Can one motor controller run four fan motors in Paralell?

Hello,

I have four 18A 12V fans that I want to control in unison, and If it is possible, I would like to use one motor controller for all four fans. The controller I have been looking at is a 12-24V 200A brushless and sensorless controller from Kelly Controls with a 100A constant current limit (four 18A fans would have a constant current of 72A).

Here's a link to the controller:
http://www.kellycontroller.com/ksl2420012v-24v200asensorless-bldc-controller-p-654.html

Here's a link for the fans:
http://www.ffdynamics.com/FFD3600B.html


Do you think this would work?

If four fans in paralell is too much would two fans in paralell work?

Thanks!

#1. That is a brushless motor controller, unless the motors are mechanically locked in-time, it can only power a single motor (with reliable starting).
#2. Those are brushed motors on the fans. A brushless controller can not drive brushed motors.
#3. If you are looking to try to generate useful lift with those fans at 12v 18amps, you can forget about it, all 4 together will be under 5lbs of thrust.
#4. Some RC motor/prop combos and produce 20-35lbs of thrust each, but require ~7,000-15,000watts to do it. To put that in perspective, at that same listed 12v of those radiator cooling fans, they would be pulling 580-1250amps each.

LFP is right about the controller incompatibility.

Also, I think you're going to need more lift power than those four fans can deliver. Presumably this is for a hovercraft of some kind. If so, then you can work out the lift power requirement fairly easily. It depends primarily on the cross sectional area of the hover gap (the gap all around the skirt where cushion air escapes) and the static pressure needed under the hull (which depends on the hull effective area and the total all up weight). There's an on-line calculator that will give you some base numbers to work with here: http://www.hoverhawk.com/lcalc.html

Generally, most hovercraft run with cushion pressures around the 0.06 to 0.08 lbs/in² range. The hover gap can be quite small with a decent skirt, maybe an inch or so. If you're looking at a one-man hovercraft of typical area and weight then it's going to need a couple of hp of input power to hover on smooth ground (assuming it has a decent skirt). Those fans probably may not deliver enough static pressure before the blades stall and four of them almost certainly wont be enough, you might get away with 6 or 8 of them at a pinch, depending on the blade characteristics.

You would be much, much better off getting a proper industrial fan (they aren't massively expensive) and driving it with a fairly big motor, maybe a couple of kW at the right speed. Getting enough battery power at a reasonable weight will be the next challenge, unless you go for a hybrid system.

Tiberius on this forum is a serious hovernaut and has looked at using electric lift systems, so he may be able to add some detail to the rough outline I've given.

Jeremy

If you got a speed controller for brushed motors it shouldn't care how many motors are connected - as long as they don't exceed its amperage rating. Those don't need to synchronize with the motor(s) they use PWM to simulate a lower voltage.

5 pounds thrust is probably too much - thats about the potential if they were designed to be ducted-fan thrusters. 9 pounds * ((HP*Diameter_ft)^2/3). But even if they put out 4 pounds thats pretty darn good for 1/3 HP without transmission losses. To push something swamp-airboat style?

In fans, static pressure/vacuum is usually spec'd as inches of water. 27.7 inches = 1PSI. They use that to denote the resistance of ductwork, filters and the like. The 0.08 PSI converts to 2.2 inches which is way off the chart for axial fans. They might push 1/100 of their rated CFM thru that much resistance. If you put them in parallel you get 4 x 1/100but if you put them in series (not electrical series but one fan blowing into the back of the next) then it acts, almost, like one fan with more HP and could get you 16/100 instead of 4/100.

If they don't give you a chart showing how much airflow at different static pressures(SP), then its not made to handle much pressure at all. I have a 1hp squirrel-cage type blower that can push 1700 CFM @ 1.7 inches. You'd need around 3-4 HP to blow 3600 CFM @2.2 inches SP.

Samba said:

5 pounds thrust is probably too much - thats about the potential if they were designed to be ducted-fan thrusters. 9 pounds * ((HP*Diameter_ft)^2/3). But even if they put out 4 pounds thats pretty darn good for 1/3 HP without transmission losses. To push something swamp-airboat style?

