Thread: Is this a to good to be true deal ??? or am i missing something

I never noticed this before either. On paper it looks to be the best buy in Dust collectors. The difference in price over the 2HP seems to be because the 2HP unit is made in Taiwan. I think a 2 year warranty is fine however.

Does anyone have one of the Hafco DC 7 units and if so, how good are they

Skippy

Skippy, the problem you ( and most of us) face is the exact reason why Bill Bentz started his quest in the first place. eg: for the DIY market, the information to accurately tell the difference with this equipment is just not available. If you read Bill's info, you will see that he ( and others) have tested many brands with 'interesting' results.

After reading his site and looking at various brands ( in australia) you soon realize that there is a difference between units. You will find a 2 and 3hp units with what appears to be the same size bllower casing ( and presumable the same size impellor) with the same size inlet. while on some brands the blower casing and impellor are actually bigger as the motor hp increases. (It appears that as the size of the impellor dia.- usually found on the 'better known brands'- increases so does the price, from what I can decipher) So its a minefield of 'questionable' data. IMO.
One would 'imagine' that a 3hp unit would have better performance than a 2hp (assuming that the motors are rated the same) ???? Not much help, I know.

Remember, starting large single phase ( 2 pole- 2880 rpm) motors 'can' cause your 'lights to dip' so consider what and how you are going to start your machines, on the electrical supply you have. eg: don't start the machines at the exact same time.

Originally Posted by skippy

G'Day again
Following on from my previous thread re new setup, it appears that a 2HP unit or above id the go. I have single phase power o the shed.
I was going to get the carbatec tradesman 2HP 1500 CFM at $649 but having been ispired to look for a 3 HP unit i find that Hare & Forbes do a DC 7 3 HP 2300 CFM double bag job for $594.
This appears to be a huge saving on a bigger horsepower machine with great air flow capabilities.
The only down side is it is a 2 year warranty as opposed to 5 years from carbatec.

Am i missing anything or does this seem a bit good to be true?

More HP does not necessarily mean proportionately more air flow.

The H&F 3HP is rated at 2300 CFM yet it must be relatively poorly designed because the 2HP Carbatec model is rated at 2000 CFM, and the 3HP Carbatec model is rated at 3100 CFM. Admittedly the 2HP Carbatec is twice the price of the 3 HP H&F, but the 2HP Carbatec also uses only 2/3 the power. The power cost differential does add up especially if you use it a lot and because power costs will rise significantly in the future. For example at 25c/kWhr, if you run your DC for 20 hours a week (and you should really run your DC from the moment you start your first dust making activity until you leave your shed) over 12 months a 3HP unit will use about $80 a year more power than a 2HP unit so after 8 years a 2HP has recovered the price differential. Also the Carbatec model comes with 5 micron bags as compared to the 30 micron bags but this won't matter if you locate your DC outside your shed BUT if you do that just be aware that the 3HP unit will usually make a bit more noise than a 2HP unit.

The carbatec models appear to be better value for a long term high use tradie type operator whereas the the H&F models are going to suit a infrequent user.

**** EDIT ***
Actually I just realized my power consumption calculations are err. . . . a bit out . . . . because my calcs assume the DCs operate under a constant full load.

Apart from the first second where it is first turned on a 3 HP DC does not consume anywhere near 2.25 kW unless it is under load, (you can simulate a full load by just closing all your gates).

For example, With clean bags my 1 HP DC draws 3.3A when cI block all my gates, which means it producing 1.06 HP, while my 2HP DC draws about 6A, which makes it a 1.92 HP. When the bags are more than about 1/3rd full the 1HP can draw as much as 4A which means it's drawing considerably more than 1HP.

However when they are not under any load the current being drawn is much less, and depends on things like how dirty the bags are and how long the pipe runs are and how many gates are open. With all gates open and clean bags and short (3m) pipe run the 1HP DC draws around 1.5A and I cannot remember what the 2HP draws, I think it was around 2.5A. As the bags fill up and pipe runs get longer this will increase the load on the DC. So this means if you run your DCs on mainly no load, the power consumption will be less than my calc shown above. The cost modeling becomes a bit more complicated - back to the drawing board.

I have a DC7 and use it quite a lot - most weekends some weekdays. I haven't done a power consumption test on it but I've got a meter here and can do so if anyone is interested. I only run it while the machine I'm using is running, which could be anything from a couple of minutes to an hour or more.

