Welcome to this month’s blog, regarding the perils of retrofitting old lighting fittings with new LED driver/lamp/tube kits – we hope this article will help purchasers/installers and specifiers ,make an informed decision when choosing between a retrofit solution ,or using a new product on site.
When considering to convert onsite old AC powered lamps/tubes with a retrofit DC driver+ LED array kit, which re-uses the old fitting and employs the old AC lamp holder as a DC connection to the LEDs –there some important reliability/safety questions to consider before commencing:
Q- What will happen if the user fits another LED lamp/tube product into the altered fitting/lamp holder?
Will the circuit be safe –even when trying many different types of replacement lamp in the converted lamp holder [if an AC lamp/tube is fitted into a converted DC lamp holder by accident– will it cause an energy hazard [overheating/EMC/risk of electric shock]?
If another make/model of LED lamp/tube is used – will it have the same specification/wiring configuration as the previous one [with the same forward voltage/forward current] - or could it be overdriven/overheated –if the driver and LED are not electrically compatible what will happen?
Q- Does the old fitting allow the driver and LEDs to operate at the correct temperatures?
Will the driver and LEDs Ta limits be exceeded inside the fitting? Has thermal testing of the final onsite product been done to prove this?
LED drivers have a Ta rating and Tc and may be intended to be used in open air conditions- if mounted inside a fitting, the combined heat from the LEDs and driver may be trapped inside the fitting [making the fittings internal air temperature up to 10C to 20C higher than the external ambient] in such a case, a product with a maximum Ta of 45C could derate or shut off- if the site ambient temperature was 25C!
Compatibility /future availability
Note: if the retrofitted LED lamp is replaced by one with different electrical characteristics [E.G different forward voltage/current but the same wattage] the driver’s efficiency will alter – this could create additional generated heat from the driver- thus lowering the products external Ta limits even further and possibly causing to fail –or not achieve L70 performance after 50,000Hrs.
If a site requires replacements lamps at a later date – will the lamps still be available on the market?
If there is a problem with the driver’s onsite through no fault of the product [say-due to power quality problems] but the drivers need to be replaced, can replacement drivers be found -if they use a non-standard voltage/current output ? The installer may have to change both lamp and driver!
Lamp holder compatibility
When lower voltages are used on supplies to lamps –higher currents may be expected, swapping a 400W high voltage AC driven lamp with a 200W [ 48V] low voltage lamp will result in an increase of current through the lamp holder [ +high inrush currents could also occur –especially in cold conditions] Is the lamp holder rated/certified to handle this difference?
Where old lamp holders are being re-used, the lamp holder’s plastic could have degraded to point of becoming brittle – where they break apart during lamp installation, in such cases additional/unforeseen installation time/cost may be incurred.
If the lamp holders are brittle – they may not support the weight of the new LED lamps/tubes and could fall out at a later stage [causing injury or risk of electric shock] be aware that there are some non-compliant products about that may exceed the weight handling for the intended lamp holder.
Degraded connections could create intermittent operation and/or additional heat, if the contact area on the lamp holder is reduced –this could then create more problems such as degradation of plastic lamp holder parts.
Running through existing control gear
With plug and play LED tubes – the magnetic control gear is left not bypassed with the LED tube inserted in line- there can be the following issues to consider:
Reduced reliability – the tube will only operate as long as the magnetic gear works – using different makes/models of old/worn control gear of unknown condition/age limits the fittings reliability.
Increased power consumption – loss of energy savings, if the magnetic ballast is in line-or will consume additional power.
Increase in fittings internal temperature – using the magnetic ballast in line will generate more heat inside the fitting – and could alter/lower the fittings Ta rating.
Where fitting use combined emergency lighting – the emergency lighting circuit may operate to a different specification when running a plug and play LED tubes- the light levels and time period may differ- and if the tube is close to the end of its L70 output level -it must still provide the correct emergence light level [or a re-fit would be required]
Where T8 electronic HF ballasts are used in line- ballast/LED driver compatibility could be an issue which can affect reliability .Also, if the original/old HF ballast is worn out –its electrical characteristics may have altered [as capacitors can degrade over time and affect output levels/drive waveform shape and power consumption] this could electrically stress the retrofit driver, and cause additional internal heating – which could reduce the life span of the LED drivers and LEDs
Poor quality connections between old fluorescent HF driver outputs and LED products- if the lamp holders are old/worn and have a poor contact area, high frequency currents running through the connection point can act like a ultrasonic welder – creating great amount of heat on the lamp-holder [potentially leading to melting of the plastic holder –causing the tube to drop out of the fitting along with the melted/exposed connector] we once heard of a bad connection on a HF T5 fittings lamp holder that melted the glass of the T5 tube!
