I’ve often laughed at myself realizing that solar power for camping has taken me all the way back to the fifties and listening to DC Ohm’s law the first time. Maintaining industrial UPS back-up systems and my own golf cart’s batteries kept me sort of in tune over the decades. Below is my experience, and learning from my own mistakes, probably including some below.
The parasitic drain on modern vehicles can exceed 100mA (.1A) DC, especially if aftermarket things have been connected. That can lower the battery voltage to less than 12.6 rather quickly. Any device that provides a readout or has memory is powered from something.
An accurate DC clamp-on meter can help determine that. Many, many vehicles start regularly with lower than 12.6V. Few vehicles have factory digital voltmeters.
The specific gravity tester is very important.
An accurate down to low amps DC clip-on ammeter is as valuable for determining flow (amps), as the voltmeter is for pressure (volts). I feel it is a must have. Clip around a battery lead or any current carrying wire. Over time, as you learn what to expect for solar output amps, a lower reading will alert you to voltage losses/resistances somewhere.
The battery will restrict amp flow into itself as the voltage rises to full charge. Usually no more than one or two amps at nearly full charge. That can be read with a clip on dc ammeter. If the current remains higher over a long period of time, especially when compared to a like battery on a dual system, possible battery problem. Also, undue alternator load. Refer back to specific gravity testing.
Any mechanical connection is suspect for a power loss (pressure/voltage drop) as measured with a DC voltmeter. That includes contact nastiness/corrosion on a solenoid/relay’s internal contacts. That voltage drop/loss is best measured during maximum current flow, in this case, when charging a run-down or faulty battery with the alternator. My starter/house battery solenoid has a .2vdc drop/loss across the contacts at about a 30 amp charge rate. Six watts wasted. Charging voltage at the house battery is .2vdc less than the starting battery/alternator voltage during initial charging due to that solenoid. As the house battery charges, current through the solenoid contacts decreases, along with its voltage loss across the contacts until finally, the battery voltages become equal. It takes a LOT of driving to do that. I let solar top it off.
The sharp pointed ends of a voltmeter’s test leads can pierce most wire insulation to allow contact to the wire if need be. Piercing the wire near the terminal and the other wire on a battery post should read almost zero volts during heavy charging.
For your solenoid, energized while trying to charge a depleted battery, the DC volts measured with one test lead on each top solenoid post should also read close to zero across the closed contacts. Any voltage measured, even tenths, will subtract from the charging sources output voltage. That reduced voltage will be measured at the other battery.
On either battery, any voltage measured from the wire to the post reduces the charging voltage by that amount. Same for terminal strips or any other mechanical connection. With long enough test leads, one lead on each battery’s positive post (not terminals, but actual posts) will show total voltage loss in that line and any connections between batteries. If you can also measure amps, multiply amps times the hopefully small fraction of a volt to get loss in watts.
I have 25’ long meter test leads made from extremely small wire to measure voltage drops along a single wire from solar panel to charge controller. A long run of seemingly large enough charging wire, even with no connections, just wire, will show a small voltage drop as current (amps) increases. Connections can make it worse.
I have seen different operations for the starter/house battery solenoid. Some energize(close) only in the RUN keyswitch position. Some are energized in either RUN or START.
START allows the batteries to be joined together to aid in starting. That can be good or bad. If you’ve ever tried to jumpstart a vehicle with a dead battery, the dead battery can place enough load that no rah rah rah cranking happens until you wait a while for the dead battery to rise somewhat, or disconnect the dead one to remove its load from the good battery. Also, connecting the batteries during START can mask a low individual battery.
I have three Renogy Viewstar PWM controllers. They provide solar voltage, battery voltage, and current (amps) as a digital readout. Very handy as mentioned by others and to me, quite necessary.
I also use really cheap Chinese PWM controllers that provide those same parameters. Push a button to read panel voltage, battery voltage, and charging current. My cheapos can be programmed to output up to 15vdc and sit there. No timed equalization. 14.6 or higher works for me. They work just fine for flooded batteries if you keep check on liquid level and specific gravity. Exposed plates should disappear quickly due to shedding excess tears. Replacing batteries wasn’t so bad when someone else paid for them.
My starting battery, since new, will drop to the low twelves in about four days when it receives no charging. I often have excess solar power due to a fully charged house battery. My solution to the starter battery drain was to run a wire from the house battery side of the solenoid through a 150 amp manual switch, to the positive side of the starting battery.
Turning on the switch keeps both batteries charged from solar when needed. Another bonus is if the start battery is a little low to rah rah rah fast enough or not at all, you can turn on the switch for a while to give the starter battery a boost, then turn the switch back off. That wire doesn't have to be battery cable large. As small as 6 gauge can handle short bursts of starter or charging current. Exercise caution.
Totally conjecture and no proof: I have gotten pairs of the highest specific gravity 6v golf cart batteries being replaced by owners for the return core charge. My smart charger nor my dumb charger could raise the specific gravity, but a PWM solar controller could. I think it’s the pulses. Pure speculation.
