Amateur questions - how to reduce DC amps ? Auto shut off?
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Posted by buddy on July 19, 2008, 11:16 pm
Please log in for more thread options more than the names of various components) how to reduce DC amps? I want to heat a container of water in an automotive use. I have one of those cheap "heating coils" that you plug into the cigarette lighter outlet, and drop the coil into a mug of water to make instant coffee or tea. But two problems: - I powered it from a battery charger and it drew 10 amps, way to much - after only a few seconds, it gets way to hot to touch. I don't want it hotter than, say, 100-120 F. I think these two goals are compatible, but I don't know how to reduce the amps. 2. I want the above to shut off automatically, both when power is removed (i.e. car turned off) and after some amount of time, say 10 minutes - just like the rear window defroster. How to do this? Thanks in advance for any ideas, buddy | ||||||||||||||||
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Posted by RFI-EMI-GUY on July 19, 2008, 11:34 pm
Please log in for more thread options A simple way: http://europe.hbc.honeywell.com/products/pdf/en0r8445uk07r0402.pdf It won't reduce the "amps" but you can set to shut off when the water reached the desired temperature. It will of course come back on if the water cools off. Also, you have to keep water in contact with the heating element and the thermostat bulb or the element will continue to heat up. Since you don't explain what your end goal is, I can't advise you on the safety of what you are doing. I would suggest that given the possibility to over heat if the water runs out, you should have a float switch to prevent the element from coming on without any water in the container. -- Joe Leikhim K4SAT "The RFI-EMI-GUY"© "Treason doth never prosper: what's the reason? For if it prosper, none dare call it treason." "Follow The Money" ;-P | ||||||||||||||||
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Posted by MooseFET on July 19, 2008, 11:59 pm
Please log in for more thread options > 1. =A0Can someone explain, (in simple language, I basically know little
> more than the names of various components) how to reduce DC amps? This is really more of a "basics" question than a "design" question. You also have a "design" question later. First make sure you are reading this with the right font. The "*"s should line up in the lines below. *MMM*MMM*MMM* *III*III*III* *---*---*---* Change the font until they do. The term series means like this: Wire More wire 3rd wire ------[Item1]------------[Item2]------ If you connect two identical resistive heater in series, the total power and the current will be reduced in half. Each heater will end up with 1/4th the power going to it. I =3D V / R I is current V is voltage R is resistance Hooking stuff in series makes the resistances add. P =3D I^2 * R P is power >
> I want to heat a container of water in an automotive use. =A0I have one > of those cheap "heating coils" that you plug into the cigarette > lighter outlet, and drop the coil into a mug of water to make instant > coffee or tea. =A0But two problems: > > - I powered it from a battery charger and it drew 10 amps, way to much > - after only a few seconds, it gets way to hot to touch. =A0I don't want > it hotter than, say, 100-120 F. You can buy a thermostat that kicks off at 100F. If you wire this in series with the heater (and it can take the current), you will have something that turns on until the water heats above 100F and then off until it cools below 100F. It will cycle on and off holding the temperature in a narrow range. If your thermostat can't take the current: http://dkc1.digikey.com/US/EN/PDF/T082/Section.html look around page 2063 Digikey may also have the thermostat you need. >
> I think these two goals are compatible, but I don't know how to reduce > the amps. > > 2. =A0I want the above to shut off automatically, both when power is > removed (i.e. car turned off) and after some amount of time, say 10 > minutes - just like the rear window defroster. =A0How to do this? If you can live with very inaccurate timing, you can use a second small heater and a second thermostat and a relay. A push button will start the timing. Hefty push button ! ----- ---O O------- ! ! ! ! ! Contacts ! ! 0f relay ! ! / ! +12V -+---/ O--------+---+-------- -------------> To heater
!
