A realistic approach is probably a supply that would handle the POWER level required paralleled with a car battery to provide short current peaks. A microwave oven transformer with the secondary removed and a new one wound MAY be about right for the level of power desired. These have something special done to the magnetic path - to make them droop under high load AFAIK, so they may not suit. These operate at around 1 KVA but not for long periods. Enthusiastic fan cooling may help although use of more than one transformer may be advised. New transformers of 1 KVA rating (80A at 12v or 40A at 24v) sell here for about $NZ 250 = about $US125 = $A200 so presumably they are similar there as copper and steel is pretty universal technology. The battery would not need to be deep cycle - rather something intended for float use. Power Schottky diodes are going to save some heat at these current levels (and add some dollars). Use of triacs in a synchronous rectifier may be a cheap solution and simultaneously allow a dgree of voltage control under the immense load variations. . Russell McMahon _____________________________ - www.easttimor.com Updated regularly: 100,000 refugees STILL in West Timor face starvation! - www.sudan.com And you think Kosovo and Chechnya are bad! What can one man* do? Help the hungry at no cost to yourself! at http://www.thehungersite.com/ (* - or woman, child or internet enabled intelligent entity :-)) -----Original Message----- From: Gennette Bruce To: PICLIST@MITVMA.MIT.EDU Date: Monday, 27 March 2000 18:25 Subject: Re: [OT] PSU for slotcars >At last ! An answer from someone who has a slot car power system. > >Seriously though, this has always been the traditional answer - use some car >batteries to run the slot cars, one (or more) per slot car. The better >systems would use continuous, monitoring chargers for each battery. > >So what would you need for 8 tracks . . . >8 deep cycle batteries >8 isolating diodes >8 battery charger circuits set to 14.5V (13.8 + diode drop of 0.7V) @ 1.2A >2 rectifiers >2 transformers (18V @ 6A) > >Except for the batteries I would estimate that this could be built for about >AU$300 (US$200). Then there are the batteries. Car batteries are >unsuitable - they are designed to give a big push for a short time and be >recharged *IMMEDIATELY*. Deep cycle batteries are designed to provide >moderate output for long periods, but must not be discharged too deeply, >(discharged to only about 5% below max is recommended for maximum life). > >6 hours continuous flat-out running of a slot car drawing an average 4A (3.2 >from battery & 1.2 from charger) uses 19.2AHr, and can be replaced over 18 >hours at 1.2A from the charger (21.6Ahr). This would drain the battery by >around 3.2A x 6Hr = 19.2Ahr. Of course actual usage would normally be less >than an average of 4A so the power usage time would be spread over a longer >track usage time, probably around 9 or 10 hours per 24. > >So you need to buy batteries with at least 400Ahr capacity to keep the >discharge per cycle drop below 5%. (Each extra 5% discharge per cycle >halves battery life - that is a battery regularly discharged to 10% below >max will only last half as long as one regularly discharged to 5% below max. >If discharged to 15% below max per cycle it will only last a quarter as long >as a 5% discharged per cycle). > >400Ahr deep cycle batteries are about AU$150 each (US$100). And you need 8 >of them. That makes a total of AU$1500 (US$1000) for 8 tracks *AND* you are >up for another AU$1200 (US$800) every 4 or so years. > >No wonder your friend wants an electronic solution. So can anyone suggest a >proper solution. What we need is a 14.5V @ 80A (1200VA) low droop power >supply with 8 isolating diodes and 8 capacitor tanks. > >Don't be afraid to suggest expensive solutions (see cost of alternative, >above). > >Bye. > > -----Original Message----- > From: John De Villiers [SMTP:bbj@PLZ.CO.ZA] > Sent: Monday, 27 March 2000 0:10 > To: PICLIST@MITVMA.MIT.EDU > Subject: Re: [OT] PSU for slotcars > > 1 AMP doesnt even turn my car's motor. > > These little things do a 35 meter figure 8 track in under 4 seconds > > Also, you Brake by shorting its power leads. A PSU for these will >have to > have some serious overload protection built-in > > We use several heavyduty 12V batteries wired in parrallel ( for >those enduro > envents ). > > > Quentin wrote: > > > > > A friend of mine asked me about making a PSU for the slotcar >track for > > > his club. Seems like these things needs lotsa power. After he >gave me > > > the specs I went UHHMMM...... > > >