Immersion heater

robertj

Active member
Joined
13 May 2007
Messages
7,313
Visit site
Does anyone know if a good supplier of immersion heaters?
I’m specifically looking to fit a 900w one to my calorifier soon.
It has to be a lower rating as I intend on using it with a Honda generator eu10i which is rated at 900w constant.
 

Bilgediver

Well-known member
Joined
6 Jun 2001
Messages
8,220
Location
Scotland
Visit site
Check the spec of the Honda Generator as it is not unusual for manufacturers to quote power ratings at a power factor of 1 . Your power factor could be as low as around 0.75. so would be overloaded. Might need a more powerful generator.
 

robertj

Active member
Joined
13 May 2007
Messages
7,313
Visit site
Check the spec of the Honda Generator as it is not unusual for manufacturers to quote power ratings at a power factor of 1 . Your power factor could be as low as around 0.75. so would be overloaded. Might need a more powerful generator.

1000w max
900w continuous
 

Alan S

Well-known member
Joined
5 Jun 2016
Messages
632
Visit site
Immersion heater is a resistive load. Does that not mean the power factor will be 1?
I think I would still allow a little margin as I think manufacturer's claims are often optimistic.
 

superheat6k

Well-known member
Joined
10 Jan 2012
Messages
6,785
Location
South Coast
Visit site
Immersion heater is a resistive load. Does that not mean the power factor will be 1?
I think I would still allow a little margin as I think manufacturer's claims are often optimistic.
Not quite, because the alternator is still an inductor, so the overall circuit has some inductance hence the power factor will not be unity even with a purely resistive external load. Not a very efficient way to heat water, and I would suggest a max of 750w on a 900w max output genny is more prudent.
 

captainboo

Active member
Joined
11 Dec 2008
Messages
493
Location
Near Glasgow
Visit site
When I fitted my Surecal calorifier I specified a 750w element for just this reason. Works fine and also allows the charger to be used at the same time.
 

robertj

Active member
Joined
13 May 2007
Messages
7,313
Visit site
Not quite, because the alternator is still an inductor, so the overall circuit has some inductance hence the power factor will not be unity even with a purely resistive external load. Not a very efficient way to heat water, and I would suggest a max of 750w on a 900w max output genny is more prudent.

It is a 1000w maximum but 900w continuously rated the Honda EU 10i
 

Alan S

Well-known member
Joined
5 Jun 2016
Messages
632
Visit site
Not quite, because the alternator is still an inductor, so the overall circuit has some inductance hence the power factor will not be unity even with a purely resistive external load. Not a very efficient way to heat water, and I would suggest a max of 750w on a 900w max output genny is more prudent.

Pedantic I know, but with a 900W resistive load the Voltage (230V) and current (3.5A) at the generator output will be exactly in phase. Power Factor 1, 900W, 900VA.
Still a good idea to de-rate it though.
 

superheat6k

Well-known member
Joined
10 Jan 2012
Messages
6,785
Location
South Coast
Visit site
Pedantic I know, but with a 900W resistive load the Voltage (230V) and current (3.5A) at the generator output will be exactly in phase. Power Factor 1, 900W, 900VA.
Still a good idea to de-rate it though.
The alternator coils are still part of the electrical circuit, so some inductive reactance is present in the overall circuit, therefore some phase shift will be present. This is why generators are rated in kVA (apparent power) rather than kW (true power). The heater here is 900 W, so the generator will have to put out 947 VA at 0.95 Power factor, although the power factor efficiency may vary, without capacitive reactance it will not be 1 or unity.

Thus if it is rated at 900 VA continuous then a 900W heater will exceed this.
 

Alan S

Well-known member
Joined
5 Jun 2016
Messages
632
Visit site
Superheat6k,
Don't understand where you're getting the 0.75 and 0.95 figures for power factor from.
This generator specifies 900W continuous, 230V, 3.5A, no mention of power factor.
The power factor of a resistive load is 1, so Watts are the same as VA.
Apologies to the OP. 750W immersion will be fine, 900 might be pushing it.��
 

superheat6k

Well-known member
Joined
10 Jan 2012
Messages
6,785
Location
South Coast
Visit site
Superheat6k,
Don't understand where you're getting the 0.75 and 0.95 figures for power factor from.
This generator specifies 900W continuous, 230V, 3.5A, no mention of power factor.
The power factor of a resistive load is 1, so Watts are the same as VA.
Apologies to the OP. 750W immersion will be fine, 900 might be pushing it.��
OK 3 phase generators tend to quote 0.8 PF and single phase closer to 1 because generally they will have a resistive external load, but the genny itself is still an inductor. At best you will get 0.95 although I have seen some mention a PF of 0.98

For a better understanding then google True Power v Apparent Power where you will find plenty explanations of power factor in AC circuits, and if your maths isn't too rusty some will even explain exactly why. My own AC theory knowledge is now almost 40 years old so apologies if I don't explain the niceties too precisely, but the principles are still there for me because I deal with 3 phase industrial systems for my day job, and power factor is certainly an issue especially in today's environment of optimum energy efficiency.

I expect it is simpler for makers of small generators to muddy the waters between 1 kVA and 1 kW, but they are not the same, and not many users, if any, of tiny generators are going to understand the concept, let alone accurately measure the output in terms of true or apparent power.

The issue here is that the maximum continuous output is 900W, which correlates with a round down of 1 kVA at 0.95 PF lagging, but most here agree the sensible limit for the actual user is in fact 750W.
 
Top