 185 amp-hour rating
20 hrs = 225
100 hrs = 250 amp-hours
Quoting: Martian referring to the rating of the pump which is how many amps it will draw in one hour of running.
That is right and wrong Tom. An ampere (amp) is an instantaneous reading or figure. Amp-hours is the total amperage taken over a period of time. Just as amps x volts = watts, the amp-hours x volts = watt-hours.
Any piece of equipment that has an amp rating on the label will draw that amperage (in theory) at any point in time when it is operating. I have a pump that is rated at 6.5 amps at 40 psi and a flow of 1.5 GPM on 12 volts DC. That means any time it is running at that rate and pressure an ammeter should read 6.5 amps. If I leave it on for an hour it draws a total of 6.5 amp-hours, not 6.5 amps. If it runs for ten minutes it draws 6.5 amps for every second it runs; making 0.65 amp-hours of power used.
The 6.5 amps figure is what we would use to calculate the size of wire required for a certain length run of wire. Just because the 10 minute amp-hour use is 0.65 amp-hours does not mean we can reduce the wire size by using the smaller amp-hour value. When the pump runs the wire needs to be large enough for the 6.5 amps to be safe and to allow the pump motor to operate efficiently.
Sorry if it seems like I'm nit picking. It's just that it seems electrical is enough of a challenge to may people and I try to make it simple as possible. It's an area that is easy to get lost and confused in.
Ike
|
|
Martian
Member
|
# Posted: 2 Jul 2013 08:23
Reply
Ike, did you work for the government?
We have a guy who is trying to figure out if his batteries are bad. The wiring size, or fuse/breaker size, really don't matter in solving his problem. He just wants to know why his batteries indicate a low charge after a relatively minor draw has been placed on them. Having lived with batteries as my power source for many years, I was trying to answer his question in the simplest terms possible. Based on my experience, he has a battery problem which needs to be solved to correct his problem. Either his batteries are not fully charged, or one or more of them has a problem, is my guess. It could be something as cheap to fix as dirty connections, or as expensive as replacing all the batteries.
In troubleshooting this problem, I would separate the batteries, fully charge each one, wait a 24hrs, and then load test since he can't do a specific gravity test of each cell as they are sealed (based on your information about the batteries.)
As much as I would love to continue this discussion with you, I must leave for work. Hopefully, he hasn't found our discussion too confusing. Have a great day.
Tom
|
|
Sleeping Bear
Member
|
# Posted: 11 Jul 2013 15:34
Reply
This discussion is most helpfull. My background is in mechanical design. I understand the basics of electricity and that is about it. I have been gone to my cabin for the last few days and everything is working fine. The pump will draw down the voltage when it is running but will rebound back within a short time after the pump shuts off. Sometimes my meter will indicate yellow when the voltage drops to about 12.5 volts other times it indicates yellow at 13.2 volts then the next day it will indicate green at 12.2 volts. I have a feeling that my problem is a little of everything that has been discussed. My current plan is to get a new charge controller, a new battery, and a new solar panel and run the pump as a totally seperate system all by itself. I have never run out of power or had the system shut down because of low voltage but watching the meter indicates that I have a problem and it could just be the meter is bad. I travel 1400 miles one way to my cabin so if my water or power are not working I just have to make do.
Thanks for all the ideas.
|
|
creeky
Member
|
# Posted: 12 Jul 2013 09:39
Reply
sleeping bear. the morningstar controller shows yellow when it is out of float. if I remember correctly. It should show yellow red or red if its at 12.2.
As cman47c points out. your voltage at the batteries will drop during and just after load. ie. the pump is running.
it sounds to me like you're watching the lights too much! I was concerned this year when I saw my morningstar flashing green. Of course, then I checked the manual and it said, flashing green indicates the battery is charging. Oh. I sez to myself.
The best bet would be to check your batteries when you first arrive at the cabin. no lights. no pump. etc.
Of course an mppt controller, new flooded cell batteries, and another panel are all great additions. good luck.
|
|
|
