HiFi buzz when running off inverter - any electrical whizzes on here?

[Tony Brooks]

29 minutes ago, Woodfern said:

Thanks all for the helpful diagnosis and advice. I think I will probably end up replacing the inverter/charger with separates as the inverter part can't be turned off according to the manual.

 

If I do this, would it still be possible for the inverter to be bypassed when the Travelpower is on?

 

That depends upon the type of inverter you buy. Some (expensive ones) will pass any external 240V AC through them and only invert if the load is more than the external supply rating. The simplest way would be a break before make source selector switch or a relay can be used to do a similar thing. Do a forum search, we have covered it before.

[cuthound]

Late to the party on this but here are my thoughts.

 

Won't be an earth loop. They always cause a 50 Hz audible hum, assuming the hi fi is mains powered, which is never high pitched.

 

I agree it is likely that the inverter is of the modified sine wave type, some are little better than squares wave output,  and as such will produce a wide range of harmonics,  which will materialise as noise from the speakers of a hi fi system.

[Woodfern]

17 minutes ago, Tony Brooks said:

 

That depends upon the type of inverter you buy. Some (expensive ones) will pass any external 240V AC through them and only invert if the load is more than the external supply rating. The simplest way would be a break before make source selector switch or a relay can be used to do a similar thing. Do a forum search, we have covered it before.

Thanks, will look into this on previous posts. I suppose the alternative (most simple) option would be an inverter charger, replacing like for like and no new wiring? Though I accept that as you say separates would be more dependable in case one fails

[Woodfern]

47 minutes ago, TheBiscuits said:

 

Try the installation manual not the operator manual ...

 

https://www.manualslib.com/manual/1644904/Trace-Engineering-Sw-Series.html?page=30#manual

Ah - thank you!

[roland elsdon]

Trace inverters were modified sine wave. Noisy as anything, very high power and quality but dated.

we have a small sine wave inverter off the 12v ring which runs small loads tv etc. 240 supply is only off its socket as we have no mains ring

This is seperate to our big inverter in the engine room which runs power tools and again its socket is the only 240 supply.

simple.

[TheBiscuits]

4 minutes ago, roland elsdon said:

Trace inverters were modified sine wave. Noisy as anything, very high power and quality but dated.

we have a small sine wave inverter off the 12v ring which runs small loads tv etc. 240 supply is only off its socket as we have no mains ring

This is seperate to our big inverter in the engine room which runs power tools and again its socket is the only 240 supply.

simple.

 

That's the easy way to get 2m+ separation!

 

I suspect most other boats have a few sockets scattered about the cabin though.

[Woodfern]

1 hour ago, TheBiscuits said:

 

That's the easy way to get 2m+ separation!

 

I suspect most other boats have a few sockets scattered about the cabin though.

 

That would be ideal, but as TheBiscuits says there are 240v sockets throughout so no way of getting separation

[Woodfern]

On 05/08/2021 at 12:26, Tony Brooks said:

 

So it is an amp hour counter and as such the % charged can not be relied upon, but Ah out can be as can volts and amps.

 

There are too many variables for the inbuilt compensation to be correct, so please stop using the % charged read out (read the "Inverter issues" topic). Learn to use tail current at 28.8V  to decide when the batteries are fully charged and rested voltage to assess the state of charge. Once you get the hang of using rested voltage, you can combine the state of charge inferred from that plus the Ah out since fully charged to infer the actual battery capacity that is very unlikely to be what is written on the label. This will help make the % charged a little less inaccurate for a while.

 

 

 

I hope this isn't too much of a derailment of my thread, but on the topic of measuring SOC...

 

Do you know of any threads on here or online articles explaining how to accurately measure SOC based on rested voltage as you suggested? I have found a few charts but have doubts as to their accuracy, and haven't been able to find a discharge curve for my particular batteries. The only detailed online guides I've found only seem to explain it in terms of a battery under a constant load.

 

I've done a calculation based on the Ah drawn since the last 'full charge' (current down to 1% of the stated capacity) and the rested voltage in the early hours of the next morning. I had drawn -27.9Ah according to the smartshunt (actually more, but solar had made up for some). The voltage the next morning after about 3 hours resting was 24.5V. If the generic lead acid battery discharge curve I found is correct, then this makes SOC about 70%, making the actual capacity about 93Ah, rather than the stated 220.

