Home Built Engine Dyno - Page 4 - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Garage - Tools
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #46 (permalink)  
Old 08-03-2013, 12:16 AM
Registered User
 
Join Date: Jul 2013
Posts: 15
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally Posted by Silver Shadow View Post
Should be.
What happens is the speed drops to half, and the rotor becomes a less efficient pump with less ability to pump itself dry through the outlet orifice restriction.
Because you have not changed the incoming water flow, the drum fills up more, and the torque resistance stays the same.

If you keep reducing the rpm and not altering the incoming water flow, the drum fills even more. Once the drum is entirely full of water it cannot fill any more.
At that point the water brake is at its fullest mechanical resistance, and any further reduction in speed would reduce the torque holding ability.

So a small water brake will work fine with high power high rpm engines.
For big torque low rpm engines you need a bigger diameter water brake.
Bike engines are easy to hold, big capacity high boost turbo diesels very difficult.
ok... thanks, i will try to designing now, maybe i will ask questions in the future..thanks for the help
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #47 (permalink)  
Old 08-03-2013, 01:40 AM
Registered User
 
Join Date: Jul 2013
Posts: 15
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
if i want to use water pump for water brake dyno, is it possible for a water pump running at 11000 rpm or higher?
Reply With Quote Quick reply to this message
  #48 (permalink)  
Old 08-03-2013, 05:02 PM
Registered User
 
Last photo:
Join Date: Aug 2008
Location: Melbourne, Australia
Posts: 113
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
Quote:
Originally Posted by dvnfarrell View Post
if i want to use water pump for water brake dyno, is it possible for a water pump running at 11000 rpm or higher?
Problem with any ordinary water pump is that the torque to drive it varies a lot with rpm, which makes controlling it even more of a problem than a proper water brake which is self correcting for changes in rpm.
Reply With Quote Quick reply to this message
  #49 (permalink)  
Old 08-03-2013, 09:23 PM
Registered User
 
Join Date: Jul 2013
Posts: 15
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally Posted by Silver Shadow View Post
Problem with any ordinary water pump is that the torque to drive it varies a lot with rpm, which makes controlling it even more of a problem than a proper water brake which is self correcting for changes in rpm.
oohh..so i should design a water brake dyno with stator and rotor,, right?
Reply With Quote Quick reply to this message
  #50 (permalink)  
Old 08-03-2013, 09:29 PM
Registered User
 
Last photo:
Join Date: Aug 2008
Location: Melbourne, Australia
Posts: 113
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
Yes if you want to do it that way.

Why don't you build an eddy current dyno instead ?
Much easier to control than a water brake.
Reply With Quote Quick reply to this message
  #51 (permalink)  
Old 08-04-2013, 01:19 AM
Registered User
 
Join Date: Jul 2013
Posts: 15
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
i need to run the dyno up to 3 days i think...so i thought water brake dyno will be great because its dissipation to heat.

the second is, i dont know how to design a eddy current one, because its electronic aspect, i am not good enough at that subject..hhaha
Reply With Quote Quick reply to this message
  #52 (permalink)  
Old 08-04-2013, 01:39 AM
Registered User
 
Last photo:
Join Date: Aug 2008
Location: Melbourne, Australia
Posts: 113
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
Water brake of the size you are thinking about can run a total loss water system, so yes that part is pretty easy.

Eddy current machine just needs a big air blower to cool the brake disc.
The advantage is, it offers DIRECT and very fast electrical control of the dyno load, you don't need variable speed pumps or flow control valves which introduce a whole lot of extra control problems and are something extra to go wrong.

I am an electronics guy, and my own home rolling road dyno is eddy current, so my opinion is probably a bit biased.
But that is how I would tackle what you are trying to do if it was my project.
Reply With Quote Quick reply to this message
  #53 (permalink)  
Old 08-04-2013, 02:21 AM
Registered User
 
Join Date: Jul 2013
Posts: 15
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
so can u teach me how to design a eddy current dyno? because i know nothing about that...i am trying to design a water brake now, even though i cant calculate the mechanical aspect correctly...
Reply With Quote Quick reply to this message
  #54 (permalink)  
Old 08-04-2013, 06:42 AM
mercmad63's Avatar
Registered User
 

Last journal entry: An update
Last photo:
Join Date: Jan 2005
Location: Brisbane,Australia.
Age: 57
Posts: 197
Wiki Edits: 0

Thanks: 0
Thanked 2 Times in 2 Posts
Quote:
Originally Posted by dvnfarrell View Post
so can u teach me how to design a eddy current dyno? because i know nothing about that...i am trying to design a water brake now, even though i cant calculate the mechanical aspect correctly...
You are asking a great deal here ,in fact what you asking is what someone would expect to aquire in terms of knowledge over a period of several years at university,with at least 4 years of techincal training in the use of machine tools.
I have all of the above experience as it happens but even so it was still easier to hunt down an unused peice of gear.
Your basic need then is a device to hold a pair of round turbines in a housing,
One is engine driven,one is fixed to the rotor housing .