The only niggle I have with it, and this may be common for many dual-bag units, is that one bag fills up quicker than the the other, which means it is really only a 1 3/4 bag unit because you have to empty it as soon as the first bag fills.

Otherwise, it works as advertised.

Originally Posted by silentC

I have a DC7 and use it quite a lot - most weekends some weekdays. I haven't done a power consumption test on it but I've got a meter here and can do so if anyone is interested.

Yep I would be interested in the 4 values, load/no load with full/empty bags.

Thanks

The meter I've got is just an old analogue meter (the one with the spinning disk) that has been hooked up with flex at one end and a power point at the other. It's really only useful if you leave it attached for a period of time, say a week, and see how many kwh it ticks over.

I can get a rough estimate of shorter times by timing the disk, which rotates so many times per kwh. I'll set it up over the weekend and see what comes out. I really need to get a clamp meter, don't I?

(you can simulate a full load by just closing all your gates).
Bobl, Have u got this round the right way?
My understanding is that the power requirement for a fan is greatest when it is moving the most amount of air it is able to...all gates open...when u close all ur gates the fan has no air to move (cavitation) (assuming no air leaks) it produces its highest vacumm but lowest flow...or am I ass about
Peter.

Hey Silent C
Are you happy with the DC7 ? What are you running off it i.e. ducting setup or what and how have you set it up.and how is the noise factor?
I should eliminate the bag problem by making up one of those awesome home made 2nd astge jobbies out of one of those blue barrels. This should catch most of the stuff before it reaches the bags.

Skippy

Quote from BobL
The H&F 3HP is rated at 2300 CFM yet it must be relatively poorly designed because the 2HP Carbatec model is rated at 2000 CFM, and the 3HP Carbatec model is rated at 3100 CFM. Admittedly the 2HP Carbatec is twice the price of the 3 HP H&F,

My point is that it may be a poorer design BUT it still draws 800CFM more than the 2HP Carbatec tradesman and is still 50 bucks cheaper that the tradesman and 500 cheaper that the carbatec 2 bag jobby.
It must be added that i am definitely a weekend wood worrier but i still want to have a decent dust extraction system without selling my first born for it

Skippy

Skippy, yes I'm happy with it. It does what it is supposed to do. At the moment I don't have it connected to ducting, I just have a length of flexible duct that I hook up to the machines. Permanent ducting is on the list and that's why I went for the 3HP. In the long run, I'm planning to make a cyclone and I will use the motor and impeller off the DC7. Noise-wise, I can't really compare to smaller units, not having used one. It's certainly not the loudest thing in my shed though. Outside the shed it's a low hum - probably about the same noise level as my tablesaw.

Haven't had a chance to do any metering yet but I will be using it later in the week so will put the meter on it then.

Originally Posted by pjt

(you can simulate a full load by just closing all your gates).
Bobl, Have u got this round the right way?
My understanding is that the power requirement for a fan is greatest when it is moving the most amount of air it is able to...all gates open...when u close all ur gates the fan has no air to move (cavitation) (assuming no air leaks) it produces its highest vacumm but lowest flow...or am I ass about
Peter.

Nope - You are absolutely correct, fans are funny things. I did the measurements I quoted in my posts above 3 years ago and was very dangerously recalling things from memory.
Just to convince myself I went and remeasured the currents on the 1HP DC.
1) Maximum flow - ie No bags or ducting, motor draws 3.8A
2) Intermediate flow - Clean bag and zero ducting on the 1 HP DC draws 3.3A.
3) No flow (ie entry into the DC blocked with a plastic bag) current drops to 2.8A!
I can't test my 2HP as it is at the milling yard.

Skippy, I agree with your decision, while it won't be an 800 CFM difference in practice, it should still be greater and every bit helps.

Ah havent quite lost it yet, not that I ever had it to lose.
It is surprising how much current a motor uses when nothing is hooked up to it, it's a wonder we can get any work out of them at all...just an observation of mine when I was doing a bit of testing with my DC
Peter

I just checked out my DC7 , the collection bags have about 100 mm of dust in them and the filter bags where recently cleaned . These are the reading i got using a digital clamp meter.
All gates closed 2.2 amps
1 gate open 2.6 amps
2 gates open 2.8 amps
3 gates open 3.2amps

paul , k