Motor Capacitors Australia

If your pump hums but won't turn, a capacitor is the most likely culprit and the cheapest thing to rule out. This page lists the replacement start and run capacitors we stock for water pumps — the sizes that fail on pool pumps, pressure pumps and bore pumps around the country, with prices on the screen. The guide below shows you how to work out exactly which one you need.

Start by Reading Your Old Capacitor

This is the whole job. Nearly everything you need is printed on the side of the part already in your pump.

You are looking for two numbers.

The capacitance, written in uF (microfarads). It might show as a single number like 30uF, or as a range like 88-108uF. Which of those you have tells you a lot, and we will come back to it.

The voltage, written as VAC. On pump capacitors this is almost always 250, 330 or 450.

Match the uF value. Go up on voltage if you need to, never down. A 450 VAC capacitor will safely replace a 370 VAC one of the same uF. The reverse will fail, sometimes violently.

Also measure the body before you order. Diameter and height vary between brands even at the same rating, and the new one has to fit the housing or the clamp. Take a photo of the label while you are there. If the print has burnt off or the case has bulged, call us on (08) 6384 5884 with your pump make and model and we will look up the original spec.

Start Capacitors and Run Capacitors Are Not the Same Part

People get caught by this constantly. They look similar and they are not interchangeable.

Run Capacitors

A run capacitor stays in the circuit the whole time the motor is turning. It smooths the current and keeps the motor efficient. Because it works continuously, it has to survive constant heat and constant voltage.

You can spot one by the label. Run capacitors carry a single uF value and a high voltage rating. Ours are 450 VAC and come in 7, 9, 12, 15, 16, 20, 25, 30, 35, 40, 45, 50 and 100uF.

These are usually the oval or round metal-cased type. Get the value right. If a run capacitor is even a few uF off, the motor draws more current than it should and runs hot, which shortens its life even though the pump appears to work.

Start Capacitors

A start capacitor is only in the circuit for the first second or two. Its job is to give the motor the kick it needs to break away from standstill, then a centrifugal switch or relay drops it out.

You can spot one by the label too. Start capacitors carry a range rather than a single number, like 43-53uF or 216-259uF, and a lower voltage rating. Ours are 250 VAC and 330 VAC, in ranges from 21-25uF right up to 340-408uF.

These are the black plastic cased type. The range is normal and not a sign of a cheap part. Start capacitors are electrolytic, and electrolytics are manufactured to a wider tolerance because they are only energised briefly. Pick the range that contains the value your pump calls for.

Some pumps use both. If yours has two capacitors, replace like for like and don't swap their positions.

Before You Buy, Check the Capacitor Is Actually the Fault

A capacitor is cheap, so it is worth ruling out first. But it is not always the answer, and we would rather you didn't buy the wrong thing.

Points to a failed capacitor: the motor hums but the shaft doesn't spin. It starts if you give the impeller a nudge. It trips the breaker on start-up but runs fine once going. It starts fine cold and refuses when hot. The capacitor case has swollen, split, or leaked an oily residue.

Points to something else: the motor spins freely but moves no water, which usually means it has lost prime or the impeller is blocked. Total silence with no hum, which is more likely a power supply, thermal overload or switch problem. Water in the terminal box, which means the fault is upstream of the capacitor and needs sorting first or the new part will fail too.

If the pump is controlled by a pressure switch or controller, the fault may sit there instead. Have a look at our pump controllers and pressure control components ranges.

Why Capacitors Fail Early in Australia

Heat is the main killer, and it is worse here than most places.

A capacitor sitting in a sealed plastic pump cover on a north-facing wall in February is running well above ambient. Every ten degrees above its rated temperature roughly halves its life. That is why pool pump capacitors tend to go in late summer and why the same part lasts years longer on a shaded pump.

Short cycling is the second cause. A pump that starts and stops every thirty seconds puts far more stress on a start capacitor than one that runs for ten minutes straight. If you are replacing capacitors more than about every couple of years, the real problem is usually a waterlogged pressure tank or a badly set pressure switch making the pump cycle. Our pressure tanks range covers the fix, and a failing float switch can cause the same cycling on a tank or sump setup.

