Help! Batteries draining right away

wwkdshoot

Hi! I just installed a solar system on my truck camper. My goal was to be able to use my 1500w heater for the night. First attempt got me 6 hours before fully depleted. Since that - it took almost 7 days to fully charge the system (full sun- desert). Now the batteries deplete within an minutes!  Any help / insights super appreciated! Here’s the system: 
Renogy 2 x 100w panels wired in series to ‘Adventurer’ controller (kit) wired to 4 x 1000A AGM sealed batteries (wired in parallel) to 3000W inverter. 
Have tested system with smaller heater/ fan and watched it deplete from 100% to 60% within minutes. Seems to be charging back up ok now, - sunny day already back to 98%. 

I just ordered a battery tester - any other ideas??

MichaelK

Grossly imbalanced system.  Simple math points to why it is failing.  You are running a 1500W heater for perhaps 10h per night?  That works out to be 1500W X 10h = 15000Wh.  You have four 100Ah batteries at 12V.  That works out to be 4 X 100 X 12V = 4800Wh of power.  You are trying to pull 15000Wh of power out of a battery bank that can only hold <5000Wh.

You are trying to charge this poor battery with 200W of solar.  You have it connected to a PMW controller, so you're 200W is actually only 140W.  Assuming you have 4 sun hours per day right now, you're making 140W X 4 Sh= 560Wh per day.  So, you are trying to replace 4800Wh with panels only producing 560Wh per day.

Add another 4 12V panels, or at least 2-3 250W grid-tie panels.  Also get a MPPT controller to replace the PMW.  You'll need one that can handle 40+ amps.  To get those batteries fully charged, even this much enhanced system will still take you two days to charge that much.  What you need is a maximal charging rate, (30amps), so your math is 30Ah X 13V charging X 1.25 loss factor = 488W.

In the mean time, pull those batteries out and get them charged 1 by 1 on a tabletop 12V charger.  Leaving them in such a depleted state for very long will result in permanent sulfination, and diminished total capacity.  After they get hooked back up, never draw them down further than 50% capacity.  Otherwise you will very quickly destroy them.

Photowhit

You have 200 watts of array, I have 5000 watts of array and would NOT consider running a 1500 watt heater.

Heating and cooling aren't things solar does well. If you wanted to try to do a 'little' heating to make camping easier try a mattress heater on timer for hour or so to help get to sleep. It draws 1/3rd of a electric blanket. 

The 'math is ugly trying to heat. Watts=amps x volts. 1500 watts from a 12 volt system is 1500watts/12 volts=125 amps per hour.

706jim

1500 watt heater on your system = dead batteries.

MichaelK

Sorry, but I saw an math error in my previous post.  I forgot to account for the fact that you have four of those batteries in parallel, so the current load must be 4X higher.  So, instead of 30Ah X 13V charging X 1.25 loss factor = 488W,  the correct math would be....

30Ah X 4 parallel strings X 13V charging X 1.25 loss factor = 1950W.  I guess that's not very realistic on a camper roof.  But, even at 1/10C the math would still be...

10Ah X 4 parallel strings X 13V charging X 1.25 loss factor = 650W.

Can you get three grid-tie panels on top of your roof? Say, three 240W panels?  You'll need a controller that can handle 50+amps.  Your practical choices are either add more solar, and a better higher-capacity MPPT controller, or reduce your battery bank to a size that would give you at least a 1/10C charging rate?

(200W solar/13V charging) X .80X loss factor x 10 fold battery capacity = ~123Ah.  Call it a 120Ah battery.

wwkdshoot

Ok thank you for your advice, I tested the batteries and they are coming out at 80% (from battery tester - so they should still be ok) 
I think you are right that there is not enough power in the 200w panels to recharge them. However, my big issue seems to be that the batteries drain almost immediately- I watched them drop from 100% to 70% within 30 seconds with a hot water kettle (on low, so around 200v). I have ordered a battery charger to charge each to 100% individually to see if that helps with the discharge. 

