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Author Topic: Inverter question - Resistive loads  (Read 638 times)

veggie

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Inverter question - Resistive loads
« on: January 15, 2020, 04:59:45 PM »

Can I run an emersion heater from an inverter? or is this bad for the FET's ?
I have a DC system with a small diesel to keep it charged and it can run when loads are applied also.
The DC alternator is rated 140 amps and should be able to keep up to a 1.5kw drain.
How do mod-sine wave and pure sine wave inverters react to resistive loads.?
In this case, a 4KW, 120 volt inverter and a 1.5 kw, 120 volt heating element.

- 6/1 GM90 Listeroid - Delco 33si Alternator
- Changfa R175 - Lease/Neville Alternator
- Kubota Z482 - 4kw
- JiangDong R165 Air cooled - 2 kw

LowGear

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Re: Inverter question - Resistive loads
« Reply #1 on: January 15, 2020, 05:04:14 PM »
What an interesting question.  We're grid tied so from 9:00 AM to 3:00 PM I would think our SMA 6 KW 240 volt inverter carries our electric hot water tank most days.  Ignorance can be a beautiful thing.
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Hugh Conway

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Re: Inverter question - Resistive loads
« Reply #2 on: January 15, 2020, 06:18:43 PM »
Veggie: I have run a heat gun, mu wife using an electric iron for a few minutes using my battery bank and inverter (24V, 4000W) The inverter complains.
With the 6/1 turning the PMG (120/240V), and powering the heat gun, or an electric heater, it is fine
Cheers
Hugh
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mike90045

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Re: Inverter question - Resistive loads
« Reply #3 on: January 16, 2020, 03:50:02 AM »
Just because an alternator is rated at 140A, does not mean it's spinning at the right speed to generate 140A.

But yes, a immersion heater is a purely resistive load, and should not pose any problems for a mod sine or pure sine inverter, rated to deliver 130% of the load.
If your heater is 1500w, you inverter should be spec'd to about 2,000 w so it is less likely to over heat.
1500w is 125A, so that's a beefy load, and your battery/inverter cables need to be able to carry it without resistive losses.

glort

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Re: Inverter question - Resistive loads
« Reply #4 on: January 16, 2020, 06:36:10 AM »

Resistive loads are the easiest, gentlest loads you can have.  Anything will drive them happily. It's inductive and switching loads that pose the challenges.

A 140 A Alt should be able to drive the 1.5 Kw heater, I presume you mean 12V, but the question I would ask is how many HP is the engine Driving it?  If it's a standard car alt, they are pretty inefficient. The design of the claw pole is good, The regulation is lousy. My 6/1 doesn't have a lot left turning 2x 80A alts and I have seen similar results with other engines.

Played around with a lot of Mitsubishi internal fan alts and have Huge respect for them.  You can run the things flat out all day and they just don't care.  They get very warm but are stable and I have found them all to kick out marginally more power than they are rated for.
Car alts have it very easy with stationary Generation as they are operating in ambient temps not near boiling or above as often the case in the engine compartment of a vehicle. This is why the regulation is Crap. It's very tough but also cheap and inefficient.
 
I don't know what the min RPM they have to be driven at but driving them off the flywheels of the  6/1 allows them to deliver full power.
The pulley on them is about 2" so some intelligent person here can probably work out what their shaft RPM is.

On the car they come from they are only driven about 2.5X engine speed so I would think 5000 RPM would be plenty. Also should be remembered the lower the voltage, the lower speed the alt can cut in.

The comment about the cables is also Valid at those power levels. I have just been harvesting some battery cables from cars which I use for things like this.  It's best to Keep the DC cables short as possible and the AC can be longer.  AC is 10X less amps than the DC side in this case. 

I'd Like to find myself a good Leece Nevile alternator and put an external regulator on that.  Gen heads are hard to get here and I'm thinking this may be a good alternative.  Not a cheap one but has benefits none the less.

veggie

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Re: Inverter question - Resistive loads
« Reply #5 on: January 17, 2020, 01:25:09 AM »
Just because an alternator is rated at 140A, does not mean it's spinning at the right speed to generate 140A.


Thanks, I am aware of that Mike90045.
It's a Leese Neville.
I have the factory performance curve showing speed vs. output vs. required HP.
Alternator speed and output are mapped to the engine speed and output.
It can make 120 amps if needed.

------------

Glort: "Resistive loads are the easiest, gentlest loads you can have.  Anything will drive them happily. It's inductive and switching loads that pose the challenges. "

That's good to know about the resistive loads. Thanks.
Flywheel diameter and alternator pulley have all been worked out back when the unit was built.


« Last Edit: January 17, 2020, 07:32:21 PM by veggie »
- 6/1 GM90 Listeroid - Delco 33si Alternator
- Changfa R175 - Lease/Neville Alternator
- Kubota Z482 - 4kw
- JiangDong R165 Air cooled - 2 kw

glort

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Re: Inverter question - Resistive loads
« Reply #6 on: January 17, 2020, 04:53:13 AM »

You certainly have the right alt.
Do you have an external controller and are you running it at 12v or 24?
Looks like a nice setup.

veggie

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Re: Inverter question - Resistive loads
« Reply #7 on: January 17, 2020, 07:30:45 PM »

You certainly have the right alt.
Do you have an external controller and are you running it at 12v or 24?
Looks like a nice setup.

This battery system is a small 400aH 12 volt bank.
At the moment I use the stock internal regulator for bulk charging and let solar do the float charging.
Certainly not as good as a Balmar external 3 step regulator or something like that.
I have not been able to find an external multi step regulator for under $300.
And when converted, that is over $400 Canadian.  :o

Has anyone seen a decent chinese external regulator?


« Last Edit: January 17, 2020, 07:33:55 PM by veggie »
- 6/1 GM90 Listeroid - Delco 33si Alternator
- Changfa R175 - Lease/Neville Alternator
- Kubota Z482 - 4kw
- JiangDong R165 Air cooled - 2 kw

mike90045

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Re: Inverter question - Resistive loads
« Reply #8 on: January 18, 2020, 02:24:12 AM »
Charging from a generator, you don't need 3 stage (or 2 stage) unless you are running unattended for long times. Set your bulk voltage and when the amps start to drop, you have started Absorb, for as long as you like.