Good luck from another keep it cheap believer. I've been through basically the same steps.
The parasitic drain on modern vehicles can exceed 100mA (.1A) DC, especially if aftermarket things have been connected. That can lower the battery voltage to less than 12.6 rather quickly. Any device that provides a readout or has memory is powered from something.
An accurate DC clamp-on meter can help determine that. Many, many vehicles start regularly with lower than 12.6V. Few vehicles have factory digital voltmeters.
The specific gravity tester is very important.
An accurate down to low amps DC clip-on ammeter is as valuable for determining flow (amps), as the voltmeter is for pressure (volts). I feel it is a must have. Clip around a battery lead or any current carrying wire. Over time, as you learn what to expect for solar output amps, a lower reading will alert you to voltage losses/resistances somewhere.
The battery will restrict amp flow into itself as the voltage rises to full charge. Usually no more than one or two amps at nearly full charge. That can be read with a clip on dc ammeter. If the current remains higher over a long period of time, especially when compared to a like battery on a dual system, possible battery problem. Also, undue alternator load. Refer back to specific gravity testing.
Any mechanical connection is suspect for a power loss (pressure/voltage drop) as measured with a DC voltmeter. That includes contact nastiness/corrosion on a solenoid/relay’s internal contacts. That voltage drop/loss is best measured during maximum current flow, in this case, when charging a run-down or faulty battery with the alternator. My starter/house battery solenoid has a .2vdc drop/loss across the contacts at about a 30 amp charge rate. Six watts wasted. Charging voltage at the house battery is .2vdc less than the starting battery/alternator voltage during initial charging due to that solenoid. As the house battery charges, current through the solenoid contacts decreases, along with its voltage loss across the contacts until finally, the battery voltages become equal. It takes a LOT of driving to do that. I let solar top it off.
The sharp pointed ends of a voltmeter’s test leads can pierce most wire insulation to allow contact to the wire if need be. Piercing the wire near the terminal and the other wire on a battery post should read almost zero volts during heavy charging.
For your solenoid, energized while trying to charge a depleted battery, the DC volts measured with one test lead on each top solenoid post should also read close to zero across the closed contacts. Any voltage measured, even tenths, will subtract from the charging sources output voltage. That reduced voltage will be measured at the other battery.
On either battery, any voltage measured from the wire to the post reduces the charging voltage by that amount. Same for terminal strips or any other mechanical connection. With long enough test leads, one lead on each battery’s positive post (not terminals, but actual posts) will show total voltage loss in that line and any connections between batteries. If you can also measure amps, multiply amps times the hopefully small fraction of a volt to get loss in watts.
I have 25’ long meter test leads made from extremely small wire to measure voltage drops along a single wire from solar panel to charge controller. A long run of seemingly large enough charging wire, even with no connections, just wire, will show a small voltage drop as current (amps) increases. Connections can make it worse.
I have seen different operations for the starter/house battery solenoid. Some energize(close) only in the RUN keyswitch position. Some are energized in either RUN or START.
START allows the batteries to be joined together to aid in starting. That can be good or bad. If you’ve ever tried to jumpstart a vehicle with a dead battery, the dead battery can place enough load that no rah rah rah cranking happens until you wait a while for the dead battery to rise somewhat, or disconnect the dead one to remove its load from the good battery. Also, connecting the batteries during START can mask a low individual battery.
I have three Renogy Viewstar PWM controllers. They provide solar voltage, battery voltage, and current (amps) as a digital readout. Very handy as mentioned by others and to me, quite necessary.
I also use really cheap Chinese PWM controllers that provide those same parameters. Push a button to read panel voltage, battery voltage, and charging current. My cheapos can be programmed to output up to 15vdc and sit there. No timed equalization. 14.6 or higher works for me. They work just fine for flooded batteries if you keep check on liquid level and specific gravity. Exposed plates should disappear quickly due to shedding excess tears. Replacing batteries wasn’t so bad when someone else paid for them.
My starting battery, since new, will drop to the low twelves in about four days when it receives no charging. I often have excess solar power due to a fully charged house battery. My solution to the starter battery drain was to run a wire from the house battery side of the solenoid through a 150 amp manual switch, to the positive side of the starting battery.
Turning on the switch keeps both batteries charged from solar when needed. Another bonus is if the start battery is a little low to rah rah rah fast enough or not at all, you can turn on the switch for a while to give the starter battery a boost, then turn the switch back off. That wire doesn't have to be battery cable large. As small as 6 gauge can handle short bursts of starter or charging current. Exercise caution.
Totally conjecture and no proof: I have gotten pairs of the highest specific gravity 6v golf cart batteries being replaced by owners for the return core charge. My smart charger nor my dumb charger could raise the specific gravity, but a PWM solar controller could. I think it’s the pulses. Pure speculation.
Good luck from another keep it cheap believer. I've been through basically the same steps.