 

The batteries were new a few months ago. It seems I have myself to blame for this having over-discharged them while relying on the shunt's percentage readout and Ah over the voltage. The Solar controller records that on a few days over the last couple of weeks, the voltage under load at the battery has dropped as low as 15-16V overnight. I don't know for how long each time, just that it happened overnight as I woke up to the inverter's low voltage alarm a few times.

 

I think the shunt was also being reset by the solar happening to produce the set 'charged voltage' and 'tail current' on cloudy days or in the shade. It would reset to 0Ah and the next time I checked it would be a healthy -15Ah or something. Not understanding what the voltage under load should look like if that were the case, I would carry on merrily using power and over-discharging the batteries. Then overnight presumably the fridge compressor would turn on and try to draw a large start-up current, the voltage would drop to some horrific level and I would wake up to the inverter's low voltage alarm. I've now set it so it does not automatically reset, and can only be manually reset to 100%/0Ah which I plan to do each day when I run the engine until I see the 1% tail current

 

What do you reckon, another case of lack of proper monitoring = expensive new battery bill?

 

Apologies mods if this should be a separate thread or has already been covered a million times

[Tony Brooks]

22 minutes ago, Woodfern said:

 

I hope this isn't too much of a derailment of my thread, but on the topic of measuring SOC...

 

Do you know of any threads on here or online articles explaining how to accurately measure SOC based on rested voltage as you suggested? I have found a few charts but have doubts as to their accuracy, and haven't been able to find a discharge curve for my particular batteries. The only detailed online guides I've found only seem to explain it in terms of a battery under a constant load.

 

I've done a calculation based on the Ah drawn since the last 'full charge' (current down to 1% of the stated capacity) and the rested voltage in the early hours of the next morning. I had drawn -27.9Ah according to the smartshunt (actually more, but solar had made up for some). The voltage the next morning after about 3 hours resting was 24.5V. If the generic lead acid battery discharge curve I found is correct, then this makes SOC about 70%, making the actual capacity about 93Ah, rather than the stated 220.

 

The batteries were new a few months ago. It seems I have myself to blame for this having over-discharged them while relying on the shunt's percentage readout and Ah over the voltage. The Solar controller records that on a few days over the last couple of weeks, the voltage under load at the battery has dropped as low as 15-16V overnight. I don't know for how long each time, just that it happened overnight as I woke up to the inverter's low voltage alarm a few times.

 

I think the shunt was also being reset by the solar happening to produce the set 'charged voltage' and 'tail current' on cloudy days or in the shade. It would reset to 0Ah and the next time I checked it would be a healthy -15Ah or something. Not understanding what the voltage under load should look like if that were the case, I would carry on merrily using power and over-discharging the batteries. Then overnight presumably the fridge compressor would turn on and try to draw a large start-up current, the voltage would drop to some horrific level and I would wake up to the inverter's low voltage alarm. I've now set it so it does not automatically reset, and can only be manually reset to 100%/0Ah which I plan to do each day when I run the engine until I see the 1% tail current

 

What do you reckon, another case of lack of proper monitoring = expensive new battery bill?

 

Apologies mods if this should be a separate thread or has already been covered a million times

 

Batteries rely on chemical reactions that alter with temperature, battery technology, and battery age, so trying to get accurate figures for discharges is impossible. Voltages under any load is no good unless you specify the load because the higher the load the more volt drop across the battery cells and thus the lower apparent voltage. Rested voltage after the surface charge has dissipated is the only way for the majority of boaters, unless they want to invest in a Smartguage. Typically, the rested voltages to state of charge are as follows, but you will always find sources to contradict this.

 

Before I give the rested voltage values, you need to grasp the fact that the deeper you discharge a battery and the more often you do it the more of its cyclic life you use up. Some "leisure" batteries have a sub 200 cycle cyclic life. Therefore, we try to limit the discharge to no more than 50%. The values I give recognise this.

 

For a 24V system, double the values below.

 

12.7 to 12.8 rested voltage = fully charged

12.5 rested voltage = consider half charged

12.2 to 12.3 = consider it time to recharge ASAP and not use any high loads.

 

In reality, 12.5 = about 3/4 charged and 12.2 to 12.3 = about half charged, but to optimise battery life stick to the above assumptions.

