Soft Starting My Fridge

[Biggles]

Just when you think you have it all sorted out something else rears its head.

 

My Hurricane heater cuts out instantly when the fridge starts up.

 

12/3000/12 Victron, 1180 ah battery current voltage 12.4v 240v fridge

 

Heater runs fine so does fridge but if the heater is running and the fridge starts up the moment the fridge starts the voltage drops enough to stop the heater in its tracks. It starts up again about 5-10 seconds later.

 

So I'm wondering if a bigger capacitor might help the fridge start. If so how and where would I put it?

 

Or is there a better way of protecting the heater from the voltage drop?

 

 

[nicknorman]

I would suspect that the fridge and heater share a common current path through something that has more resistance than it should. Try supplying the fridge from a dedicated cable with its own fuse, connected direct to the battery isolator. Don't forget that voltage drops occur in both the positive and the negative, so try running a wire direct from the fridge -ve to the battery -ve. I think fixing the voltage drop issue at source is better than "papering over the cracks" with a capacitor.

[Biggles]

The fridge is 240v Nick fed from the inverter which has 2x95mm cables +ve & -ve direct to the battery about 1.2m away. The only interfearance in this line is the 500amp shunt in the neg line and the 400amp fuse in the pos line.

[FadeToScarlet]

I would suspect that the fridge and heater share a common current path through something that has more resistance than it should. Try supplying the fridge from a dedicated cable with its own fuse, connected direct to the battery isolator. Don't forget that voltage drops occur in both the positive and the negative, so try running a wire direct from the fridge -ve to the battery -ve. I think fixing the voltage drop issue at source is better than "papering over the cracks" with a capacitor.

240v fridge, if I've read it right.

[Biggles]

240v fridge, if I've read it right.

 

Wheres my beer. It's nearly 6pm. Photos ready!!

[ditchcrawler]

 

Wheres my beer. It's nearly 6pm. Photos ready!!

That's a good idea, I may "virtually" join you

[Biggles]

James knows what I mean!

 

 

Back to me fridge..........

[Chalky]

From what you say it suggests that the boat battery supply can't provide the current surge caused by the fridge starting at the same time as the heater. Making the fridge soft start may result in it not starting at all. The inverter should contain a capacitor bank on the input to cope with this. Increasing the size of the capacitors in either the inverter or the heater would probably fix it.

[frangar]

The hurricane is fussy.....have you put a return cable from the heater unit as well as the control box?...some models have a neg stud some don't!....what size are your supply cables to the hurricane? And are there many joints etc.....have you used fuses or good quality breakers? eg blue sea or bep. The instructions do suggest wiring the hurricane direct to the batteries bypassing any isolation switches but all the units I installed we wired up via the breaker panels but all the cabling was over specced and all the switches, breakers etc was Blue Sea

 

Have you checked the voltage at the control box when the fridge starts up? You may find an analogue voltmeter shows the momentary drop better than a digital one.

 

 

Cheers

 

Gareth

[Biggles]

From what you say it suggests that the boat battery supply can't provide the current surge caused by the fridge starting at the same time as the heater. Making the fridge soft start may result in it not starting at all. The inverter should contain a capacitor bank on the input to cope with this. Increasing the size of the capacitors in either the inverter or the heater would probably fix it.

 

The inverter does chort a bit when the fridge starts. I was thinking some extra capacitor at the fridge end would take the load off as it would have a charge to dump in on start. I have plenty of battery and well over 12.4v when this happens.

 

The hurricane is fussy.....have you put a return cable from the heater unit as well as the control box?...some models have a neg stud some don't!....what size are your supply cables to the hurricane? And are there many joints etc.....have you used fuses or good quality breakers? eg blue sea or bep. The instructions do suggest wiring the hurricane direct to the batteries bypassing any isolation switches but all the units I installed we wired up via the breaker panels but all the cabling was over specced and all the switches, breakers etc was Blue Sea

 

Have you checked the voltage at the control box when the fridge starts up? You may find an analogue voltmeter shows the momentary drop better than a digital one.

 

 

Cheers

 

Gareth

 

No I haven't checked the voltage but Calcutt say it has a drop out at 11.5v so would assume its that or less. I have the supply going through a 32amp MCB with `pretty heavy cable supplying the consumer unit.

[ditchcrawler]

Don't know if there is any help here http://www.fieldlines.com/index.php?topic=142878.0

or http://www.softstartdirect.com/hfe.php

[nicknorman]

RTFQ! -sorry! But I don't see how adding a capacitor across an AC supply is going to help -surely the opposite if you put it across the supply? If you put it in series to limit the max current, it would have to be huge and of course rated at 400v or so. Then, as said, it might stop the fridge motor starting at all.

 

The DC supply to the inverter seems well sorted so maybe you need to ensure the supply to the heater is optimal. Of course if the voltage at the battery is dipping below 11.5 you mention, the problem would seem insoluble but that is surely unlikely with your largish battery bank.

[smileypete]

As a bit of a 'sanity check'...

 

What is the voltage across the terminals of the heater itself, and across the terminals of the batts themselves, both before and after the mains fridge is running on the inverter - so 4 readings in total?

