74 volt dc converters

I get a call every month or so from an engineer who wants to run 12 volt equipment in a 74 volt locomotive. We have finally decided to develop a DC/DC converter for this purpose.

But then I realize that I don't know much about the 74 volts DC. Does anyone know what the voltage range is?

Or where it comes from? How many cells are in the battery?

Also how do you connect to the 74 VDC in the locomotive?

Best regards
wiz

Locomotive systems run at 64 VDC. The 74Volts is there when the engine is running jst like on a car where the 12 volt battery is actually being charged a little higher, around 15 or 16 volts. Enough on that though.
Most of our battery systems consist of two 32 volt batteries connected in series and most of our starters are 32volts also connected in series except for a few locomotives acquired through mergers which have two 64 volt starters hooked in parallel.
As far as running things in the cab. Most of our cabs have what looks like a standard 110 volt outlet in them for running test equpment or whatever. There is 64 volts dc at these outlets and we have plugged regular 110 volt computer power slupplies into them for running laptops with no problems although I would not say that this would work on every one and I would be a little afraid to try it on one of my own computers for fear of burning something up.

Thanks, this is very helpful.

I expect that some computer power supplies would work at
74 volts DC, though since they are usually designed for
90 to 280 volts AC, they will be somewhat out of their
voltage regulation range, and the
extra input current needed at the lower voltage woud cause
them to get hotter than normal.

If I get some free time in the lab I'll check to see what
our laptop adapters do.

The 74V system on most locomotives generally ranges from about 65-75VDC with the engine running but is very "dirty" power with regards to spikes and frequency variances. I often run a tremendous amount of equipment onboard locomotives for testing and if you are designing something to run say a 12V coffee pot, once you figure out the load of the accessory then use ohms law and put the correct value resistor in the circuit. If you are trying to run something delicate like a laptop, there are companies out there that manufacture 74VDC to 74VDC filters, 74VDC to 110VAC, and 74VDC to 5,12,15VDC power supplies and inverters. They are not cheap.

Most locomotives built since 1980 or so have a 5,12, and 15V DC power supply on board inside the electrical locker but they NORMALLY will not stand up to much more than 1 amp of additional draw and it really sucks when you tie into it and turn on your accessory and kill the whole locomotive or consist and puts the train in emergency.

Also, never try to tie in the the AC system used for the accessory or excitation system (i.e. aux gen, exciter, etc) on units as in some places you can get pretty measure close to 110VAC but the frequency will go from anywhere from 40 to 200Hz and fry any "off the shelf" item made to run on household power.

Most EMD and GE locomotives have a 74VDC plug that will accept a normal household appliance plug somewhere inside the cab.

To give you some idea, filtered 110VAC inverter that can run reliabily off the 74VDC circuit is well over $1000 if you want to run something like a computer or TV off of. TecTronics of Canada is one source. You can find cheaper ones but they will not last or will burn up whatever you are trying to operate due to allowing spikes to pass through. IN short, for cheap 12V appliances, do the math and put a resistor. For expensive stuff, spend the money for a good quality 74 to 110 inverter.

Good luck!

Thanks, Jesse for the further help. We are redesigning one of our DC/DC converters so that we can supply filtered, reliable 12 (or 13.8) VDC with an input of 65-75 VDC. This should be reliable and inexpensive (less than $150) if we do our design right However, if this is going to be useful in locomotives we need all the advice we can get, since we don't have a train we can do tests with

Last thing, try contacting a nearby short line railroad as most of the time, these guys are more than willing to help you for minimal expense. Go to a search engine and find the web site for the American Short Line and Regional Railroad Association. It will pull up every short line railroad in the US and give you a link to that roads web site and contacts if they have one. If no web site, it will give you an address and phone number. Good luck!

Hi
It depends on how much current you will need. anything bbelow 1 amp is fairly east but if you need several amps there are other parts that can be used with out having ot use switching powersupply methods.
Give me an Idea or what current you are wanting and I may be able to make a good and simple circuit for you to use.
you might also try looking up circuits on the internet for goodones too
Andrew Martin
TWVRPS

We are a small power supply design/development company and have
several products that are close to this already. The new issues
are that anything over 60 volts is considered a shock hazard
and we have to design around that.

Then there are the issues of noise, spikes, and ease of use.

Best regards
wiz

Be aware that in a locomotive, both the positive and negative sides of the circuits have to be isolated from ground. Depending on the source of power you use, a 12 volt device with a chassis ground may contribute to ground relay problems in the locomotive if it is attached by metal to the structure of the locomotive. Years ago I saw a switcher at a foundry that had a radio powered from a dropping resistor, and combined with other grounds present, the radio was able to kick the ground relay and prevent the locomotive from loading.

cb&q bob wrote:...Most of our battery systems consist of two 32 volt batteries connected in series and most of our starters are 32volts also connected in series except for a few locomotives acquired through mergers which have two 64 volt starters hooked in parallel...

on all of the units i work on, we have 8x 8v batteries all in series, and all our starters are 32v in series...


edit...

i just got to thinking at work today what the fridges on our units run on, and they run on 120vac... there is an inverter to go from 74vdc to 120vac.. it is a smallish box and transformer... stick some alligator clips on the leads for it [and feed the 74vdc through a bridge rectifier for idoit proofing] and you could have your self a small box 10"x10"x4" that could have a couple of outlets on it and just clip it straight to the knife switch

Was a unit the night, pulled into the siding, we sat for about 2 hours, and as I was staring at the ceiling, I notice a sticker for a website :

http://www.locoverter.com/

Interesting. I have seen fellow conductors and hoggers who have tied into the knife switch in the circuit breaker panel as well as the outlet (if equiped on a unit) and power thier cell phones and laptops.

Folks, we have done all the research for you. At locoverter.com, we have DC to DC converters that will work anywhere between 75 and 36 volts DC, regardless of voltage spikes or frequency swings. They convert the locomotive DC voltage to 12 volts DC and allow you to power any of your 12 volt DC equipment. We also sell inverters that change the voltage to 110v AC. You can safely power any of your equipment with our products. Locoverter products were designed by railroaders for railroaders. Please visit our website for more information. www.locoverter.com

doowoppie2000 wrote:Hi
It depends on how much current you will need. anything bbelow 1 amp is fairly east but if you need several amps there are other parts that can be used with out having ot use switching powersupply methods.
Give me an Idea or what current you are wanting and I may be able to make a good and simple circuit for you to use.
you might also try looking up circuits on the internet for goodones too
Andrew Martin
TWVRPS

Hello: Is it possible for you to send me the circuit you mention.

http://www.powerstream.com/dc-72.htm $131.60 including cord and cigarette lighter socket.

Big enough to run a 9 amp 12 volt coffee maker.