The housing has to be fed a constant,controllable flow of water .(allow the water to get hot and boil and you will not get a proper braking effect).
This housing must be free to rotate through an arc of 45 degrees.
An arm of 500 mm length must project off the housing so it pulls against a load cell. this cell sends it signal to your PC where you can read off the pressure being exerted on it by the engine.
Add more water,and you are increasing the amount of effort required to turn the engine driven turbine and thus more pressure on the load cell.
Thats what a dyno does.
So, to get around your first task...a turbine. The most effective is the Fluid coupler from a truck or bus which is not a torque convertor. OK,thats a hard one ,but they do exist especially in the UK where trucks such as Leylands,AEC,Foden etc used a preselector type trans and the huge diesel engines produced a lot of torque.Far more than you will ever see from a car engine. A car torque convertor will not work,they are too weak and you don't want a torque multiplier effect.
The actual size or design is not as important as keeping the water flow constant and the temperature down below boiling. And dynos will boil water quickly under load.
The only way to control water temoperature is to use a cooling tower,a Big one!. So start looking around slavage yards etc for air con cooling units which will fit where you want to operate. Pouring water down the drain is not a great idea ,it is expensive and wasteful.
OK ,you got this far and the thought of finding a turbine is too hard... I live where these parts are available and I didn't bother looking too hard...
here is the patent document for the DPX style of dyno. These are actualy very small but can handle huge horsepower,
All you need to do is down load the drawings and dimension the drawings yourself .
Hydraulic brake or dynamometer
The document goes into detail on how it works. Here is one depicted here. Not very big is it? it was sold at Auction in the UK for 95 pounds.

Now, an eddy dyno..if you do not have access to a lot of water , the next best option is get a Truck or Bus retarder. These are mounted on big rigs behind the trans and work on the principle of creating a magnetic flux which the truck attempts to turn .They turn the torque into heat energy but in the case of Dyno,the retarder is connected by an arm to a load test cell ,
Eddy current brake - Wikipedia, the free encyclopedia
Now,you need to be able use a few formulas for calculating just how much force is being transfered to the load test cell (look on ebay for plenty of examples for sale) so if you read this document,on page three are all the formlae you will need.
http://www.sussex.ac.uk/Users/tafb8/...ngOverview.pdf

Last edited by mercmad63; 08-04-2013 at 06:48 AM.
Reply With Quote Quick reply to this message
  #55 (permalink)  
Old 08-04-2013, 08:16 AM
Registered User
 
Join Date: Jul 2013
Posts: 15
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
how should i determine how much debit of water will i use (Q)?
can i know ur email?

i get this formula, T = w * r^2 * p * Q
where T = torque of the shaft (engine)
Reply With Quote Quick reply to this message
  #56 (permalink)  
Old 08-04-2013, 08:17 AM
Registered User
 
Join Date: Jul 2013
Posts: 15
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
how should i determine how much debit of water will i use (Q)?
can i know ur email?

i get this formula, T = w * r^2 * p * Q
where T = torque of the shaft (engine)
w = angular velocity
r = impeller radius
p = density of water
Q = debit

i want to calculate the impeller radius, but i dont know the debit (Q)
Reply With Quote Quick reply to this message

Recent Garage - Tools posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Title for home built hot rod cranky1 Hotrodding Basics 5 10-20-2009 08:51 AM
Home Built and never satisfied. psy4s Introduce Yourself 4 02-02-2008 09:33 PM
Home Built Fuel Injection PsychoBandito Engine 3 08-28-2007 08:06 AM
Home built air compressor OneMoreTime Garage - Tools 5 05-21-2007 06:47 PM
Home Built Stuff Novaman78 Hotrodders' Lounge 20 01-25-2005 05:13 PM


All times are GMT -6. The time now is 08:19 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.