 

cheers, Pete.

~smpt~

[Biggles]

The problem is not when the fridge is running its when it starts.

 

On the capacitor question, isn't that what motors have capacitors on the outside for? To assist with the start up. I know if the capacitor is duff the motor won't start unless you turn the motor over manually.

[smileypete]

OK I'll try again...

 

What is the actual measured voltage drop between heater terminals and battery terminals when the heater is running?

 

What is the measured voltage at the battery terminals before and after the fridge is running?

 

ETA: ISTR there was a problem with hurricanes in the past with sensitivity to voltage and it needed an inverter/power supply or voltage stabiliser, but I thought the problem was fixed at some point.

 

If you can find out the starting current and running current of the heater that would help get more specific suggestions. Maybe contact the heater manufacturer for their advice on it too?

 

cheers, Pete.

~smpt~

Edited January 12, 2014 by smileypete

[nicknorman]

The problem is not when the fridge is running its when it starts.

 

On the capacitor question, isn't that what motors have capacitors on the outside for? To assist with the start up. I know if the capacitor is duff the motor won't start unless you turn the motor over manually.

The start capacitor is to introduce a phase shift to the start windings so that the (single phase induction) motor starts to spin - otherwise it would not spin. So in summary it is not used to store energy, it is used to introduce a phase shift in the AC supply.

 

It is wired in series with the start winding, thus making it bigger would increase the initial current drain (and alter the phase shift). Making it smaller might reduce the initial current drain but would reduce the starting torque. Fridge motors need a good starting torque because the compressor has to be able to start to run whilst the system is still pressurised.

 

Typically the start capacitor / winding is shut off as the motor approaches its running speed.

 

Therefore there might be some scope for reducing the capacitor value a bit (but of course these types of capacitor are not available in many values) at the risk of the motor failing to start and so overheating. I can't help thinking you would be unlikely to satisfactorily make much difference unless the capacitor, or some other part of the motor, is faulty, and that the solution lies in keeping 12v or so at the heater regardless of the short term inverter load.

 

OK I'll try again...

 

What is the actual measured voltage drop between heater terminals and battery terminals when the heater is running?

 

What is the measured voltage at the battery terminals before and after the fridge is running?

 

cheers, Pete.

~smpt~

Regarding your second point, I think the critical moment is as the fridge starts, not once it is running, therefor OP would have to measure the dip in battery voltage during fridge startup, tricky with a meter since it will only last a second or so, and really a 'scope would be needed. Edited January 12, 2014 by nicknorman

[Biggles]

 

 

Regarding your second point, I think the critical moment is as the fridge starts, not once it is running, therefor OP would have to measure the dip in battery voltage during fridge startup, tricky with a meter since it will only last a second or so, and really a 'scope would be needed.

 

This is so. I will however do some checks, but getting a reading on startup is going to be near impossible for me. I think it safe to say its dropping below 11.5v though

 

Now I understand about the use of a capacitor in a motor. I thought it was there as an energy store to help overcome the start load.

 

I will email Canada in the morning see what they have to say.

 

I

[BEngo]

If the problem is voltage drop at the hurricane, at 12V DC ish, then that is the place to put a capacitor as a local energy store, in parallel with the heater and close to it. So long as the working voltage is high enough to withstand any spikes from inductive components in the heater almost anything should do. An electrolytic will need to be the right polarity though.

 

N

[smileypete]

Regarding your second point, I think the critical moment is as the fridge starts, not once it is running, therefor OP would have to measure the dip in battery voltage during fridge startup, tricky with a meter since it will only last a second or so, and really a 'scope would be needed.

 

I'll try again then,....

 

It's just an initial simple 'sanity check', I haven't heard anything from Biggles (like actual voltage measurements) that rules out a connection and/or batt problem.

 

Not saying it is, but not saying it's impossible either.

 

Often the way to find a problem, is to find ways to prove what ISN'T the problem. Not everybody really 'gets' this.

 

cheers, Pete.

~smpt~

[Keeping Up]

I remember in the past many boats used to run the heater from its own dedicated battery to avoid this problem, by splitting one battery from the bank and using a split charge relay (in addition to whatever was already there)

[Chalky]

If the problem is voltage drop at the hurricane, at 12V DC ish, then that is the place to put a capacitor as a local energy store, in parallel with the heater and close to it. So long as the working voltage is high enough to withstand any spikes from inductive components in the heater almost anything should do. An electrolytic will need to be the right polarity though.

 

N

 

That's exactly the point I was making. What you've got is a short dip in the power supply that's going low enough to cause the micro in the heater to reset. (This is one of the transients that doesn't exist according to certain forum members). Adding a large local capacitor would help overcome the issue. If you do look for something rated above 63V and several 1000uF. Insulate the terminals well - they can give a nasty belt if touched when charged.

 

I'd be talking to the heater supplier - if the device can't handle short transients then it's a marginal design. Common automotive standards are that the device has to be able to stand cold climate cranking which for some engines can be transients causing the battery to drop as low as 3V for several ms. You need some systems to survive this e.g. engine management otherwise you'd never start the engine! The one voltage a 12V automotive / boat supply isn't is 12V.