 

I think 10.8 volts is a fully discharged figure, but you would have almost certainly ruined the battery by then

 

You will notice that I have been careful to use words like "about" and "probably". This is because there is so much variation, and only a fool would give definitive values.

 

If you have wet open cell batteries, then you can use a hydrometer or refractometer to assess the state of charge. This has the advantage of allowing a comparison between rested voltage state of charge and hydrometer stat of charge. The further apart these to values the more sulphated, so the less capacity the battery has.

 

If you can live with the present capacity then  do so, although you may need to rethink your electricity use. If you have a charger and shoreline that can do an equalisation charge you may get some recovery in capacity as you may of the solar controller will do it.

 

Consider it a lesson well learned and don't feel too bad about it, hundreds or thousands have slipped up like this before and the same number will do so in the future.

Edited August 11, 2021 by Tony Brooks

[Woodfern]

Cheers @Tony Brooks, makes me feel a bit better!

 

I think the battery charger may also be part of the problem. For something that bulk charges at some 25 amps, it only takes about an hour or so (maybe less) for absorption and then goes into float suspiciously quickly. Could it be that it's going into float too early and not fully charging the batteries?

[Tony Brooks]

Just now, Woodfern said:

Cheers @Tony Brooks, makes me feel a bit better!

 

I think the battery charger may also be part of the problem. For something that bulk charges at some 25 amps, it only takes about an hour or so (maybe less) for absorption and then goes into float suspiciously quickly. Could it be that it's going into float too early and not fully charging the batteries?

 

Most do go into float too early. When it drops into float, turn it off, wait a few minutes, and turn it on again. Repeat until it drops to float almost as soon as you turn it back on.

 

Given enough time, a float voltage of 13.6V should eventually fully charge the batteries, so leaving such a charger on all winter when no one is on the boat is probably OK, but when you are living on the boat discharging every day it may not be. However, as long as the charger is running it, rather than the batteries, will supply the electrical load up to its maximum output.

 

Sometimes I think an old-fashioned stupid charger would do a better job as long as it was monitored and turned off when the charging voltage got within a point or two of the battery's gassing voltage, say 14.5V.

 

 

[Woodfern]

On 11/08/2021 at 12:45, Tony Brooks said:

 

Most do go into float too early. When it drops into float, turn it off, wait a few minutes, and turn it on again. Repeat until it drops to float almost as soon as you turn it back on.

 

Given enough time, a float voltage of 13.6V should eventually fully charge the batteries, so leaving such a charger on all winter when no one is on the boat is probably OK, but when you are living on the boat discharging every day it may not be. However, as long as the charger is running it, rather than the batteries, will supply the electrical load up to its maximum output.

 

Sometimes I think an old-fashioned stupid charger would do a better job as long as it was monitored and turned off when the charging voltage got within a point or two of the battery's gassing voltage, say 14.5V.

 

 

 

I replaced the old Trace inverter/charger which was going into float too early and generating all the buzzing with a new Victron one. I thought that, like my Victron MPPT, I would be able to set the tail current manually and turn off 'adaptive charging'. However, the only options are adaptive (which also seems to go into float ridiculously quickly) or 'fixed' which seems to be fixed time rather than fixed tail current.

 

Could I put it in fixed and then just monitor the current periodically until it's low enough to turn off the engine? Or is there a rule of thumb for how long absorption could be?

 

[Tony Brooks]

16 minutes ago, Woodfern said:

 

I replaced the old Trace inverter/charger which was going into float too early and generating all the buzzing with a new Victron one. I thought that, like my Victron MPPT, I would be able to set the tail current manually and turn off 'adaptive charging'. However, the only options are adaptive (which also seems to go into float ridiculously quickly) or 'fixed' which seems to be fixed time rather than fixed tail current.

 

Could I put it in fixed and then just monitor the current periodically until it's low enough to turn off the engine? Or is there a rule of thumb for how long absorption could be?

 

 

The red bit - First part, yes, as long as the tail current is not taken at the float voltage. It should be in excess of about 14.33 volts.

 

Second part that is the whole problem with adaptive charging, there is no rule of thumb because it depends upon the charger capacity, battery capacity, battery technology, battery age (probably) and temperature. As I understand it, adaptive charging tries to make an informed guess based on the time taken to go into absorption, but you know the result of that guess all too often.