Sterling Pro Charge Ultra 60A Cable size?

[Richard10002]

Bought the Sterling Pro Charge Ultra 60A charger in Midland Chandlers Freaky Friday to replace a 25A charger. The existing cables are 7mm outside diameter, which suggests 8.5mm2 which it seems can carry 60A, or so.

The Sterling manual states 50mm2 cable for my 4m round trip to the batteries and back.

Presumably, the Sterling specification is related to voltage drop, rather than cable carrying capacity, but I am no expert.

If I connect the existing cable to the charger, and run it at full power, will the 60A, (for a while), burn out or overheat the 8.5mm2 cable, or will the batteries merely see a lower voltage, and perhaps not the full 60A? I suppose I am asking if 8.5mm2 cable can carry 60A safely.

For information, the charger can be set to deliver 75%, 50%, or 25% of it's max power, so I can set it to deliver 45A, 30A, or 15A, if necessary in the short term.

I'll obviously get some thicker cable in due course, but it would be good to connect things up and try it out sooner, rather than later.

[MtB]

1 hour ago, Richard10002 said:

Presumably, the Sterling specification is related to voltage drop, rather than cable carrying capacity, but I am no expert.

 

Correct in my opinion. But I am no expert either.

1 hour ago, Richard10002 said:

If I connect the existing cable to the charger, and run it at full power, will the 60A, (for a while), burn out or overheat the 8.5mm2 cable,

 

No.

 

1 hour ago, Richard10002 said:

or will the batteries merely see a lower voltage

 

Yes.

 

1 hour ago, Richard10002 said:

and perhaps not the full 60A?

 

Yes.  But once bulk charging has finished they won't anyway.

 

1 hour ago, Richard10002 said:

I suppose I am asking if 8.5mm2 cable can carry 60A safely.

 

Probably, BIANAE.

 

1 hour ago, Richard10002 said:

For information, the charger can be set to deliver 75%, 50%, or 25% of it's max power, so I can set it to deliver 45A, 30A, or 15A, if necessary in the short term.

 

Not necessary in my view. I addition you have to manually set % every time you power it up IIRC. A right PITA.

Edited March 16, 2018 by Mike the Boilerman
Speeling error

[Boater Sam]

4 metre total @ 60 amps I would use 16mm sq cable at least. Its not worth short cutting, the charger will see the volts drop on thin cables and shut down early, in which case you have wasted money buying a good charger.

That 8.2 mm sq is not a size, are you saying the cable is 7mm OD over the insulation?  If so it sounds like its only 6 mm sq at best!  Too thin.

[Tony Brooks]

Depends how old the cables are. Modern thin wall 8.5 sq mm CCSA cable has an OD of 5.6 mm and is rated at 63 amps so thin wall 7mm OD is likely to be maybe 10 amps higher. (Vehicle Wiring Products data).

Older non-thin wall cable will have a lower CCSA for the same OD but I don’t have the data to hand. Extrapolating from the data I have it seems 7mm OD non-twin wall cable would be about 50 amp cable so too thin and it may well get warm at maximum power. I would not use it.

So the first thing to find out is it standard PVC or thin wall PVC.

 

I disagree with Sam about the charger shutting down early although it may go into float early but that is a "feature" it seem of adaptive charging. I think Mike's replay has it about right. Remember once the batteries rather than the charger starts limiting the charging current it will start dropping and the more iyt drops the lower any voltdrop on the cable will be so the charging voltage at the batteries gradually becomes closer to that at the charger.  I do agree that its npot woprth skimping on cable size. Too large can hurt nothing but your pocket, too small can and will cause problems.

Edited March 16, 2018 by Tony Brooks

[Sea Dog]

Bear in mind that if your batteries are pretty much full and you're not running anything heavy, the charger won't be delivering anything like max amps, probably just low single figures.  In normal use, with just lighting and the fridge as 12V load, mine doesn't drop out of float.  Of course, it could and there may be a time it will, and if for some reason you need to charge heavily depleted batteries you'll see a much higher current, so I'd fit the right cables asap.

[Richard10002]

My plan, (i.e. within a couple of weeks), is to buy and fit 50mm2 cable. In the meantime I just wanted to connect things up to get it working and see how the features work, compared to how I thought they would work.

