DISCLAIMER!!!
We (that being my husband Grant, myself, or the FNZAS) TAKE ABSOLUTELY NO RESPONSIBILITY for any problems arising from anyone making their own heatpads using these instructions.
Grant has many years electronic and electrical experience and has a number of electrical qualifications. We suggest you get your finished pad checked and signed off by a registered electrician. Failure to do so will result in your insurance company refusing to pay out in event of fire or damaged caused by the heatpad malfunctioning.
That said, our own heatpad has been running about 10 years with no problems so far.
Materials:
Pinex the same size as the tank base
Silicone covered resistance cable
Thermostat
Map pins or drawing pins
Parcel tape
We originally bought the silicone cable from Argus Heating in Christchurch. The company no longer appears at that address or phone number but there is an Argus Heating at 445 St Asaph St, ph 03 379 5100 so I would assume it is the same company as the man who helped us, Brian Shaw, is still listed as the after hours contact. He was very helpful and helped us work out what we wanted. He will need to know the length of the cable and the power (in watts) you need. I’m sure there are other places selling this cable but this is the one we know.
First thing to decide is the power required to heat the tank. This will be determined by the size of the tank and the lowest room temperature where the tank is situated. In a warm room where the temperature is unlikely to fall below 15˚C, 150 watts for a 60cm tank holding about 100 litres should be adequate. This also depends on whether the tank is insulated. If it is open on all sides then more heating may be required.
Our lounge tank, holding approx. 250 litres, is heated by 300 watts and maintains its temperature well. It is only open to the front.
The length of cable must then be calculated. As the tank is going to sit on the cable, there must be enough cable to support the tank with very little stress.
Calculate the area of the tank by multiplying the length (in cm) by the breadth. Divide the result by 200 and this will give the cable length in metres. None of these measurements is critical.
As there is a large range of cable resistances available (2 – 3000 ohms) there will be a cable suitable for the power and length combination required.
A length of mains flex will be needed to connect to the thermostat. This will be attached by the cable supplier as it needs to be crimped and sealed using heatshrink and glued sleeves for safety. This method ensures the joint will also be waterproof to guard against water splashes. They will make the flex whatever length you require.
The heater is assembled on the Pinex base by arranging it to cover the whole base as evenly as possible to minimise stress on the base of the tank. The joint where the flex is attached will be larger than the cable so cut a depression in the Pinex to lower the joint into. The top of the joint will need to be even with the top of the cable. Diagram shows one suggested pattern to evenly distribute cable.
Use the pins to hold the cable in place on the Pinex while laying it out, ensuring there are no sharp corners in the cable. The parcel tape is then used to keep the cable in place when the pins are removed. Check that the top of the cable is level so there are no high points to stress the bottom of the tank.
The tank can then be placed on the cable. Do not slide the tank when it is placed on the cable as this will roll the cable, possibly stressing it, and cause breaks in the wire.
A separate thermostat is needed to control the heater. Make sure you wire the two together correctly or get a qualified electrician to do it.
After this article appeared in the Aquarium World magazine, we received a letter of complaint from a man who was building his own heatpads and insisting the cable had to be placed in grooves so it was flush with the base as he claimed there would be too much stress on the glass. The tank has been sitting on the pad for about 10 years now and no leaks so far. We have 2 other tanks on similarly built pads with no problems either.
We will add the following though…
1. No DIY is foolproof. Never attempt to make you own electrical equipment unless you have electrical training or experience.
2. As the tank rests directly on the cable in this design ensure the cable is evenly distributed under the tank so there is no part of the tank with a large unsupported area of glass.
3. When placing the tank on the cable be careful not to drag the tank across the cable as this could drag the cable out of position.
4. The thermostat must be rated to handle the load of the heatpad. Commonly available thermostats (not so commonly available these days I don’t think) are rated to a mazimum of 300 watts. Too high a load could cause the thermostat to fail, overheating (or not heating) the water.
5. Always double check your calculations and perhaps get someone else to confirm your answers. Remember even the ‘experts’ can get it wrong.
6. Have you checked your contents or house insurance policy to see if you are covered for damage done by leaking tanks?