I’d be willing to lose some batteries to get the system to fully charge / work. I could also get bigger wattage solar panels for the roof, the footprint is the same... just hate to have to ditch what I have already. There’s no room on the roof for additional panels, so having panels to prop outside the truck / flexible could work? 

If I can’t get my current batteries to work, could you recommend some that would work with the panels I have? 

Photowhit

wwkdshoot said:

I think you are right that there is not enough power in the 200w panels to recharge them. However, my big issue seems to be that the batteries drain almost immediately- I watched them drop from 100% to 70% within 30 seconds with a hot water kettle (on low, so around 200v). 

What are you reading when you "...them drop from 100% to 70% within 30 seconds..." 

I suspect you are reading a voltage based battery monitor. Those are right about twice a day in an active system.

When charging they will read a higher system voltage than a resting battery voltage. When discharging, they will read a lower system voltage than a resting battery voltage. Only if your system is resting with no charging or loads for a couple hours will you get a somewhat correct idea.

Want to test my information? Perhaps you already did... If you removed the kettle after 30 seconds, did the % of capacity go back up after a little bit?

I doubt a kettle on low is 200 watts, you might check that... Though it is possible, I have a 200 watt rice cooker, though it's better insulated than most and only make up to 3 cups of rice at a time.

It's certainly possible that the batteries have lost capacity during there time of being chronically undercharged...

There are shunt based battery monitors. Starting around $200 with a shunt, but I've always felt that if you will learn the rise and fall of battery voltage it will serve you better.

BB.

If you are living in the van full time (vs weekend usage)--The typical starting point for system design is 2 days of storage and 50% discharge... And at least 10% to 13% rate of charge.

Regarding panels--If you have "crystalline" type panels--There is probably no reason to change them out for a "better" panel (you may get 10-20% more harvest--Not much).

One thing that can increase harvest a lot--Especially in winter... Here is the amount of sun you can collect in Austin Texas, with an array mounted flat to roof (i.e., fixed roof mount on van), vs tilting to 45 degrees from vertical (tilt to collect more winter sun):
http://www.solarelectricityhandbook.com/solar-irradiance.html

First flat to roof:

Austin
Average Solar Insolation figures

Measured in kWh/m2/day onto a horizontal surface:

Jan	Feb	Mar	Apr	May	Jun
2.83	3.41	4.40	5.25	5.62	6.36
Jul	Aug	Sep	Oct	Nov	Dec
6.56	5.94	4.97	4.05	3.07	2.63

And then tilted to 45 Degrees for Winter Harvest:

Austin
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 45° angle:
(Optimal winter settings)

Jan	Feb	Mar	Apr	May	Jun
4.03	4.25	4.74	4.89	4.61	4.88
Jul	Aug	Sep	Oct	Nov	Dec
5.12	5.18	5.08	4.90	4.25	3.91

And best year round average harvest:

Austin
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 60° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
3.82	4.18	4.86	5.27	5.19	5.65
Jul	Aug	Sep	Oct	Nov	Dec
5.90	5.72	5.31	4.87	4.07	3.67

In general, you can probably collect more winter harvest if you can tilt your array to south than getting more efficient panels (2.83 hours of sun January flat; 4.03 hours of sun for January at 45 degrees)...

Lets say you can tilt the array to 60 degrees from vertical (or 30 degrees from horizontal) and look at January:

• 2.83 hours of sun per day (Jan flat) * 0.52 off grid AC system eff * 200 Watt array = 294 WH per Jan @ flat day
• 3.82 hours of sun per day (Jan @ 60 degrees) * 0.52 off grid AC system eff * 200 Watt array = 397 WH per Jan @ 60d Vert

For a full time off grid system--Suggest that the battery bank support 2 days of power usage (2 days of bad weather) and 50% max planned discharge (for longer battery bank/emergency reserve):

• 397 WH per day * 1/0.85 AC inverter eff * 2 days storage * 0.50 max discharge * 1/12 volt battery bank = 156 AH @ 12 volts "suggested" battery size (based on winter production)

Of course, if you have alternative charging (van alternator, backup genset, shore power, just use less power in winter)... You can support a larger battery bank/more charging energy.

