12 Volt Inverter Meets 36 Volt Golf Car

[mobile_bob]

here is another possibility that might work, the operative word here is "might"

you have 36volts, and there are lots of 48volt dc inverters, and ups systems that use that dc front end voltage
so...

add a 4th battery to the string, so you have 48volts to run the inverter, and 36 to motivate
when you come back to dock for charging, connect the 36 vdc charger as normal, and another smaller 12volt charger
to the extra battery.

that way you don't need a bunch of high power contactors, relays or switches, the money saved will buy the extra battery
leaving you to find a ups system with a 48volt bus or a 48volt inverter.

an apc 2200xl will put out 1600watts and is 48volts front end, they are fairly common in the surplus market with dead batteries.
also an apc 3000xl that is rack mounted 2U size is good for ~2700watts and are also fairly common
both put out very nice sine wave which may or may not be important to you.

this method would provide for the power you need without tipping over the balance of the 36volt bank.

bob g

[M61hops]

What about adding another 12V battery to the vehicle drive system and using a 48V inverter to make AC as well as drive the vehicle?  I doubt the extra voltage would hurt the drive system and it would add motive power.  I guess you would have to find a 48V charger, I don't know how common they are but you could sell the 12V inverter and the 36V charger then put that cash towards the project.  My $.02 and worth almost that much?                        Leland

[BruceM]

I also noted in searching for 36V inverters that some golf carts are being converted to 48V.  

There is an issue with AC relays or switches being used for DC.  If you  switch  when current being drawn, the ARC WILL NOT SELF QUENCH as in AC use.  Instead, you will have melting and smoke.  So unless the switch/relay is rated for your intended DC voltage and current, you will have to ONLY SWITCH WITH ZERO CURRENT.  Again, this is a serious safety issue- a moments mistake could cause a melt down and fire.

In working with 120VDC for lighting I became very aware of this- even 30A heavy duty industrial AC switches will arc and smoke on the very first "off", with just 250 watts of load. (About 2A at 126V).  Cooper once made a switch that was rated for 150VDC, 4A, but it was discontinued 2 years ago.  I had to scramble to find the last of that production.   I  have few double pole switches (also no longer in production) that just happened to work for DC.  In one morning, I fried over $150 worth of industrial switches, of different brands and models, trying to find an alternative switch!

[LowGear]

Time and thinking march on.

I've done a drawing of what could be done with three double knife switches like were used close to a century ago and would be simple, cheap but not "Neat".  And if I got the sequence wrong it would result in smoke and no mirrors.  I would like to know a couple of things:

• Does the drawing bring to mind any simple, cheap and neat solutions?
• What would the nomenclature for this switch or relay be?

Casey

[mike90045]

6PDT
(break before make)
But that switch (or relay) needs to carry your full DC power (100A)
You might be able to get a series of "contactors" to switch the high amp path.

[rcavictim]

I also noted in searching for 36V inverters that some golf carts are being converted to 48V.  

There is an issue with AC relays or switches being used for DC.  If you  switch  when current being drawn, the ARC WILL NOT SELF QUENCH as in AC use.  Instead, you will have melting and smoke.  So unless the switch/relay is rated for your intended DC voltage and current, you will have to ONLY SWITCH WITH ZERO CURRENT.  Again, this is a serious safety issue- a moments mistake could cause a melt down and fire.

In working with 120VDC for lighting I became very aware of this- even 30A heavy duty industrial AC switches will arc and smoke on the very first "off", with just 250 watts of load. (About 2A at 126V).  Cooper once made a switch that was rated for 150VDC, 4A, but it was discontinued 2 years ago.  I had to scramble to find the last of that production.   I  have few double pole switches (also no longer in production) that just happened to work for DC.  In one morning, I fried over $150 worth of industrial switches, of different brands and models, trying to find an alternative switch!

Bruce,

May I suggest the solution to your problem will be in the use of a DC rated circuit breaker instead of a wall switch.

http://www.solarseller.com/dc_circuit_breakers__dc_circuit_breaker_ul_listed_to_125_volts_dc.htm

[LowGear]

Hmmmmm,

I seem to be missing something here.  These switches / relay will need to be like a three way switch in the wall not just an off - on switch, more like either - or.

The good news is that I would be the only person authorized to "throw" this switch.  After all, I am the Supreme Commander of Camp Aloha.  I can't see the time that I would throw the switch while riding the machine.  Those double pole knife switches are looking more real all the time. 

I wonder what the current draw is on this 36 volt DC golf car motor is?

Casey

[LowGear]

So would this then be a three pole, single throw, six gange switch / relay?

Casey

[Lloyd]

It would be a Kraus-Naimer Rotory switch, dc rated...but never switch under load, or break before make switch.

http://www.krausnaimer.com/0/prod.htm

Lloyd

[LowGear]

Hi Lloyd,

Now them is some switches.  The monitor got kinda jittery and started smelling just like a federal printing press - over worked.

I couldn't find a place to inquire about the cost of their really really nice looking switches.  Would you direct me to a vendor?

Casey

[Lloyd]

Casey,

they are sold by just about every marine store that sells marine electrics...online and at bricks and mortar.

just use the configerator, to build the switch, it will generate a part number and use that to order your switch.

lloyd

[LowGear]

Hi Lloyd and Others,

I couldn't figure out that switch builder program so I inquired at a couple of their retailers.

I'm thinking those "Marine" switches are going to be on the other side of priceie.  How about this switch on Ebay:

http://cgi.ebay.com/Generac-Load-Manager-Generator-Switch-/140403369262?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item20b0b1652e

Casey

[Lloyd]

Casey...

I don't think it will carry the dc volt/amps you need. AC rated is the problem...the contacts just burn up when subjected to the arcing of dc current...that's why dc switching has silver alloy contacts.

A lower voltages, mean higher currents and more hotter arcing, at switch time, also they can't carry the heat of the high current after switching...Ive seen many an improper ac device used in dc circuits that just melt or burn up...and cause fires..not to mention short circuit and fried electrical devises.

lloyd

[mike90045]

Even if you don't switch while amps are flowing, you need to have contacts that can carry your motor's running amps.  That will be tough.

Or 6 of the marine battery 1-2 switches would work.

[veggie]

Hmmmmm!
Sounds like it might be cheaper (and much simpler) to just buy a separate 12 vdc deep cycle battery for $170 ?

veggie