[Therm] [ostat] ! +------------ ! ! ) [Small ] Coil of ) [heater] relay ) ! ! GND GND When the button is pressed, the relay contacts close because its coil gets power. As long as the coil continues to get power, the contacts will remain closed and the heater will remain on. If the +12V input goes away, the relay is de-energized. If the small heater heats the thermostat hot enough, the coil gets de-energized. The thermostat and small heater should be inside an insulated housing. Screwing them both down onto a block of aluminum would be how I would hold them in place. The more aluminum in the block, the longer the delay. This is extremely crude but these sorts of things are hard to break. >
> Thanks in advance for any ideas, > buddy | ||||||||||||||||
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Posted by buddy on July 20, 2008, 2:31 am
Please log in for more thread options Thanks for all the replies. You're right, it might help if I explain
what I'm doing. I am going to make and experiment with an HHO electrolyzer for my car. I'm thinking ahead to winter time. I do not want to adapt the heating coil I used as an example; I want to have a stainless steel 1/4" threaded rod as a heating element, about 1 foot long running through the tank. I don't want the rod/heating element to get more than about 120F because it will go through, with sealant, the acrylic case. I found this circuit which is supposed to turn on a heating element (he uses a metal plate under his electrolyzer "jars") until the temp reaches 72 , then turns off (he also incorporates turning on a fan at 115 but I am not doing that). http://flapdoodledinghy.com/HHO_control.html I don't understand how it is "set" to turn off at 72. (well I don't really understand the schematic itself.) I want to have a small in-car control unit which displays the temperature of the electrolyte with LCD or LED readout. I found this link http://gaugeplans.com/ It says it can be fitted with an external probe. He will email a schematic if I email asking, but the picture looks like it requires a much bigger board than the readout itself. I want to keep the control unit as small as possible. I also found this: http://www.fishersci.com/wps/portal/!ut/p/_s.7_0_A/7_0_K9/.cmd/ad/.ar/sa.PortletNAVAction/.c/6_0_AJ/.ce/7_0_BEG/.p/5_0_33V/.d/2?LBCID=82975277&LBCID=82975277&ru=http%3A%2F%2Fprodwcsserver%2Fwebapp%2Fwcs%2Fstores%2Fservlet%2FFisherItemDisplay&catalogId=29104&productId=2851412&parentProductId=3789599&langId=-1&parent_category_rn=&distype=0&accessories=false&fromCat=yes&catCode=RE_SC&fromSearch=Y It has a 10 foot probe wire which is long enough to reach into the cabin, and the probe is stainless steel, also a requirement. But the LCD is not lighted so it's hard to see (for that reason, I'd rather have an LED display), it is battery powered but I want to use vehicle power, and no "output" to use to set on/off for a heating element. The way I want this to work in wintertime - or maybe I'm dreaming to think I can do this - is like this: Car off: 1. I know I'm going somewhere in about 20 minutes, so I go out and push a momentary button to turn on the heating element. It heats (LED shows it is on) until the electrolyte temp is about 70, or about 10 minutes auto-off (like the rear defroster), in case I change my mind about going somewhere 2. I go out to the cold car in wintertime and drive away, the electrolyzer power switch is on - it's always left in on position - but it still doesn't go on until the temp reaches 60, then its LED shows me it went on. The heating element goes on, an LED shows me its on, it stays on until electrolyzer reaches about 70. 3. As noted, heating element must not get hotter than 100-120. Is this doable? Thanks, Buddy | ||||||||||||||||
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Posted by Phil Allison on July 20, 2008, 3:13 am
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"buddy " = TROLL > Thanks for all the replies. You're right, it might help if I explain
> what I'm doing. > > I am going to make and experiment with an HHO electrolyzer for my > car. ** Say no more. This absolute, know nothing loon thinks perpetual motion is a reality. Probably talks to space aliens and practices Scientology as well. Ignore this ridiculous TROLL ..... Phil | ||||||||||||||||
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> more than the names of various components) how to reduce DC amps?
>
> I want to heat a container of water in an automotive use. I have one
> of those cheap "heating coils" that you plug into the cigarette
> lighter outlet, and drop the coil into a mug of water to make instant
> coffee or tea. But two problems:
>
> - I powered it from a battery charger and it drew 10 amps, way to much
> - after only a few seconds, it gets way to hot to touch. I don't want
> it hotter than, say, 100-120 F.
>
> I think these two goals are compatible, but I don't know how to reduce
> the amps.
>
> 2. I want the above to shut off automatically, both when power is
> removed (i.e. car turned off) and after some amount of time, say 10
> minutes - just like the rear window defroster. How to do this?
>
> Thanks in advance for any ideas,
> buddy