Old Sterling inverter and significant voltage drop

[MichaelG]

Hi all,

           I have an old (15 years) Sterling pure sine wave inverter which when I try to use suffers from a significant voltage drop.

I thought the issue was knackered batteries so have fitted three brand new 105AH FLA but the problem persists.

When standing with no load the inverter shows the batteries at 12.7v. When I start the engine the reading goes up to about 14v.

As soon as I put a load on from even a small 250w appliance (a small portable washing machine with no water heater) the voltage immediately drops to around 10v and the inverter shuts down.

Just wondering if anyone could suggest what the problem may be (apart from the decrepit age of the invereter).

 

Many thanks,  Michael.

[Guest]

Are you saying the inverter has a display of the DC input?

If so can you check the voltage at the battery terminals?

Could be a poor connection between inverter and batteries in which case the batteries would show a much higher voltage than the 10V on load shown by the inverter.

[Tracy D'arth]

Put a meter on the battery terminals and watch it as you load the inverter. If it stays well up, you have bad wiring to the inverter. If it drops you have bad battery connections or batteries or the inverter is drawing seriously too much current.

[TheBiscuits]

Switch off the immersion heater ...

[Alan de Enfield]

5 minutes ago, TheBiscuits said:

Switch off the immersion heater ...

 

You just cannot let it drop can you - every opportunity you have to remind me .........................

[MtB]

43 minutes ago, Alan de Enfield said:

 

You just cannot let it drop can you - every opportunity you have to remind me .........................

 

 

What happened then???!!

 

Can someone explain??? 

 

[MichaelG]

Hi Tracy and floating male and thankyou for the advice.

I have checked the voltage at the batteries with a meter and with the engine running the voltage stays up around 14v whilst the voltage shown on the inverter display immediately drops to around 10v as soon as the load is switched on.

 

[Tony Brooks]

I would suggest clean the battery posts and the terminals to bright metal, dress with Vaseline and that might cure your problem. Do the same for the connections to the inverter. Then extend a lead on a multi-meter set to volts with one end on battery lead post positive and the other on the positive stud on the inverter. Apply the load and note the voltage reading. Do the same negative to negative. I would like to think neither reading would be more than 0.5V. The higher the voltage the greater the resistance in the connections and cables between battery and inverter. Without more info the cables could be well undersized when you see what the far eastern vendors supply. You last post more or less confirms a supply cable/connection problem.

Edited April 18, 2022 by Tony Brooks

[MichaelG]

Hi Tony, thank you for the advice. The voltage showing at the battery terminals and at the inverter end of the supply cables are the same. I have tried to remove the cables where they connect into the inverter to examine and clean the connections. They are fixed with alum key bolts which are so corroded they sheered off. Im guessing the terminals under will be in an equally poor state if I can get the cables off without destroying the inverter connections.

[Tony Brooks]

21 minutes ago, MichaelG said:

Hi Tony, thank you for the advice. The voltage showing at the battery terminals and at the inverter end of the supply cables are the same. I have tried to remove the cables where they connect into the inverter to examine and clean the connections. They are fixed with alum key bolts which are so corroded they sheered off. Im guessing the terminals under will be in an equally poor state if I can get the cables off without destroying the inverter connections.

 

I think that you may well be right about corroded terminals. Best of luck.

[MichaelG]

Hi all,

          just a quick update and a thank you for the advice that assisted me in locating the problem. I found that the negative cable from the battery bank at the inverter terminal was quite corroded causing a poor connection. An hour or so of gentle pursuasion and some WD40 managed to separate the two, luckily without damaging either. A clean up with a wire brush and some vaseline and it's all up and working again. Thanks again for the advice.

 

Regards,

 

Michael.

[Tracy D'arth]

Super!  Glad it was an easy fix.  Send us the money you have saved!