Forum Discussion

Njmurvin's avatar
Njmurvin
Explorer
Sep 29, 2016

Batteries draining too fast after solar recharge

Last week I went dry camping. I could barely get through the night with my setup (single 100 watt solar panel, 2 12V group 24 deep cycle marine batteries) using lights (fluo) VERY sparingly and no furnace. Batteries were down to 50-60% by morning each day even though the solar controller (Go Power 30amp) reached float stage each day by mid-day.

I'm trying to diagnose where my deficiencies are (not enough panel watts, controller, batteries, etc.). So far I have removed one of the batteries to simplify my testing. Hydrometer says all cells are fully charged (well over 1.250). I have ordered a multimeter with amp clamp and I plan to determine what the overnight load is when the panel is not charging. Assuming refer on propane, water heater on propane and other parasitic stuff (CO and propane leak detectors) how much load is to be expected?

Dealer says the batteries should be 70ah each but they are off-brand cheapies that they installed. I am very suspicious that they're not providing anywhere close to 70ah. If they were, I would expect my solar system to be working much harder to replenish the batteries after getting down to 50-60% overnight.

Any suggestions for other tests?
  • harold1946's avatar
    harold1946
    Explorer
    Sep 30, 2016
    The first thing I would do is find out if the controller or solar panel/panels have a blocking diode. If not, that is where much of the battery is shedding power at night.
  • Njmurvin's avatar
    Njmurvin
    Explorer
    Sep 30, 2016
    Padlin wrote:
    Going into Float voltage (13.7), doesn't necessarily mean the batteries are fully charged. Would suggest you check the actual state of charge when it goes into float, or at some point shortly thereafter. I'd disconnect one of the battery cables and let it sit unused for a day. Then use your hydrometer.

    Another thought, try turning off all the loads in the trailer before you check for the State Of Charge as indicated by the GoPower. The GoPower converts the voltage level to the percentage you see, not all that accurate. If there is a load the voltage will be lower then it really is.

    The GoPower manual is pretty lousy.

    FWIW, I use about 10A a day depending on if I need the furnace.

    I couldn't agree more about the Go Power manual. And, I have spoken with their Tech Support guys several times and have even received conflicting information. The way I'm determining that it's in float stage is when the controller's outputted amps go down to less than 1 and there's still full sun. During charging, the Go Power voltage and SOC % readings are useless as it measures the voltage output of the controller, not the voltage of the battery. Only at night does it supposedly report battery SOC and, yes, other loads would affect those readings.

    Last night after sundown, I ran my bedroom slide in and out to make sure any surface charge was removed from my battery. I didn't let it sit for a day, but I did test again with the hydrometer and it was still reporting full. I should receive my amp meter today. I'll turn everything on to simulate dry camping (fridge, water heater, water pump, etc.) and measure current flow.
  • Padlin's avatar
    Padlin
    Explorer
    Sep 30, 2016
    Going into Float voltage (13.7), doesn't necessarily mean the batteries are fully charged. Would suggest you check the actual state of charge when it goes into float, or at some point shortly thereafter. I'd disconnect one of the battery cables and let it sit unused for a day. Then use your hydrometer.

    Another thought, try turning off all the loads in the trailer before you check for the State Of Charge as indicated by the GoPower. The GoPower converts the voltage level to the percentage you see, not all that accurate. If there is a load the voltage will be lower then it really is.

    The GoPower manual is pretty lousy.

    FWIW, I use about 10A a day depending on if I need the furnace.
  • Njmurvin's avatar
    Njmurvin
    Explorer
    Sep 29, 2016
    harold1946 wrote:
    Those batteries are not deep cycle, they are a hybrid deep cycle/starting battery. Not the best choice for your application. A true deep cycle is needed.
    At 70 AH each that gives a total of 140 AH and you need at least 140 watts of solar. Rule of thumb is 100 watts of solar for each 100 AH of storage.
    If the controller or solar panels do not have a blocking diode the batteries can discharge back through the panels at night.

