New Issue Question - Battery Not Charging

Red BaronRed Baron Registered Users Posts: 5
We use Northern Arizona's 1 watt solar panel and SunGard charge controlled, coupled with an 8 amp Power Patrol battery and relay to rrun a 1.9 amp bilge pump. They work fine much of the time but eventually the battery stops fully charging and shows just 5 volts...not enough to activate the relay or start the bilge pump.

The batteries are new and seem fine, and were taking a good charge from the solar panel before, but eventually the charging seems to stop.

Any ideas on trouble-shooting? I have checked the relays, they're fine.

Comments

  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: New Issue Question - Battery Not Charging

    a 1 watt solar panel is insufficient to supply enough power to run such a pump let alone charge the battery. the battery too is undersized for the load. most batteries are considered dead at 10.5v and going down this far or farther will shorten the lifespan of the battery if it isn't already ruined. knowing the power requirements of the load is vital in planning a good system to operate it.

    what you are doing is equivalent to trying to pull a truck with a go cart as it might move it at first, but is short lived due to the strain.
  • Red BaronRed Baron Registered Users Posts: 5
    Re: New Issue Question - Battery Not Charging
    niel wrote: »
    a 1 watt solar panel is insufficient to supply enough power to run such a pump let alone charge the battery. the battery too is undersized for the load. most batteries are considered dead at 10.5v and going down this far or farther will shorten the lifespan of the battery if it isn't already ruined. knowing the power requirements of the load is vital in planning a good system to operate it.

    what you are doing is equivalent to trying to pull a truck with a go cart as it might move it at first, but is short lived due to the strain.

    Sorry, I left out an important part of the equasion probably. The pump needs to run infrequently - maybe for 30 minutes once per 10 days. A full battery will run the pump about 10 hours, so rarely will the battery be fully discharged.

    I have recharged the battery and it is fine. I tested the system numerous times by letting the pump run until the battery was dead, then set the unit in the sun to recharge for various lengths of time from 1 hour to several days. Each time the solar panel charged the battery, but to varying degree according to the charge time of course.

    It seems as though at some point it decides to stop charging the battery.

    Still perplexed.
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: New Issue Question - Battery Not Charging

    what is the power requirements of the pump?

    to say you don't understand because it is sized properly is not likely to be correct. a battery drained to 5v says something is very wrong even if it were to only turn out to be the 1w pv at fault as the pump could have been reliant on the stored power that the battery had, emphasizing past tense. 1w/14.4v=.069a. no way will this be good to charge a 10ah battery. the range of recommended charge is 5%-13% for .5a to 1.3a. some have gotten away with as low as 3% to long term charge a battery, but i don't recommend that and that would be .3a for that battery.

    we still don't know if the battery is properly sized either as 10ah seemed quite small to me.
  • Red BaronRed Baron Registered Users Posts: 5
    Re: New Issue Question - Battery Not Charging
    niel wrote: »
    what is the power requirements of the pump?

    to say you don't understand because it is sized properly is not likely to be correct. a battery drained to 5v says something is very wrong even if it were to only turn out to be the 1w pv at fault as the pump could have been reliant on the stored power that the battery had, emphasizing past tense. 1w/14.4v=.069a. no way will this be good to charge a 10ah battery. the range of recommended charge is 5%-13% for .5a to 1.3a. some have gotten away with as low as 3% to long term charge a battery, but i don't recommend that and that would be .3a for that battery.

    we still don't know if the battery is properly sized either as 10ah seemed quite small to me.

    Thanks. The formulae is over my head, obviously. Would a 5 watt solar panel be sufficient?
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: New Issue Question - Battery Not Charging

    5w would not suffice. 5w/14.4v=.347a and would not be good for that is under the 5% minimum i'd recommend.
    let's start at the beginning with the load. what are the electrical requirements of the pump?
  • BB.BB. Super Moderators, Administrators Posts: 28,160 admin
    Re: New Issue Question - Battery Not Charging

    A good size panel for a 8 AH 12 volt battery would be:
    • 10 AH * 14.5 volts * 0.10 rate of charge * 1/0.77 panel+chrgr derate = 15 watts
    How much power you need to power your pump--10 hour run-time on a 8 AH battery:
    • 8 AH / 10 hours = 0.8 amp average load
    How much solar panel to run the pump:
    • 0.8 amps * 1/2 hour per week * *1/7 days per week * 12 volts * 1/0.77 eff * 1/0.80 batt eff * 1/2 hours of sun minimum per day in winter = 0.6 watt panel
    So, from a simple energy required per week to run the pump, the 1 watt panel would be enough (based on 1/2 hour per week).