I'm going to set float voltage the same as absorbtion voltage, (14.9V for severely depleted Trojan T105s), so going into early float shouldnt be an issue.

I just want to sure that I'm not going to start a fire in the cable at 60A. In the event, I'll probably set it to run at 30A in order to minimise any risk.

Thanks for the input - all very helpful 

[smileypete]

17 hours ago, Richard10002 said:

Bought the Sterling Pro Charge Ultra 60A charger in Midland Chandlers Freaky Friday to replace a 25A charger. The existing cables are 7mm outside diameter, which suggests 8.5mm2 which it seems can carry 60A, or so.

The Sterling manual states 50mm2 cable for my 4m round trip to the batteries and back.

Presumably, the Sterling specification is related to voltage drop, rather than cable carrying capacity, but I am no expert.

If I connect the existing cable to the charger, and run it at full power, will the 60A, (for a while), burn out or overheat the 8.5mm2 cable, or will the batteries merely see a lower voltage, and perhaps not the full 60A? I suppose I am asking if 8.5mm2 cable can carry 60A safely.

For information, the charger can be set to deliver 75%, 50%, or 25% of it's max power, so I can set it to deliver 45A, 30A, or 15A, if necessary in the short term.

I'll obviously get some thicker cable in due course, but it would be good to connect things up and try it out sooner, rather than later.

It does look like you've probably misread the manual there, it looks like they quote cable sizes for distance separation between charger and batts, in which case you want 25mm2.

Usual rule of thumb is 'amps divided by three' so 60/3 = 20, rounded up to the next size of 25mm2. This would be good for 5m separation between batts and loads on 12V, and half that distance for charge sources.

Easy way to work out volt drops is that 'amps divided by three' gives a volt drop of 50mV per metre of cable, as 1mm2 copper has a resistance of 0.017 ohms.

Edited March 16, 2018 by smileypete

[Sea Dog]

6 hours ago, Richard10002 said:

I'm going to set float voltage the same as absorbtion voltage, (14.9V for severely depleted Trojan T105s), so going into early float shouldnt be an issue.

Check those figures Richard because I think that staying in float at 14.9v will have your batteries gassing for extended periods and do them no good at all.  13.8v would be more typical, but Victron have started to add a further "storage" mode of 13.2v to their chargers for normal lead acid batteries to minimise corrosion at the positive plates. They hold them at this for a week at a time before chopping back into absorption for a period.

[nicknorman]

8 minutes ago, Sea Dog said:

Check those figures Richard because I think that staying in float at 14.9v will have your batteries gassing for extended periods and do them no good at all.  13.8v would be more typical, but Victron have started to add a further "storage" mode of 13.2v to their chargers for normal lead acid batteries to minimise corrosion at the positive plates. They hold them at this for a week at a time before chopping back into absorption for a period.

Is he running it from a genny or from the mains? Can’t remember, but if from a genny it won’t be an issue.

[Richard10002]

Thanks Nick.. Genny it is, completely off grid. Not only is it not an issue, it is exactly the reason I want the Sterling facility to custom set float and absorption at the same level.

[nicknorman]

2 minutes ago, Richard10002 said:

Thanks Nick.. Genny it is, completely off grid. Not only is it not an issue, it is exactly the reason I want the Sterling facility to custom set float and absorption at the same level.

Yes I thought so, in which case you are doing the right thing.

[Richard10002]

What I've done:

My Sterling 2500W inverter charger is connected to the batteries with 95mm2 cable. So I bought some 25mm2 cable and connected the terminals of the charger to the terminals of the inverter charger via an 80A Mega Fuse, so I have about a metre of 25mm2 cable, then 95mm2 cable from charger to batteries.

I suppose my only concern is, if the inverter is drawing 200A from the batteries to run a 2500w AC appliance, could 200A find its way to the new charger. Instinct tells me that these things sort themselves out as, ultimately, everything on the DC side of a boat is connected to everything, given that all routes end at the battery +ve terminal, and the shunt terminal.

[Boater Sam]

You then have 2 chargers connected to the batteries, yes?

If one is off, the other will block the DC from the other no problem.

