Tramp HV Inrush Voltage Protection

By January 25, 2017Uncategorized

Overview

The ImmersionRC Tramp HV was released in late 2016, and has proven to be a solid performer in the FPV market.

As with any product release, we monitor carefully reports of failures, and with the help of our repair centers, dig down to find the root cause of these failures.

By far the most common failure mode for the Tramp HV to date has been voltage regulator damage due to voltage spikes on the battery wires at startup.

Looking carefully at the types of systems which cause this damage, we find a common factor, the use of cheap ceramic capacitors to filter the battery voltage input of ESCs and PDBs.
These ‘Low ESR’ ceramic capacitors, combined with the inductance of battery wires, create voltage spikes at battery connection which can easily reach 2x the battery voltage, and can damage not only the Tramp HV, but any other electronics connected to the battery wires.

The Fix

For the next batch of Tramp HVs, which will ship early February, we have protected the input with a ‘TVS’, a Transient Voltage Suppressor. These are commonly used in automotive applications where power rails can be quite noisy.

This is a minor revision to the Tramp, which will be sold under the same model number as the current product.

The Workaround

For customers who currently own Tramp HVs, are using ESCs and/or PDBs which use ceramic capacitors on the battery side (Kiss-24A, Little Bee 4-in-1, to name just two), and would like to ensure that their product is not damaged, we have a simple workaround, which costs a few cents to implement. This will work not only with the Tramp HV, but any direct LiPo-powered video transmitters, and will not affect Tx performance.

A series resistor, 0.47 ohms, 1W, may be wired in series with the TrampHV power supply. This will ‘dampen’ these damaging power-on voltage spikes, and protect the TrampHV.

The part that we are using ourselves, is a WP1S-R47JA5, but most products with the same specs will work.

Note that if you are running ESCs and/or PDBs which use tantalum, or electrolytic capacitors, or you have added extra filtering yourself using either of these types of capacitor, there is no need to worry, no changes required.
(See end of this document for an aid to identify capacitors)

The resistor may be sourced in most electronics stores, with the following part numbers:
Farnell, part number: 2340789
DigiKey, RSF1JTR470TR-ND (equivalent part)

Installation

Installation is simple, and requires only basic soldering skills.

Cut the legs of the resistor so that ~2mm is left exposed. Cut the positive wire of the cable powering the Tramp HV, tin the ends of the wire, and solder together as shown below.

Be sure to apply some heat-shrink to protect connections from short circuiting.

Identifying Capacitors

Ceramic

These capacitors, on the battery side of ESCs, and PDBs are the source of the voltage spike problems. If your ESCs use several of these on the battery side, it is recommended to protect the Tramp HV as discussed in this document.

ceramic

Tantalum

These capacitors, as used on the EzESC 12A, 16A, and 20A, and many other ESCs, are fine, and should cause no problems. No need for any protection.

caps2

Electrolytic

These are quite common on larger ESCs, and also pose no voltage spike problems at power-up. No need for any protection.

ELECTROLYTIC

An Illustration of the problem

This oscilloscope capture shows an example of the inrush voltage problem.

This was captured on the battery terminals of a ‘Little Bee 4-in-1’, as a 4s battery was attached.

Note the size of the first ‘ring’, which peaks at close to 26V, much higher than the battery voltage of 16.8V. 

Depending upon the internal resistance of the battery, cable lengths, etc. this effect can be far worse, and can easily destroy attached electronics.

Repairs and Support

As with any ImmersionRC product, our network of support and repair centers is always there to help. A quick email to repairs@immersionrc.com starts the process.

If you have TrampHVs which have been damaged by inrush voltage, please contact them and they will arrange for a repair or replacement.

If you wish for help with the modification described in this post, they can also give advice, and supply parts if necessary.