Anyway--Suggest 5% to 13%+ rate of charge for solar... And 10%+ for full time off grid charging. A 200 Watt array will support (solar only charging):

• 200 Watts * 1/14.5 volts charging * 0.77 panel+controller derate * 1/0.05 rate of charge = 212 AH battery @ 12 volts "max"
• 200 Watts * 1/14.5 volts charging * 0.77 panel+controller derate * 1/0.10 rate of charge = 106 AH battery @ 12 volts "nominal"
• 200 Watts * 1/14.5 volts charging * 0.77 panel+controller derate * 1/0.13 rate of charge = 82 AH battery @ 12 volts "minimum

Roughly, I would be suggesting around a 106 to 156 AH @ 12 volt battery bank with a tilting 200 Watt solar array (and no other source of charging).

Things you can do to add solar charging? Making a tilting "array" for the side of the van (fold down to side of van, or fold over roof (and existing panels to store for travel)... Put it on the driver's side (avoid side doors), or on the passenger side if you want an awning over the side door (rain/sun):

You have to figure out what the amount of energy per day you really need (most energy efficient loads you can find--I.e., tablet computer or vs small laptop vs full desktop computer), RV water pump, LED lighting, etc...

For heating--Just to give you an idea... a 1,500 Watt system with 397 WH per day (Jan tilted array):

• 397 WH per day (Jan/tilt) 1/ 1,500 Watt inverter = 0.26 hours = 15 minutes per day

If you got a diesel fuel heater (popular for vans), 1 gallon of diesel will give you the equivalent:
https://www.convertunits.com/from/gallon+[U.S.]+of+diesel+oil/to/kilowatt+hour

• 1 gallon of diesel = 40,700 WH of energy
• 40,700 WH * 0.85 heater eff = 34,595 WH of "heat"
• 34,595 WH of heat / 1,500 Watt electric heater = 23 hours of "electric heat" equivalent (on 100% of time)

Genset wise... Get a small Honda eu1000i or equivalent genset (gasoline) for backup charging/power:
https://powerequipment.honda.com/generators/models/eu1000i

• 900 Watts full output * 0.25 output (example 225 Watt load) * 6.8 hours (at 25% load) / 0.55 gallon tank = 2,782 WH per gallon of fuel
• 2,782 WH per gallon / 397 WH per day Jan/tilt harvest per day = 7 days of "winter solar equivalent" per gallon of gasoline

A small genset and a few gallons of gasoline is not the worst solution if you need more electricity than your solar system can supply (use genset to recharge battery bank and/or directly support your larger AC loads when needed).

We are talking a lot about loads... And you need something to measure them. Some examples:
https://www.amazon.com/s?k=kill-a-watt&ref=nb_sb_noss (Kill-a-Watt type meters for 120 VAC plug in appliances)
https://www.amazon.com/s?k=dc+watthour+amphour+meters&ref=nb_sb_noss (DC WH/AH meters)
https://www.amazon.com/UNI-T-UT210E-Capacitance-Multimeter-Resolution/dp/B075ZHDQFP ("good enough" AC/DC current/DMM meter)
https://www.amazon.com/gp/product/B019CY4FB4 ("better" AC/DC current/DMM meter)

The above are just suggestions... You can look through them and see what may work better for your needs. And there are lots of other options (Battery Monitor Systems) that are nice too.

I threw a lot at you... It really comes down how much electrical energy you need--And what it is worth to you (something nice/to keep you sane--Or need to make money at a remote job site). The system needs to meet your needs and expectations.

-Bill