Powering my house from my mower

GaryGary
GaryGary Registered Users Posts: 9
Hi,
I've picked up an ElecTrak electric garden tractor: http://www.myelec-traks.com/E16.html -- it has a battery pack consisting of 6 golf cart batteries -- Trojan T105's in my case. It was built in 1980, and is in need of a "bit" of work, which I'm in the middle of.

Anyway, I'd like to:
1. Use the battery pack to power a few bare minimum loads in my house in case of a long power outage.
and,
2. Recharge the battery pack during power outage emergencies from my existing grid-tied PV rig:http://www.builditsolar.com/Projects/PV/EnphasePV/Main.htm

The plan is to temporarily recable up about 6 of my 215 watt PV modules into two strings that would go to a regular charge controller, which would charge the batteries as on off-grid system. This may seem a bit extreme, but it looks to me like its only disconnecting and reconnecting 6 pairs of the MC4 connectors -- maybe a 15 minute job -- especially given that its a ground mount system with all the connectors very accessible.
This would be paired with an inverter that was just big enough to handle the minimal house loads. The minimal house loads would just be connected to the inverter with extension cords -- no breaker box changes.

The advantage I see in this approach is that effectively I get a battery backup grid-tied system without the expense of buying and maintaining a dedicated battery pack for it that almost never gets used.

The problem I'm running into is that the battery pack is wired as a 36 VDC series connection of the 6 batteries. There does not appear to be much equipment out there for 36 VDC battery packs.

On the inverter, after a lot of looking, I bit the bullet and paid $800 for the 3600 watt TrippLite 36 volt inverter even though its much larger than what I need. This is somewhat justified in that I need a charger that will charge from AC mains for normal operation, and the TrippLite also functions as a good charger from AC power -- I guess its intended for UPS systems that need inverter and charger.

The other thing I need is a charge controller, and again it seems hard to find a charge controller for 36 volt packs. The only ones I've found are the pretty expensive and oversize Outback FX60 unit and the Xantrex 150 model. Both of these look like they would do the job, but they are bigger than I need and on the pricey side for something to be used only in emergencies.

Is anyone aware of a smaller and less expensive charger controller that will do a 36 volt pack? Or, some other alternative?


Gary

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Powering my house from my mower

    Sounds viable. Looks like you've done the right calculations (six of the 215's work out to about the right size array for 36 Volts of 225 Amp hour battery).

    But you're probably going to have to go for an MPPT controller unless those panels are 12 Volt nominal. You're looking for an Absorb Voltage around 44.4, and an array Vmp of 53 - 54.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Powering my house from my mower

    Yes, you are correct... 36 VDC is virtually non-existent with standard solar PV systems, trucks, or other vehicles. You might find some 36 VDC UPS systems (Tripplite, etc.). And Outback has a 32 VDC inverter (perhaps you can configure for 36 without too much trouble).

    About the only common 36 vdc system seem to be (older?) boats... So, you may end up having to buy expensive hardware (charge controllers, inverters, etc.) to use your batteries for "free" backup.

    You might also check the MorningStar TS MPPT controller series and the Midnite solar Classic charge controllers too... They may support 36 VDC battery banks (MorningStar probably needs an optional computer interface/converter).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: Powering my house from my mower

    Looking at the problem now, you have 2 loads that are 36 volts, so it makes sense to looks for a 36 volt charge controller, but before you bought the inverter, it might have made sense to charge the batteries at 12 volts, and use them at 36 since you would only need the 36 volts when mowing, the inverter and charging system could both work at the same time.

    You could do this with a an plug of sorts so that when plugged into the inverter/solar the batteries where in series and parallel to make 12 volt bank and when used as a lawn mower, you'd plug in a connector to make the all one series. You might do this with a couple 110 dryer plugs and outlets, I think they handle 8 gauge wiring, might be heavy enough for the tractor.