    One problem is that you do need a 8 AH battery to run a 0.8-1.9 amp load (too large of load/too small of battery would have voltage collapse to run your load). (note, for centrifugal pumps, such as your sump pump, reduced flow from pumping water up hill/through small lines does reduce average current draw).

    So, it would appear that your panel requirement is driven by the size of the battery... A 8-15 watt panel (5%-10% rate of charge) would be a better fit.

    One loss that may not be accounted for is that a small lead acid battery may loose upwards of 1% state of charge per day:
    • 8 AH * 12 volts * 0.01 = 0.96 watt*hours per day
    If you only have 2 hours of sun in the winter, then to keep up with self discharge:
    • 0.96 WH discharge per day * 1/0.77 derating * 1/2 hours per day of sun = 0.7 Watt Solar Panel
    So--your 1 watt solar panel is just able to keep up with the self discharge of the 8 AH battery, and not really provide enough energy to keep up with the solar pump.

    An 8-15 watt solar panel is really overkill--but for a reliable system with some backup capabilities (what if there is a leak/rain/etc. that needs more pump run-time), it is certainly justifiable.

    If you are using a charge controller (like the 4.5 amp rated SunGuard controller), make sure the Vmp of the solar panel is somewhere around ~17.6 volts... Many small panels are intended to connect directly to the battery without a charge controller and have Vmp~15 volts (sometimes called a self regulating panel).

    The Vmp=17.6 volt + controller setup will be much more reliable (energy production wise) for you.

    -Bill

    PS: Watch your 8AH battery... I don't trust batteries that have been taken to "dead"--There is a chance that one or more of the cells have been reversed charged (5 "good cells" can drive current backwards through the one "weak cell" which usually ruins that cell because the cell is subject to a reverse voltage charging current). If the battery is over 1 year old--I would replace it. I have seen batteries run dead that will work OK for a couple of weeks, then die again with no warning (typically happens with car batteries).
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: New Issue Question - Battery Not Charging

    my error in misreading the battery to be 10ah, but you still need to address first things first and that is the actual load.
  • Red BaronRed Baron Registered Users Posts: 5
    Re: New Issue Question - Battery Not Charging
    niel wrote: »
    5w would not suffice. 5w/14.4v=.347a and would not be good for that is under the 5% minimum i'd recommend.
    let's start at the beginning with the load. what are the electrical requirements of the pump?

    Pump is:
    12v DC
    Amp Draw: 1.9 @ 12v
    Fuse Size: 2.5 amps

    We use a DPDT 12v relay, and a reed type float switch.

    We haven't been using a fuse - don't know if that has anything to do with our issue.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: New Issue Question - Battery Not Charging

    Two Canadian cents worth of opinion here. :p

    A 1 Watt panel won't do anything for you. The old notion that you can recharge a lot of battery with a little panel given enough time has proven to be false; the battery fails. 1 Watt likely won't even keep ahead of self-discharge, much less provide any real charging. Like Bill says, you'd need about 15 watts.

    A 12 Volt battery drawn down to 5 Volts is dead. It may appear to recharge, but it will only come up in Voltage: significant Amp hour capacity will have been lost. This makes it even harder to stay ahead of use and self-discharge.

    Usage: looks like you've got about 1 Amp hour draw every ten days. (I might have mis-read or miscalculated.) So you could use a fairly small battery for this, with a small panel. Like this: http://www.solar-electric.com/unba35amseag.html with this http://www.solar-electric.com/spm040.html controlled with this http://www.solar-electric.com/sg-4.html

    Just an example: not a precisely calculated recommendation (especially if I goofed up the load figures!)
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: New Issue Question - Battery Not Charging

    i can now say i agree the battery would've sufficed as the pump could've run an hour or 2 from off of a fully charged battery and not be drained too far, as in not exceeding 50% dod. the problem then is definitely the pv being too small that it did not bring the battery up to full charge and the pump continued to drain what the battery had left in it. the battery may very well be ruined.
    if you wish to try again then by all means do so, but at a minimum you should have at least a 10w pv for an 8ah battery. 10w/14.4v=.694a. .649a/8ah=8.675% charge rate. now any losses as bill pointed out can pull that down lower than that for a good charge % and to be on the safe side a bigger pv could be used. a 10w pv could still work as a long term charger for the battery imo and i think it would be ok if those losses aren't real bad providing there be an occasional stronger charge given to the battery to insure the electrolyte is mixing well as smaller charges fall short of doing this.
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