Onsite problems can occur, with products that use a separate DC power supply and LED lamp/tube – such as downlights LED panels/LED tubes, where the driver and LED array/fitting are supplied with an inline DC connector and the installers use hot swapping installation methods:
Hot swapping appears to save time [ at first] the electrician can wire all the drivers to mains in one go ,and then connect the DC outputs to the lamps afterwards [ in one go ] without isolating the power- but there could be a high price to pay ,with extra work/time needed to rectify a problem caused by this practice.
It is often assumed that low voltage connections using SELV supplies are safe to connect/disconnect/handle while the power to the driver is still switched on – as the voltage level is too low to cause an electric shock, While this may be the case, it is always correct/safe practice to isolate the power to a circuit before commencing work- as any 17th edition electrician would know - as there are a number of non -compliant products on the market which could pose a risk under such conditions- and wiring faults and faulty products can also occur from time to time.
As the industry has seen non-complainant/non SELV drivers on the market – falsely labeled SELV, we would always advise not to assume, that all drivers DC outputs are safe to handle when powered on.
Aside from the incorrect presumption that such a practice is always going to be a safe one and that is goes against the electricians 17TH edition training, there is the matter of potential electrical damage to the LED- which will most likely cause big problems [which may result in having to replace the installed fitting] later on.
Note: Just like any other semi-conductor [ like rectifiers]– LEDs have a current inrush when switched on, if we power up a driver [in open circuit conditions] and then connect the LED array, there will be a large current spike going through the LEDs – which can cause damage.
Bear in mind, a driver with no load attached will output its maximum voltage [most probably above the forward voltage rating of the LEDs] - as an example: when a 48V output is connected to a 36V array- the additional charge can exceed the LEDs max, current/ voltage limits and electrically damage the LED [altering its performance/reliability characteristics] when this happens the LED will can fail, but will most likely operate [at the wrong output level]
Sometimes the LEDs look unaffected at first – but after a few days or weeks [or even months] the following signs can occur:
Note: One signature of electrical damage caused be hot swapping is LED color shift – damaged LEDs can alter their forward voltage and color .On a damaged LED tube or panel product - the user may see different colored LEDs/arrays in the product – some go greenish other blue or red and the CRI is lowered- also light output will be reduced and flickering may begin to occur if the LEDs forward voltage has been greatly altered, eventually the LED array may fail open circuit and cease to work at all.
It is the same with fluorescent tubes – hot swapping can cause premature black ending and reduces the tube lifespan.
We understand that in the real world – that on some old sites have old/badly done wiring [with multiple by-passed /confused AC connections] that it may not be possible to find a way to isolate the power feed – however-in such a situation hot swapped drivers/LEDs will still go faulty- ignoring the perils of hot swapping will not make the issues it causes go away –if a site cant isolate its power, the wiring on the site is non-compliant to allow safe maintenance work and has to be fixed.
When site failure occur –the electrician will be asked if they isolated the supply before commencing work [as they are supposed to by health and safety law] if the answer is no – they may be responsible for the incurred reparation costs [as the units were installed in a non-complaint way] .Manufactures do not always place labelilng stating not to hot swap – as they rightfully assume the electrical will isolate the power as per health and safety law.
There are new drivers arriving on the market, which are specially designed to be used with hot swap methods – these are labelled as hot swappable, but use additional circuity [and parts cost] to achieve this – please note: seeing a hot swappable marking on a driver does not change 17th edition safety rules on isolating the supply before commencing work – it is still a vitally important work safety requirement!
It would also be very foolish to assume that any given driver is a hot swappable type – if it is not labelled as such on the driver’s product label.
Remember- hot swapping to save time/money is a false economy that can end up taking twice as much time with additional cost and reputational damage- problems with sustaining onsite light levels/ colour stability/flicker free performance/driver and LED reliability will most likely occur - is it worth the risk ?
While SELV LED drivers are certified to EN6134, it does not mean that any product [driver +LED +fitting] is complaint