In fans, static pressure/vacuum is usually spec'd as inches of water. 27.7 inches = 1PSI. They use that to denote the resistance of ductwork, filters and the like. The 0.08 PSI converts to 2.2 inches which is way off the chart for axial fans. They might push 1/100 of their rated CFM thru that much resistance. If you put them in parallel you get 4 x 1/100but if you put them in series (not electrical series but one fan blowing into the back of the next) then it acts, almost, like one fan with more HP and could get you 16/100 instead of 4/100.

If they don't give you a chart showing how much airflow at different static pressures(SP), then its not made to handle much pressure at all. I have a 1hp squirrel-cage type blower that can push 1700 CFM @ 1.7 inches. You'd need around 3-4 HP to blow 3600 CFM @2.2 inches SP.

Click to expand...

The vast majority of hovercraft use axial flow fans for lift, despite the apparent issue with the static pressure being higher than would normally be the case when used in ventilation applications.

You have to start thinking differently when trying to size fans for hovercraft, because they will nearly always be operating well off the normally published curves, with massively variable loadings to add to the problem. Nevertheless, standard, off-the-shelf, industrial fans work extremely well as lift fans, albeit running at pitches that are often much finer, and with pressure ratios that are much higher, than normal.

The most popular fans used by the DIY hovercraft people are the Multiwing/Hascon WIng, adjustable blade type fans. The majority of racing hovercraft seem to use fans of this type, with great success. Off the top of my head I can't think of any current leisure-type hovercraft that use centrifugal lift fans, despite the apparent advantages in terms of the broader, flatter, operating curve. This may well have more to do with practical aspects such as availability and the difficulty in fitting centrifugal fans in a small craft as anything else.

Jeremy

What do those racer guys run? I'd think all 2strokes to keep things very light right?

vanilla ice said:

What do those racer guys run? I'd think all 2strokes to keep things very light right?

Click to expand...

Yes, they fastest craft are pretty much all running highly tuned two strokes, often Rotax units like those used in microlights/ultralights, personal watercraft, and snomobiles.

Tiberius (Nick) on here is a hovercraft racer, so could give a better statement on the current state of the art. One thing's for sure, they are bloody fast (and noisy..........).

Jeremy

hoe-kay, take yer best shot why a wankel isn't better than a 2stroke for hoovering.

and i thot there was some discussion on here once on how to run a brushed motor off one phase of a BL controller.

Thanks to everyone who replied, I was not expecting so many substantive answers.

Jeremy Harris said:

vanilla ice said:

What do those racer guys run? I'd think all 2strokes to keep things very light right?

Click to expand...

Yes, they fastest craft are pretty much all running highly tuned two strokes, often Rotax units like those used in microlights/ultralights, personal watercraft, and snomobiles.

Tiberius (Nick) on here is a hovercraft racer, so could give a better statement on the current state of the art. One thing's for sure, they are bloody fast (and noisy..........).

Jeremy

Click to expand...

Two strokes are very fast, but they are very noisy. I have been trying to figure out how to use an electric or hybrid system specifically to reduce noise.

However, both of the hoverboards that I know of for sale today use 4 stroke engines.

http://www.arbortech.com.au/view/airboard-information/



http://www.futurehorizons.net/hoverboard.htm

Samba said:

If you got a speed controller for brushed motors it shouldn't care how many motors are connected - as long as they don't exceed its amperage rating. Those don't need to synchronize with the motor(s) they use PWM to simulate a lower voltage.

5 pounds thrust is probably too much - thats about the potential if they were designed to be ducted-fan thrusters. 9 pounds * ((HP*Diameter_ft)^2/3). But even if they put out 4 pounds thats pretty darn good for 1/3 HP without transmission losses. To push something swamp-airboat style?

In fans, static pressure/vacuum is usually spec'd as inches of water. 27.7 inches = 1PSI. They use that to denote the resistance of ductwork, filters and the like. The 0.08 PSI converts to 2.2 inches which is way off the chart for axial fans. They might push 1/100 of their rated CFM thru that much resistance. If you put them in parallel you get 4 x 1/100but if you put them in series (not electrical series but one fan blowing into the back of the next) then it acts, almost, like one fan with more HP and could get you 16/100 instead of 4/100.