    I did this sorta thing while on a bicycle trip, charging a couple SLA 6 v batteries at 12v and using them at 6 volts, Of course I was using maybe 6 amp batteries and wasn't likely to do any harm...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • rollandelliott
    rollandelliott Solar Expert Posts: 834 ✭✭
    Re: Powering my house from my mower

    Wow I didn't know electric tractors exsisted!
    Just curious
    http://www.coppergreen.com/coppergreen.htm
    does this stuff work well. I noticed you used it on your PV array.
  • RandomJoe
    RandomJoe Solar Expert Posts: 472 ✭✭✭
    Re: Powering my house from my mower

    Outback's FlexMax 80 and the Midnite Solar Classic charge controllers will both work with a 36V battery bank so no problem connecting the panels for charging. And if you decide to do something different later, they'll work just fine with almost any other bank voltage too so no money lost there.

    Just looked at the specs for Outback's 32V inverter/charger - it's in the "mobile" category, looks like it's intended for marine use. The voltage range is okay - says 28.0-45.3V DC - so should be useful as long as the charge settings and cutoff voltages can be adjusted. (I would guess - but don't know - that these are basically the same as the regular FX/VFX models where just about anything is adjustable...) However, all inverters I've ever seen are fixed input voltage, so if you pick up a really oddball voltage inverter you're out that money should you decide to change to a more common setup.
  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: Powering my house from my mower
    BB. wrote: »

    You might also check the MorningStar TS MPPT controller series and the Midnite solar Classic charge controllers too... They may support 36 VDC battery banks (MorningStar probably needs an optional computer interface/converter).

    -Bill

    Nope, all TriStar Mppt has builtin RS232 connector and on the 60 amp unit you can use the ethernet or rs232. The TriStarMppt can be programed for custom voltages, like 36V

    The SunsaverMppt is the one that needs the converter
  • GaryGary
    GaryGary Registered Users Posts: 9
    Re: Powering my house from my mower
    BB. wrote: »
    Yes, you are correct... 36 VDC is virtually non-existent with standard solar PV systems, trucks, or other vehicles. You might find some 36 VDC UPS systems (Tripplite, etc.). And Outback has a 32 VDC inverter (perhaps you can configure for 36 without too much trouble).

    About the only common 36 vdc system seem to be (older?) boats... So, you may end up having to buy expensive hardware (charge controllers, inverters, etc.) to use your batteries for "free" backup.

    You might also check the MorningStar TS MPPT controller series and the Midnite solar Classic charge controllers too... They may support 36 VDC battery banks (MorningStar probably needs an optional computer interface/converter).

    -Bill

    Thanks Bill,

    I did look into the MorningStar MPPT, and it does support 36 volt battery packs -- its not in the basic specs, but they have a web page on how to do it.

    The thing that I'm not so thrilled about is that you have to use the PC software to do the 36 VDC setup, and I'm not sure I want to have to go through that in a emergency situation with the power out and the wind blowing ...
    I guess if it retained the settings even when its disconnected from both the PV array and the battery pack, that would be OK.

    Gary
  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: Powering my house from my mower

    You only program the MorningStar products once, all settings are stored in NVram
  • GaryGary
    GaryGary Registered Users Posts: 9
    Re: Powering my house from my mower

    Hi,
    Just wanted to thank everyone for the inputs -- very helpful.

    I've about 99% decided to buy the Xantrex 150 MPPT unit on Monday. Its more than what I need, but more flexible to meet future needs, and not a whole lot of other choices anyway.
    Soldering new battery cables today :)

    Gary
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Powering my house from my mower

    Instead of soldering the cables, can you find a local battery distributor that can crimp up a set for you? Or, you can use a hammer crimper. They are not too expensive (~$30):

    wind-sun_2173_5106713
    This simple, inexpensive crimping tool can be used to crimp connectors on #8 through #4/0 AWG wire. Spring loaded pin locks in ... the pin holds the connector securely during crimping. Use with a hammer or vice. Though not quite as easy as the professional production ...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset