off grid in the jungle

So a friend of mine who lives in the jungle is having some concerns about his system. I went in to help him because I am more familiar with electrical work.

1400 watts of panels in 5 48V strings
an outback MX80 MPPT Charge controller
6 220AH East Penn 12V Gel batteries in parallel.
outback FX 200 inverter
outback mate

the concern is with maximum charge current. following the C/20 rule we are looking at 66A max, so I set the charge current at 66A max. Everything worked great until he started running appliances while charging. With 30A coming out of the batteries to feed appliances, only 36A was charging the batteries.

I thought, ahh, I must have forgotten to install a current monitoring shunt to let the mate know that some of the power it is feeding the batteries is being diverted to the appliance fuse-box. I re-read the Flex Max instructions and did not see any reference to a shunt. I re-read the FX manual too, and didn't see anything.

What am I missing, I want to set it up so that It will account for power flowing out of the batteries into the appliances and deliver that much power in addition to the 66A current limit. At least up to the 80A that the FM80 can handle.

I guess I will re-read the mate instructions.


  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: off grid in the jungle

    Six 12 volt batteries in parallel? Ouch, gonna be hard to keep them all in an equal state of charge. And gel type? No room for error whatever.
    I wish you luck.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: off grid in the jungle

    Welcome to the forum.

    Where shall we start with what is wrong? There's lots.
    First of all, gel batteries are not good for RE use. They can't take the cycling and are very Voltage and current particular.
    Second, six 220 Amp hour batteries in parallel is not only a problem for keeping current flow balanced, but it's also 1320 Amp hours of battery. This is really large for a 12 Volt system and bound to suffer problems.
    As far as I know, there is no shunt to be wired to the MATE, FM80, or FX2012. None of these devices are battery monitors and they can not keep track of current flowing in and out of the batteries. Their functions are Voltage dependent.

    30 Amps being diverted for appliance use should not be a problem, as long a it is not continuous (all-day resulting in chronic deficit charging). It's only 360 Watts. The big trouble here would appear to be the unsuitable batteries. The gels aren't good at delivering current, and the wiring configuration is likely causing some to be drawn on more than others. These batteries should be wired with equal-length cables to positive and negative bus bars, and the inverter & charger attached to them. That is the best way to keep the current flowing evenly.

    If you must use gel batteries you really do need a battery monitor as there is no other way to tell the state of charge of the battery. Chances are they are ruined already, and should be replaced with FLA's or AGM's. Before doing that, re-asses the power needs because 1320 Amp hours @ 12 Volts is nearly 8 kW hours of power potential and it's doubtful that much is actually needed.
  • BB.BB. Super Moderators, Administrators Posts: 32,027 admin
    Re: off grid in the jungle

    I don't know anything about the Mate... But I would suggest sending him a DC Current Clamp Meter (something like this for $60 should work well for debugging). Can measure the currents in the system/panels to confirm operation and monitor the paralleled battery bank to ensure that the batteries are properly sharing current (charging/discharging).

    I don't know of any system that limits charging current to battery using load current as part of the equation.

    In any case, charging voltage set point of 13.8 to 14.1 volts is critical for GEL (using the East Penn information--PDF). This is a relatively low charging voltage for lead acid batteries, so should keep charging current lower. Also, does he have a remote temperature sensor connected to the battery bank and the Outback charging controller?

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: off grid in the jungle


    Thanks for the replies, there seems to be a wealth of knowledge here for a rather complex subject, so I appreciate the help.

    He is running 12V because the majority of his house uses DC 12V appliances.

    He has 1320AH because there are many tropical storms which block charging and he wants the extra charge to get him through those days. If a single rainy day is 16 hours of 250W average consumption with no charging, that makes 4kWh or 50% SOC. Petrol is very expensive to get into his location, so he was adamant about needing a large storage capacity.

    I agree that gells are not the best option for this system, and I wish he had LEs. We already discussed the fragile nature of his batteries and how replacing them with something else when these fail will be something to plan on.

    They live in the house, so the diverted load feeding appliances will vary widely depending on what appliances they are using. Computers and fans will be relatively continuous, but AC loads for washing cloths and working in the kitchen will be intermittent. I would estimate 15-20A as their average diverted load during charging hours, but it would range form 0A to 120A. It will be a significant factor, so I agree with you that the SOC monitor will be necessary.

    I did some further research and outback makes a device called the Flexnet, which I think would be what he needs, it monitors charge from the inverter, charge from the CC, and draw from loads, so that the mate can display SOC and coordinate the two charging devices. With all the necessary shunts, the thing ends up selling for around 450$ which seems awfully expensive, but maybe worth it if it he gets more time out of the batteries, and keeps everything made by Outback for homogeneity.

    So if I can get him set up with the Flexnet and he switches out to LEs on equal length wires, is there anything else that should be done?

  • System2System2 Posts: 6,290 admin
    Re: off grid in the jungle


    He does have a temperature sensor on the batteries and the chargers are programmed with the voltage settings recommended by East Penn.

    He does not have a current clamp, but I could recommend that he pick one up, They had to go home to Taiwan for medical reasons and it does not look like they will be back for a while.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: off grid in the jungle

    Here's a suggestion you might want to think about: divide the system in two.
    There could be one "DC only" system sized to handle the DC appliances, and a second "AC supply" system tailored to meet the needs of the AC powered devices. Preferably the AC system would be 24 Volt, which could better handle loads like washing machines and refrigerators. But since that would entail buying another inverter and controller it probably wouldn't be popular with the guy whose money is being spent. Even so, dividing in to two 12 Volt systems would ease the current requirements for charging and keep the heavy loads from causing brown-outs on the lower power set-up.

    Any way you figure it the system needs new batteries, more panels, and a second controller.
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