If they don't give you a chart showing how much airflow at different static pressures(SP), then its not made to handle much pressure at all. I have a 1hp squirrel-cage type blower that can push 1700 CFM @ 1.7 inches. You'd need around 3-4 HP to blow 3600 CFM @2.2 inches SP

Click to expand...

This is exactly the information I have been looking for Thanks!

I am still thinking about getting a few of these fans to try them out. I was going to use eight fans back-to back in two stacks for lift, which the manufacturer has rated at 3500 CFM each, or 28,000 CFM total. If these fans only end up putting out 1/16 of their power, than that would only be 4480 CFM...

However, if these fans are brushed motors as opposed to bruhsless (I am still waiting to hear back from the manufacturer), than I could run all eight fans off this controller:

HDC2450 - Dual 150A, Brushed DC Motor Controller (80A continuous power each channel)

http://www.roboteq.com/brushed-dc-m...50-dual-150a-brushed-dc-motor-controller.html

Toorbough ULL-Zeveigh said:

hoe-kay, take yer best shot why a wankel isn't better than a 2stroke for hoovering.

and i thot there was some discussion on here once on how to run a brushed motor off one phase of a BL controller.

Click to expand...

Getting off topic a little, do you have a source for these?! I would love to get my hands on one for a series hybrid...

Before you go and spend money, make sure that the fans are suitable. The CFM rating is totally and completely useless for a hover application, as you will be running the fans on a part of their operating curve for which they aren't specced.

What you need to know is whether or not the fans will operate without stall (I'm talking about blade stall here, not motor stall) at the static pressure you will have under the hull.

Your hull area is very small, so you will need a much higher than normal static pressure in the cushion. This makes it more likely that the off-the-shelf, fixed pitch, fan blades you've chosen won't work, or if they do they'll be so far off their curve as to draw a lot of power for very little effective flow.

I'm guessing from those pictures that you are talking about a hull size of maybe 6ft x 3ft, which is tiny for a hovercraft. With a total all up weight of maybe 300lbs and a 1/2" hover gap you will need a cushion static pressure of about 17 lbs/ft² (around 800 Pa), a flow rate of around 56 cu ft per second (3360 CFM or about 1.6 cu m per second), a lift air flow velocity of around 74 ft/second (about 22.5 m/S) and a lift power requirement of about 2,000 watts.

Assuming that those fans would work effectively with that high a static pressure (which I think is extremely unlikely) then you would need at least 10 of them to get the flow rate and pressure you need.

You could get a better result with a single, properly designed, commercial fan blade of around 16" to 18" diameter, driven by a suitable 2 to 3kW electric motor. This would take up much less room, most probably be lighter and would actually fit on to the small platform you want to use.

Whether you could carry enough batteries for more than a few minutes use is the other challenge. You are looking at drawing at least 2000w (more when you factor in propulsion needs). Assuming you actually used 3000 watts (2000 watts for lift, 1000 watts for propulsion) then to run for one hour you need a battery pack that will safely deliver 3000 watt hours. In practice you'll need about 20% more battery capacity than this, to get good battery life, so you will really need about 3,600 watt hours for one hour's use.

If you use LiPo cells (probably the lightest easily available ones) then you you can roughly estimate the weight of the pack from RC LiPo pack weights. A 3600 watt hour pack will weigh somewhere around 24kg (53lbs) so this isn't too bad. If you were to use a high power RC outrunner motor (something like an Turnigy 80-100 here: http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=5142) and a decent RC type controller rated at a 120 to 160A then the motor, controller and battery would weigh in at around 30kg (~66lbs) - probably not much heavier than the four stroke motor and fuel on that board you pictured. You would need a reduction drive to the fan, but a simple toothed belt would do the job efficiently.

Cost will be high. The motor is cheap, around $100 or so. The controller could be a relatively cheap one, too, maybe another $60 (although I'd be inclined to look at a high end controller that might cost three or four times that cost, just for reliability). The fan might be around $100 or so, plus maybe another $40 to $50 for the reduction drive parts. Batteries are going to be the real killer though! 3600 watt hours of cheap RC LiPo is going to set you back somewhere between $1400 and $1600, without factoring in the need for expensive chargers etc. Any other suitable battery technology you choose will probably cost more, and be heavier, so this is really the best option.