If both are on, the one with the lowest final voltage setting will shut itself down first.

I see no problem there but do you really need to charge the batteries so fast, its not good for them?

Of cousre you should not run the mains charger when you are using the inverter to provide 240v power, perpetual motion does not work!

[Richard10002]

33 minutes ago, Boater Sam said:

You then have 2 chargers connected to the batteries, yes?

If one is off, the other will block the DC from the other no problem.

If both are on, the one with the lowest final voltage setting will shut itself down first.

I see no problem there but do you really need to charge the batteries so fast, its not good for them?

Of cousre you should not run the mains charger when you are using the inverter to provide 240v power, perpetual motion does not work!

Thanks for that - reassuring

1) I dont need to charge the batteries any faster than the 60A starting current of the new charger. However, if I want 240V through the boat, I need to turn the inverter charger on, so both can be on at the same time.

2) The shore power goes into a consumer unit which has 2 RCDs... 1 goes to the inverter charger, and the other to a 240V socket which I only use for the new charger, but which could obviously be used for other 240V appliances.

3) the inverter 240V output goes to a second consumer unit which supplies the boats 240v ring, (or whatever you call it).

2) & 3) mean that there is no way of 2 x 240v AC supplies being connected to an AC input at the same time, (Hope that makes sense, and that I am correct). At my last BSS the inspector looked quite closely at my arrangement and was happy with it.

 

 

[Neil Smith]

Why do you need another charger? I thought the charger side of your inverter charges at 60 or 70 amps, I know mine does.

Neil

[Richard10002]

1 hour ago, Neil Smith said:

Why do you need another charger? I thought the charger side of your inverter charges at 60 or 70 amps, I know mine does.

Neil

Where to start  It could be a function of my situation, rather than the inverter charger, but I wont be alone:

1) If the 240V source supplying the inverter charger in charging mode fails, (shore power trips, genny runs out of petrol, etc... ), the inverter charger reverts to inverter mode, and depletes the batteries at a rate of 4A even if nothing is connected to the 240V outputs. This didnt really matter much to me as i am mostly off grid and use a genny rather than shore power. A year or so after I bought mine, (2012), Sterling modified the model to allow a user to turn the inverter mode off, but they wouldnt help with an upgrade to mine.

2) a) The charging algorithm means that, once bulk charging has finished, absorption time is "smartly" set at 10 times the time of bulk charging, or 60 minutes, whichever is the higher, up to a max of 4 hours, (I think). Bulk charging very rarely exceeded 6 minutes, so absorption time was rarely more than the 1 hour minimum, after which it reverted to float voltage of 13.5V or so.

2)  1 hour, (or whatever the smart algorithm decided), was never close to being long enough to charge the batteries to the point where the tail current was low enough to consider them full... as we all know, this can actually take many hours. In order to work around this, the charger needed to be turned on and off several times during the daily charging process, which meant setting an alarm at about 55mins. If I didnt set an alarm, I would often forget to reset the charger, and find that it had been float for several hours of the genny running - I can't tell you how annoying and irritating this was, albeit a bit of a 1st world problem.

The pro Charge Ultra has a custom setting where you can set absorption and float voltages at whatever you want up to 15.1V. I set both to 14.7V such that it is "set and forget" and, whatever the algorithm decides is a "smart" time to revert to float voltage, it remains at the voltage I want for as long as it is running.... which is when I turn it off, or when the genny runs out of fuel - in the latter case, there is no inverter to revert to, so my batteries dont get depleted..

 

I would guess that you have access to shore power, in which case being in float mode wont matter so much as it will eventually charge to full. I would also guess that you may have a later model where you can turn the inverter function off when charging.

Heres a thread which talks more about my issues and reasoning - the Pro Charge Ultra discussion starts around post #118 where I ask Mtb a bit about it.

 

[Neil Smith]

Yes I have shore power on my leisure  mooring but rarely use it, I have solar that keeps the batteries at 100% when we are not there, I also have an old pro combi of 2010 vintage but not fitted until 2015 and we had a problem last winter when we used a dehumidifier to stop damp, the shore line tripped and when we went back 4 days later the traction batts were flat as the inverted was running the dehumidifier, so in your case I can understand why now.

Neil