Heating Element Control

[Bustard]

Good Afternoon,

I am looking for some help as i am electrically challenged

My setup has a 4500W element and a 2000W element. the 2000W element is switched on for heating up only and the 4500W used during distillation. The element is made up of 3 x 1500W elements and to date used on 220V using a pot variable ssr as described by Cranky.The three elements are bridged and connected to L and N

I am moving to a 380V 3 phase power supply and would like to know if i can split the phases and add another two ssr (one ssr for each element) and control all three of them with one pot. The ssr is 40A units and each controlled by 500 ohm variable resistor. I have spare ssr and cost prohibits me from buying a 3 pole 380 volt ssr.

Not sure if the question is clear

Thanks in advance

B

[sw_reijnders]

okay,

be careful
each element shoud have a resistance of
1500w/220v=6.81A
220v/6.81A=32.3Ohm

now if you put this on 380v your current will be
380v/32.3Ohm= 11.8A
380v x 11.8A x 3 elements = 13.400 watts
But as you connect this in a 380v configuration you have to multiply the current with √3
so your current will be 11.8A x √3 = 20.4 Amps on each phase.

all calculated with Ohm's law
P=UxI
U=IxR

[rad14701]

okay,

be careful
each element shoud have a resistance of
1500w/220v=6.81A
220v/6.81A=32.3Ohm

Here in the US the voltages are 120V and 240V, not 220V... Not a huge difference for calculations but you might as well get used to quoting it accurately... My 240V line voltage measures 238V, as do most other 240V circuits I've tested...

[Bustard]

Thank you for the replies,

To clarify our supply on three phase have three hot wires, a neutral and an earth wire.
The voltage measured between hot wires is 380 volt and measured between any hot wire and neutral will measure between 220 and 238 volt depending on area.

By splitting the phases I will have a ssr on each hot wire - and in turn feeding an element.

My question still is can I control all three ssr with one pot of 500 ohm or should it be a different value. If so do I wire the pot and ssr in parallel?

Thanks
B

[skow69]

Hey reijnders,

I'm not reaolly a triple phase guy, but I think there is a problem with your calcs.

If you really had 20.4 amps on each phase, then total power would be 380v * 20.4a = 7752 watts per phase X 3 phases = 23,256 watts total. That would mean that your 4500 w element had become a 23 kw element.

Bustard,

No you can't run three ssrs on a single potentiometer. You need a 3 gang pot. That's 3 identical pots in a stack with a single shaft that turns all three wipers in unison. Then run each ssr through its own "gang."

Good luck.

[Kegg_jam]

Three phase Y connected transformer correct?

[skow69]

You sure it's not delta. My recollection is phase to ground is 240 VAC, phase to phase was 208 VAC. But it's been awhile.

[sw_reijnders]

Hey reijnders,

I'm not reaolly a triple phase guy, but I think there is a problem with your calcs.

If you really had 20.4 amps on each phase, then total power would be 380v * 20.4a = 7752 watts per phase X 3 phases = 23,256 watts total. That would mean that your 4500 w element had become a 23 kw element.

no it is correct.
it took me a while to accept it, but I still don't understand it
I have a 9000 watt element myself.
3 elements of 3000 watt on 400 volts 3-phase in the Netherlands.
it should be 3000w/400v = 7,5A
but if I look at the ammeter it shows 13A
The element will give 9000 watts of heat, but it pulls 13A on each phase. Which is exactly the √3 (1.73) factor.

Bustard,

No you can't run three ssrs on a single potentiometer. You need a 3 gang pot. That's 3 identical pots in a stack with a single shaft that turns all three wipers in unison. Then run each ssr through its own "gang."

Good luck.

actually I think he can, but he needs a different SSR's

if you look at these SSR's, they are controlled by 4-20mA signal.
So if you have a 24 volt powersupply, a Potentiometer of 1200-6000 Ohm and 3 SSR's in series circuit.
MilliAmps are measured in series and I think you can see these 3 SSR's as 3 mA-meters.
It Could work in theorie.

I have 3 of these SSR's and this is something I still have to test.
http://www.ebay.com/itm/1pc-KYOTTO-Curr ... XQlrxRaDoH" onclick="window.open(this.href);return false;" rel="nofollow