The Tow Ball Weight Monitor
Can be used with:
The tow ball weight monitor consists of a load cell with 1,5 metres of cable attached. This cable plugs into a receptacle on a plastic box housing an A/D converter. The A/D converter housing is mounted on a wall at the from of the caravan, using the mounting tape provided, in a place where to will not be damaged.
From the A/D converter housing there is a 4 metre cable with a 4-pin XLR plug at its end. The 4-pin XLR plug is inserted into a socket marked 'Tow Ball ' on the control unit. When not in use the load cell may be unplugged from the A/D converter to be stored elsewhere.
On first use the load cell needs to be calibrated to zero even if it already reads '0 Kgs'. To do this connect the load cell to the controller as normal and double tap the Tow Bar button on the mobile's screen. The phone will vibrate briefly and the weight will zero if it was not that already
Using the Tow Bar Weight Load Cell
Measuring the actual weight at the tow bar requires a device that is tall enough to reach the tow hitch under normal use conditions as well as being sufficiently broad-based to be stable.
Measuring the weight on the jockey whee, on the other hand, l could be accomplished with a far smaller sensor, and have the added advantage of being useable while the tow bar was poised over the tow ball immediately prior to hooking on. But there would be a measuring error since the jockey wheel is always closer to the trailer's axle than the tow ball.
For a mobile phone app it is a simple matter to correct for this error as long as the app knows the difference between the distance from tow ball to axle and the distance from the jockey wheel jack screw to the axle. We therefore need to enter this value into the app.
In South Africa the total weight that the trailer tow bar imposes on the tow ball may not exceed 100 Kgs, and my not be less than 25 Kgs. Additionally we are advised that the percentage of gross trailer weight that is supported on the towing vehicle's tow ball should be at least 5% and no more than 7%. It is a simple matter for the app to calculate the percentage of weight that is to be sopported at the tow bar if the app also knows the gross weight of the trailer. So this value must also be entered by the user.
On the right the Tow Bar Weight button shows that the corrected tow bar weight is 106 Kgs (the background colour turns from GREEN to RED when the weight falls outside the 25 - 100 Kg limit). The percentage of tow bar weight to gross weight is shaown at 7%, which is within the accepted boundaries.
The Jockey Wheel Radius vs the Tow Bar Radius
To find the correction factor to be applied to the jockey wheel position we measure the distance from axle to the centre of the tow bar cup (a) as well as distance from middle of the jockey wheel jack screw to centre of the tow bar cup (b).
We then divide (b) by (a) and muliply the resuly by 100
So, if tow bar centre to axle is 4000mm (4 metres) and tow bar centre to the jockey wheel jack screw is 470mm
then 470/4000 = 0,117 and multiplied by 100 = 11,7%
To enter this into the app we tap the Tow Bar button once, and then immediatel double tap the Caravan Pilot Title. The slide control you see at left will appear, and you move the slider until the Reduce number above it reads 11,7% (Max is 20%). To Save tap the Caravan Pilot Title once more. This value will endure until you change it
Enter the Gross Weight of the Trailer
To enter the trailer's gross weight tap the DactyTech logo at screen bottom once and then immediately double tap the Caravan Pilot Title.
The slider seen at right will appear on the mobile's screen. Adjust the slider until the Gross Wt figure matches that of the trailer.
To Save tap the Caravan Pilot Title once more.
Weighing the Jockey Wheel
The load cell can be placed under the jockey wheel jack screw, or under the axle or even the wheel itself if nothing else is available. For best accuracy the point at which the jockey wheel assembly rests on the load cell should be the same distance back from the tow bar cup as was used in the calcuation above. If measuring under the wheel or the axle these should be turned to reflect the same radial distance from the tow bar as your measurement.
Allow a few seconds for the messaging between the conrol unit and the phone to complete. If there is a significant deviation from the desired nose weight you can now enter the caravan, phone in hand, and relocate weight until you are satisfied. Remember to stand over the axle to eliminate your own weight from the equation.
Load cell for measuring tow ball weight R500
Shipping is usually together with a control unit, which is free.