Backyard Aquaponics
A place to discuss aquaponics

We actually test our underground drill rigs in relation to this.

Our rigs have 55KW motors that drive the hydraulic systems, in some circumstances when we are adjusting the main relief on the hydraulic pump we use a tong meter to test the current draw on the electric motor. If we load the hydraulics up too much, which in turn loads the motor and slows it down.... and trips the main breaker.

More load... higher amps...trip!

If we use werdna's claim it would be the other way around.

I think this is coming back to the type of pump. I don't imagine that a hydraulic pump can spin freely like a pond pump, every rotation must pump some fluid, but with an open impeller type pump, like a pond pump, they can spin freely in the water without actually pumping..

Not that I'm pretending to understand this debate to any degree.. I've had electrical engineering friends explain this to me, but I couldn't get it... They told me that if I cut back the valve allowing less flow into my bed that it would actually use less power, I don't see how though...

Im just talking about the motor itself regardless of what is connected to it.

I think that it will make a big difference though, you talked about loading up the hydraulics, a hydraulic pump is very different to an open impeller pump..

Can you borrow the tong and take it home to your AP system?

My understanding is that the guys are saying that load draw on an AC motor is directly related to motor speed. My example was that the hydraulic pump was simply the load to slow the motor down, not so much how or what it is pumping.

Another example would be an electric mixer... your wipping up a cake on the weekend, your eggs and flour are coming along nicely...beaters are spinning qiuckly,... but then you lean over to add some milk and your very manly beard gets caught in the beaters! It jams the beaters and they come to a halt. Now tell me what you think the current draw would be on that motor now? My guess is that the breaker will trip and your whole cake making expadition would come to a hairy end. Sore chin and shattered dreams of ever making it onto masterchef.



p.s. Ill see if I can borrow a tong meter.

Thanks for the valuable background that you have provided on the use of eductors, toefu. I would like to make a few points.


A lot of the positive reviews, etc that I initially read concerning eductors were indeed on various reef and aquaria sites, and now that I think of it, they were mostly dated around 2005-8. I wasn't aware that technology had moved on, at least in those specialised fish keeping fields. That is not to say, however, that there is not a place for eductors in aquaculture and aquaponics. Some members of the forum have already stated that they have been (are?) using them.


I think it more a design characteristic rather than a flaw in AP setups that gravitational flow of water is utilised in many system designs. I agree with you, however, that there is probably little place for eductors on pipes where water returns to the FT via gravity. Pump pressure is required.


I hadn't heard of stream pumps or toy kit impellers but they sound very effective. Note I wasn't proposing that APers all go out and buy an additional pump to increase aeration or water circulation, rather that eductors (which it seems most of us had little knowledge of) be considered because of what they can offer. I was, and still am, greatly impressed by what a relatively simple piece of kit such as an eductor can achieve in the right application. I believe my big concrete tank system is such an application. [url]PLJ's Big Concrete Tank System[/url] I drain through a biofilter using 2m of head but need to pump the filtered water back into the FT. I have pump pressure.
Another possible application of a small eductor, as I see it, is the fairly common case of a system's pump output being greater than what the GBs can handle. Often a tee and valve are plumbed in, with the excess flow being redirected back into the FT or sump for additional aeration. Wouldn't the addition of an eductor at this point likely be of benefit?


The technologies developed by Koi keepers, marine reef aquaria enthusiasts and other niche groups continually amaze me and they certainly seem to lead the way in these areas of application. It is invaluable, in my opinion, to have forum members such as toefu who bridge the gap between different disciplines/areas of interest that may otherwise develop knowledge and expertise in a 'stovepipe' manner.

Im on a roll.... where's Andrew




Ive got the tong meter, I will test this absurd claim on the weekend.

Yeah but that's where the difference is, the beard has caused the mixer to stop completely.. The pump doesn't stop, it keeps spinning but the water just doesn't go anywhere. As I've already said, I really don't understand it myself, so I'm looking forward to seeing your results..

ahh righto, see your point. Im intrigued to see what resuts I get. Mind you if the guys are right Ill probably still be confused..

Your hydraulic pump is a different style of motor.
I am talking about sealed magnet motor used on pond pumps.

I like the way you risk damage to a $50,000 motor just to prove a point though

Test it on your air pump too if it is a diaphragm style.

You will find that when nothing is connected to the outlet, power is at its highest.
When you block the outlet completely with your finger power draw drops

Isn't that basically saying that.... as head increases... due to actual head height.. and restrictions from plumbing....

That it requires more power/energy... due to more load.. to overcome head/restrictive forces???...

Hang on lets get off the hydraulic motor campaign, it was just an example of loading a AC motor.

Your statement was...

DC motors increase power draw with load, ac motors increase power draw with speed.
Increasing load on a dc motor increases current draw, like you are suggesting.
AC motors work differently.
The current draw is directly related to motor speed, so increased load reduces flow, which reduces impellor speed, which reduces draw.

An AC motor is an AC motor regardless of what it is connected to. Your statement is incorrect. I agree with the comment about DC motors but it also applies with AC motors. If you load it up by slowing it down the Amps will rise therefor the power/current draw will rise and so will power consumption. Im not talking about any kind of pump, we were talking about AC motors.

Its that simple.


Just did the test in the shed on a pedestal fan.


Heres the fan





Here is the tong meter on modified extension cord





Here is the reading of 0.1 amps with the fan at full speed.





Here is the reading of 0.3 amps when the fan blades are stalled (with screwdriver)





....yea, that just happened.

Sorry, it depends on the ac motor.

Test your water pump