    Understood that the batteries are not true deep cycle -but for the moment I would be delighted with 70ah usable. I agree that I'm probably a bit light on solar watts - even for 140ah total capacity. However, unless there is some phantom load pulling the batteries down, I can't see how my miserly power usage would have consumed 70ah overnight. And, if the panel/controller was simply too small to replenish the prior day's usage, I would have expected it to be in bulk charging mode (max amps) all day long. Instead, it thought it was done by mid-day and went into float mode.

    I've never heard of the blocking diode. I would assume that a Go Power controller would prevent the panel from drawing current at night. But, who knows? Hopefully, the clamping amp meter will help me understand where the power is going.
  • harold1946's avatar
    harold1946
    Explorer
    Sep 29, 2016
    Those batteries are not deep cycle, they are a hybrid deep cycle/starting battery. Not the best choice for your application. A true deep cycle is needed.
    At 70 AH each that gives a total of 140 AH and you need at least 140 watts of solar. Rule of thumb is 100 watts of solar for each 100 AH of storage.
    If the controller or solar panels do not have a blocking diode the batteries can discharge back through the panels at night.
  • Sam_Spade's avatar
    Sam_Spade
    Explorer
    Sep 29, 2016
    Njmurvin wrote:
    But I need to confirm that the overnight load is reasonable and that the solar can replenish what I use.


    Any propane appliance has a solenoid that uses power to open the propane feed while it is "ON". Or.....it shuts the gas off if the power goes dead. These can draw more than you might think.

    IIRC, some solar controllers can actually draw a small bit of power back out in the dead of night.

    The inability of a battery to give back what charge it has is one sign of wearing out......or being really cheap to start with.
  • korbe's avatar
    korbe
    Explorer
    Sep 29, 2016
    When we dry camp during the summer, with 90-percent of our day time spent outside, LED lights, frig on LPG, we use about 16 amps per 24 hours. Our 2 6volt batteries with 225ah will keep us going for up to a week - without solar or a nasty generator. My cheap volt meter was able to give me all that info which is "close enough" for me.
  • time2roll's avatar
    time2roll
    Nomad
    Sep 29, 2016
    Could be a battery issue however I would start by measuring the draw as your RV idles running the fridge etc.
    Should be less than one amp.

    Fridge humidity control is the first item to verify is off.
  • Njmurvin's avatar
    Njmurvin
    Explorer
    Sep 29, 2016
    laknox wrote:


    In my experience, a marine "deep cycle" (not =really= a deep cycle) battery should have at least 100 ah capacity. I know that my 2nd set of batteries were +/-110 ah each, for a total of 220 ah, when new. Check Costco or Sam's Club for their marine batteries and see what they have. 70 ah seems pretty anemic, to me.

    Lyle

    Agreed. If I determine it's the batteries that are malfunctioning, then Costco batteries will be front and center. But I need to confirm that the overnight load is reasonable and that the solar can replenish what I use.
  • laknox's avatar
    laknox
    Nomad
    Sep 29, 2016
    Njmurvin wrote:
    Last week I went dry camping. I could barely get through the night with my setup (single 100 watt solar panel, 2 12V group 24 deep cell marine batteries) using lights (fluo) VERY sparingly and no furnace. Batteries were down to 50-60% by morning each day even though the solar controller (Go Power 30amp) reached float stage each day by mid-day.

    I'm trying to diagnose where my deficiencies are (not enough panel watts, controller, batteries, etc.). So far I have removed one of the batteries to simplify my testing. Hydrometer says all cells are fully charged (well over 1.250). I have ordered a multimeter with amp clamp and I plan to determine what the overnight load is when the panel is not charging. Assuming refer on propane, water heater on propane and other parasitic stuff (CO and propane leak detectors) how much load is to be expected?

    Dealer says the batteries should be 70ah each but they are off-brand cheapies that they installed. I am very suspicious that they're not providing anywhere close to 70ah. If they were, I would expect my solar system to be working much harder to replenish the batteries after getting down to 50-60% overnight.

    Any suggestions for other tests?


    In my experience, a marine "deep cycle" (not =really= a deep cycle) battery should have at least 100 ah capacity. I know that my 2nd set of batteries were +/-110 ah each, for a total of 220 ah, when new. Check Costco or Sam's Club for their marine batteries and see what they have. 70 ah seems pretty anemic, to me.

    Lyle

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