Keeping batteries in check - two ideas.

Hello all.

I'm trying to keep my batteries in top shape by not allowing them to discharge too deeply. I'm in Ohio, so sun is iffy on many days and the gloomy, cloudy days of fall are starting. Although we do have some good streaks of sunny days as well.

I still have grid and this is mainly a hobby and educational experience.

My bank is 225aH, 24VDC. I usually discharge about 10-20% each night combined from the following; running some lights, vampire loads (ie; wall warts), TV, minimal Trimetric draw, etc.

My thoughts are that I could run autonomously for 2-3 days before a recharge is *really* needed and my hopes are (ideally) that I will have a good sunny day while I'm at work to recharge my batteries within those 3 days, thus keeping me off grid for the said circuits in my house. I'm at work 8-9 hours/day 5 days a week. Theory is great, huh?

If the coulds have the nerve to stay over my house for 2-4 days, I was thinking...

I don't have a generator, but I do have an IOTA DLS 27-25/IQ4 24VDC 3 stage charger that I purchased from a member here. The built in setpoints for bulk, absorb, and float are slightly under what my Trojan t105re's need. This IOTA has a function where it senses the voltage of the battery bank and if it's under 25.6V, the charger will initiate it's charging process. (Specs can be found here --> At first thought, I was thinking that I'd always keep the charger on the grid thus monitoring the bank, but I quickly realized that the bank will fall below the sense voltage of 25.6V if I turn on a small load for a brief period of time. This seems counterproductive to me; if I use a load, the charger quickly turns on I pay for the grid to energize my charger every time a load is used. In fact, because of the stages the charger cycles though and inefficiencies involved, I'd actually pay more to use that load than directly using the grid.

So, I thought, "If I could turn the IOTA on... say... every 2.5 days and 'peek' at the bank that would suffice". I scrounged around my shed and found a timer that I can preset values into. I also found a 24VDC relay with 120VAC secondaries. I could make this work! I preset some values and connected it to the relay and everything is functioning fine. I have not yet wired it to the IOTA charger.

I'm looking for feedback, criticism, advice, etc. What do you think about having the charger peek at the bank every 2.5 days? 2.5 days is an arbitrary value that I feel safe based on my usage. I can program the timer to keep the secondaires pulled in for 8 hours which is the amount of time the IOTA needs to perform it's entire charging process.



  • rgk1rgk1 Solar Expert Posts: 107 ✭✭✭
    Re: Keeping batteries in check - two ideas.

    I have a similar situation, hobby and educational system. I just run a shed light on a photocell for dusk to dawn lighting, charge battery packs, interior shed lights, recharge battery packs, and a radio. I too have an Iota charger for cloudy stretches or if there is an outage and I run the batteries down with tv, sattelite, etc. I my memory is correct, assuming you leave the charger connected to the battery all the time, it will keep tabs on voltage...even if the power cord is unplugged. If it has at any time since the last time it was plugged in detected voltage between setpoints, it will start charging in the appropriate mode. I have the + side of mine on a breaker. I keep it unplugged and the breaker off. If I plug it in and turn the breaker on, it detects the here and now battery voltage and goes into charge or float based on that voltage. I do keep a generator just in case though.
    4-Kyocera 135 watt in series, 4-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/24 volt inverter, Tristar 45 MPPT controller, Iota 24 volt/25 amp charger.
  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Keeping batteries in check - two ideas.

    I'v had the same situation on my boat for 30 years. Parasitic loads will throw any 3 stage charger into the absorption phase and keep it locked there, on a 2 stage it's worse, it will go to bulk. On a 12 v system it's 14.0 + / - and 24/7 will cook a battery till it dies.

    I have a old Exide battery charger ( PWM controller ) that had pots on the controller boards and I have them adjusted to give me a 13.2 V , output. The lower voltage seems to keep the battery happy and will still supply what I need for the loads that can be between 1 amp and 10 amps.

    Smart chargers are not all that smart, they may have a time limit on the absorption phase, but with a constant load, they just reset and start the cycle over and over.

    I have a IOTA IQ4 that I will manually let run through it's full cycle every couple weeks on those house batteries.
  • drew4justicedrew4justice Solar Expert Posts: 36
    Re: Keeping batteries in check - two ideas.

    Here is my idea in motion. Sorry about the rambling on...
  • RandomJoeRandomJoe Solar Expert Posts: 472 ✭✭✭
    Re: Keeping batteries in check - two ideas.

    If you get something that will track amp-hours in/out (Trimetric, Xantrex has a little meter as well) or perhaps you could configure the device you have to do it, then you could just have a relay switch the inverter on if AH-out gets too high - say when you drop below 70% SOC.

    That's more or less what I do with my system, although I "cheated" a bit and bought an Outback system rather than homebrew. The Outback power monitor tracks battery bank status, and my home automation panel has a bit of logic in it to determine when to allow grid use and/or battery charging.

    Unfortunately, my desired loads - though small, they are continuous - are enough that 24x7 operation cycles my bank more than I care to each day. So my logic also watches for when the system goes to sleep at night, and moves back to grid (but not charging). At some point in the wee hours of the morning it will switch back to battery to give the solar panels something to do once the sun comes up! :)

    I have this Grand Scheme in my head for something a lot more flexible / involved, but haven't found A Round Tuit yet... :p One of these days... (Of course I'd also like to expand the system - caught myself looking at solar panels at the NAWS store again last night! :cool: )
  • drew4justicedrew4justice Solar Expert Posts: 36
    Re: Keeping batteries in check - two ideas.

    Thanks Joe. I do have a Trimetric controller and it does contain a serial connection, but I can't find software to perform this function. Maybe I'll work on a system to interface/monitor and throw the relay at -30 aH out or something of the like.... I haven't had any experience with a PIC microcontroller, basic stamp, or similar but it just might be an excuse to experiment.
Sign In or Register to comment.