Hope this helps.

Jeremy

Jeremy Harris said:

Before you go and spend money, make sure that the fans are suitable. The CFM rating is totally and completely useless for a hover application, as you will be running the fans on a part of their operating curve for which they aren't specced.

What you need to know is whether or not the fans will operate without stall (I'm talking about blade stall here, not motor stall) at the static pressure you will have under the hull.

Your hull area is very small, so you will need a much higher than normal static pressure in the cushion. This makes it more likely that the off-the-shelf, fixed pitch, fan blades you've chosen won't work, or if they do they'll be so far off their curve as to draw a lot of power for very little effective flow.

I'm guessing from those pictures that you are talking about a hull size of maybe 6ft x 3ft, which is tiny for a hovercraft. With a total all up weight of maybe 300lbs and a 1/2" hover gap you will need a cushion static pressure of about 17 lbs/ft² (around 800 Pa), a flow rate of around 56 cu ft per second (3360 CFM or about 1.6 cu m per second), a lift air flow velocity of around 74 ft/second (about 22.5 m/S) and a lift power requirement of about 2,000 watts.

Assuming that those fans would work effectively with that high a static pressure (which I think is extremely unlikely) then you would need at least 10 of them to get the flow rate and pressure you need.

You could get a better result with a single, properly designed, commercial fan blade of around 16" to 18" diameter, driven by a suitable 2 to 3kW electric motor. This would take up much less room, most probably be lighter and would actually fit on to the small platform you want to use.

Click to expand...

Thank you for the post Jeremy, you make some very good points.

The two reasons that I choose the car fans for this application was mainly noise and safety, but they very well may not work at all. I still need to do some number crunching, but you definitely have set me on a much better path... I used the same hover calculator a number of times, but was not paying attention to the static pressure.

As far as noise goes, what do you think would be the least noisy option for a motor and fan?

This has been a pretty fun project, thanks again for your help.

Toorbough ULL-Zeveigh said:

hoe-kay, take yer best shot why a wankel isn't better than a 2stroke for hoovering.

and i thot there was some discussion on here once on how to run a brushed motor off one phase of a BL controller.

Click to expand...

Likely related to wankles SUCKING at everything. Fuel economy, specific output, weight, etc. For example, using a 2-stroke, you can have 8-10hp in a similarly sized fit-in-palm package. And you use MUCH less fuel for the same power output...

And remember that the noise generated by a turbulent air flow goes up as the EIGTH POWER of the velocity...

HoverBoarder said:

Thank you for the post Jeremy, you make some very good points.

The two reasons that I choose the car fans for this application was mainly noise and safety, but they very well may not work at all. I still need to do some number crunching, but you definitely have set me on a much better path... I used the same hover calculator a number of times, but was not paying attention to the static pressure.

As far as noise goes, what do you think would be the least noisy option for a motor and fan?

This has been a pretty fun project, thanks again for your help.

Click to expand...

You can pretty much forget about the motor as a noise source, as the fan noise will dominate by a large margin. The key factor governing fan noise is the tip speed, a function of diameter and rpm. You can play a few tunes with combinations of rpm, diameter, number of blades and pitch to get the same flow rate and pressure rise, but there will be some compromises forced on you by the size of the platform. In general, you want to aim for the slowest rpm fan that will give you the required pressure rise and flow rate, as that will generally be the quietest. Fans with more blades are less efficient (because there are greater wetted area viscous drag losses), but can reduce noise, or shift the noise frequency up to a less objectionable range.

Your best way forward would be to seek help and guidance on one of the hovercraft forums. The UK has a hover club, the Hover Club of Great Britain, with a useful forum. There are a handful of technical gurus on there that could talk you through fan choice. Here's a link: http://www.hovercraft.org.uk/vbforum.php Unfortunately they've taken a decision to ban non-members from the technical areas of the forum (a pretty stupid thing to do, in my opinion, as an ex-member of the HCGB) but a post in the general area should get a response. You may get one or two yahoos poke fun at your ideas, but ignore them - they have a few very narrow-minded plonkers who can't accept anything novel.

There are probably hovercraft fora in other countries, too, I've been away from the hover scene for a while so have lost touch a bit.

Jeremy