Voltage swing is the third, and it hits rural and regional properties hardest. Long supply runs and generator power both push capacitors outside their comfort zone.

Two practical things help. Improve airflow around the motor if you can, and fit a capacitor rated at or above the original voltage rather than at the minimum.

Fitting It Safely

A capacitor can hold a dangerous charge after the power is switched off. It does not need to be connected to anything to hurt you.

Isolate the pump at the switchboard before you go near it. Treat the terminals as live even once the power is off.

If the pump is hardwired rather than plugged in, get a licensed electrician. That is the law in every Australian state, and it is also the sensible call. If you are at all unsure which wire goes where, take a photo before you disconnect anything and ring us before you start.

Buying Motor Capacitors From Pumptastic

We are a Western Australian pump supplier based at 7 Hampton St, Greenfields WA 6210, and we ship Australia-wide. Shipping is free on orders over $100, and the terms are on our delivery and shipping page.

The reason most people order here is that the prices are listed. You can see what a 30uF 450 VAC run capacitor costs without filling in a form or waiting on a callback. When your pool pump has stopped in the middle of summer, that matters.

We stock capacitors that suit a wide range of pumps, including Davey, Onga and Grundfos units, along with the pool pumps and bore pumps we sell. For seals, impellers and other wear items, see our spare parts range.

If you cannot read the old label, or you want us to confirm the size before you order, get in touch or call (08) 6384 5884 with the make and model of your pump. It takes a couple of minutes and it saves you buying the wrong part twice.

Frequently Asked Questions

How do I know what size capacitor my pump needs?

Read the label on the existing one. It will show a uF value and a voltage rating. Match the uF exactly and match or exceed the voltage. If the label is unreadable, call us with your pump make and model and we will look up the original specification.

What is the difference between a start and a run capacitor?

A start capacitor only works for the first second or two to get the motor turning, and is labelled with a uF range like 88-108uF at 250 or 330 VAC. A run capacitor stays in circuit the whole time the motor runs, and is labelled with a single value like 30uF at 450 VAC. They are not interchangeable.

Why does my start capacitor show a range instead of one number?

Start capacitors are electrolytic and are made to a wider tolerance, because they are only energised briefly. The range is normal. Choose the range that includes the value your pump requires.

Can I fit a capacitor with a higher voltage rating?

Yes. Going up on voltage is safe as long as the uF value is the same. A 450 VAC capacitor will replace a 370 VAC one of the same capacitance. Going down on voltage is not safe and the capacitor will fail early.

Can I use a slightly different uF value if the exact size is out of stock?

Not on a run capacitor. Being even a few uF out makes the motor draw more current and run hotter, which shortens its life. On a start capacitor you have a little more room, since they are already rated as a range, but stay within it. Ring us rather than guessing.

How do I know the capacitor is the problem and not the motor?

The classic sign is a motor that hums but does not spin, and starts if you nudge the impeller. A swollen, split or leaking capacitor case is a certainty. If the motor is completely silent, or spins freely but pumps no water, the fault is probably somewhere else.

How long should a pump capacitor last?

Five to ten years in a well-ventilated installation. Much less in a hot, enclosed pump cover, or where the pump short cycles. If yours are failing every year or two, look at what is making the pump start and stop so often rather than just replacing the part again.

Can I replace a pump capacitor myself?

Capacitors hold a charge after the power is off, so isolate the pump at the switchboard first and treat the terminals as live. If the pump is hardwired rather than plugged in, Australian law requires a licensed electrician. If you are unsure, use one.

Do you have capacitors for pool pumps?

Yes. Pool pumps most often use a single run capacitor in the 20 to 50uF range at 450 VAC, which we stock. Check the label on your unit to confirm, or send us the model number. See the pool pump range if the motor itself is past saving.

Do you ship to regional and remote areas?

Yes, we ship Australia-wide, and shipping is free on orders over $100. Capacitors are small and light, so they post easily. For remote destinations, message us before ordering and we will confirm the delivery window.

Can I get a quote instead of ordering online?

Yes. Call (08) 6384 5884 or use our contact page. Send your pump make and model, or a photo of the old capacitor label, and we will confirm the right part and price.