12 Volt Inverter Meets 36 Volt Golf Car

[LowGear]

I bought this 12 volt inverter to put on my truck but dreams often aren't well thought out.  So here I am with a 12 volt 1500 watt inverter and a 36 volt golf car sporting three 12 volt batteries.  Do I put it across battery number one, two or three?  The charger is 36 volt.

Casey

[BruceM]

Just discussed in this section, previous topic.
http://www.microcogen.info/index.php?topic=735.0

[mike90045]

That will be tough to do, its bad on the batteries and unbalances the string, and ruins the "tapped" battery.  If you were careful, and changed to a different battery 3x a day to spread the load evenly, it might work, but a PITA.

[BruceM]

There's no way to manually "match" discharge on each battery, and then get them "even" again via charging at 36V in series that isn't going to ruin the batteries with regular use.  The batteries would have to be individually charged to full via 12V charger. 

Possible solutions:
1. Get a 36V inverter.
2.Make a battery series/parallel switching system so that when your golf cart is being used as your remote AC power source, the power to the golf cart is disconnected, and the batteries are reconnected to the inverter as 3- 12V batteries in parallel. 
3. Get a 36V to 12V buck converter with enough ampacity at 12V to run your inverter.

Using the golf cart as a roving power source would be very handy, it's a pity 36V inverters are less common and are priced accordingly. 

[mobile_bob]

probably better off just buying another deep cycle 12volt battery, tote it around on the cart with the inverter
and recharge it with a separate charger back where you park it while charging the 36volt battery with its separate charger.

usually for remote power use, the need is fairly short lived, so in all likelihood a single 12volt would probably suffice

bob g

[BruceM]

I just spent some time looking at the 36V options- it doesn't look good.  DC-DC inverters aren't commonly in high enough amps for a even a 1000watt inverter.  Triplite makes an inverter for 36V but it's $900 and a bulky inverter/charger unit. 

The battery interconnect switching from 36V series to 12V is a bit of a bitch because of the relatively high currents involved.  It's not common enough for there to be commercial products- so you'd have to make up something via the monster Anderson connectors- and plugging/unplugging those monsters isn't a great solution.

I suspect Bob's suggestion is the easiest and most practical solution. 

I did see references to 32V marine inverters that can be operated on 36V but didn't follow up.  My experience is that most things "marine" are specially priced.  Still, there is a beauty to not having a separate battery and charger, and that might make the Triplite 36V inverter/charger or some marine inverter worthwhile for you.  Depends on how long you will need the mobile power capability.   

[rcavictim]

Casey,

You may be all set if you can find a computer UPS that has been discarded only because the batteries have gone bad.  Three 12 volt battery, 36 volt units are fairly common in the 1500-3000 VA models.  Look for APC units on ebay.  Youur bonus will be a pure sine wave inverter.

One caution.  Some UPS's cannot be started from a stand alone condition, they need to have been seeing mains power first.  Some start fine completely islanded.  I don't know how to predict this so best to check with the seller before you hand over your money.

[BruceM]

Great tip, RCAvictim!

[LowGear]

Thanks for all the good advice. 

I did go back and read Bob G's thread.  A little over my head but the plan to put the inverter on the center battery is over.  At $200 a piece I would have been real bummed by a dead Trojan.  Yes, there worse case scenarios for a dead Trojan but at 66 those rushes are pretty much over.

I had kind of mused the double load switch that Bruce M suggested - Really.  ("Oh, I thought of that" is one of my buttons!)  Finding a 6 pole really heavy duty switch slowed me right down.  I guess I could use six double throw knife switches but that's too much out of Fibber McGee's closet.

The new dream was to not spend very much money to use a pretty neat piece of equipment that's just lying around the garage.

Now that dead battery UPS idea.  Wow!  I wonder where to shop for one of these?  Ebay and the County electronics recycling shop?  But I'd still have the inverter out at the garage.  If you see one of these UPSes that wouldn't require a trailer please let me know.

OK!  I did not tell the whole truth.  I'm putting the batteries, motor and electrics (no electronics in this 40 year old car) into a gutted Polaris ATV. 

Casey

[Jedon]

OK!  I did not tell the whole truth.  I'm putting the batteries, motor and electrics (no electronics in this 40 year old car) into a gutted Polaris ATV. 

I have a dream of converting my Recreatives Max 2 6x6 to electric/hydraulic.

[LowGear]

Hi Jedon,

The manufactures are actually coming out with their own designs.  I'm sure they'll be great but the Polaris is close to $10,000.  Nice stuff costs more.

I've actually got my rig gutted.  I'm doing the battery plate drawings for the steel shop that has a computer controlled flat bed plasma cutter.  They only charge twice as much to let you watch.  I did fire up the recipricating saw to get the tranny out.  The photo shows you what brought this guy down.  Get out there and turn a wrench today.


HEY!

Last night's twilight dreams were of three double pole - double throw switches.  120 volts at 2000 watts peak is almost 17 amps.  12 volts at 2000 watts is about 167 amps.  Either my math is down to public school standards or that's a lot of current.  I wonder where I'd find a switch that can handle that kind of current?

Casey

[cognos]

So - what causes a failure like that one? It looks like freezing. But - in Hawaii? What happened - park it in a giant freezer with a tranny full of water?

[BruceM]

Harbor Freight and others carry a single pole battery disconnect switch that can handle 200 amps.  If you put two in middle of your series string to open each 12V battery set, then you could lead out all three 12V batteries to the giant size (175 amp) Anderson Power Pole connectors.  Then you'd have to plug in your 12V in parallel cable (3 double Andersons connected to your 12V inverter). If you ever forget to open the switches, though, it could explode and kill you.  Better put a big fuse in each 12V lead out to prevent that. 

If you were daring, you could make up the parallel 12V connectors with the smaller Anderson power pole connectors, as each pair would be carrying less than 60 amps.  Electric RC airplane guys abuse the hell out of the power pole connectors and they seem to hold up OK.  Finding some fine stranded #4 wire might be tricky.

[rl71459]

Ive seen that type of failure before.... When  the chain derails and wads up between the case and
the sprocket! OUCH! When I was a teen I was a wrench @ a motorcycle shop. Seen it multiple times
usually on dirt bikes.

Sometimes you can pick up one of those bikes real cheap.

Rob

[LowGear]

Rob has it right.  We used to called it stacking the chain.  A real shame as the rest of the unit is in nice shape.

Call me old fashioned but if it ain't fool proof then I ain't going there.  I'm neither infallible nor immortal any more.  Like the saying goes "Never trust anyone under 30"!

I think three double pole – double throw switches just might do it unless someone can come up with some sort of six pole duplex switch.

Casey