Float Charge current

[Winter 42]

Have recently added a new 3stage TBB charger(40A) from AA solar.

 

It charges nicely. When it goes to float stage (13.4 +/- a tad for temperature sensor) It still shows a pretty constant 1.4ish amps going in.

 

I had thought the current during float stage would be way down, less than half an amp.. but I dont know. Does approx 1.4A float current sound right?

 

Bank is Flooded, 2x 230ah in parralel. Batterys approx 4 years old. Levels are good, plates are all covered.

[Winter 42]

That 1.4a would probably include the always on loads - one BEP DC monitor and the always on feed to the stereo to remember the stations. Cant see either of those two drawing more than about 0.1A

[mattm 98]

Is the 1.4a figure from the bep meter or the chargers display?

 

If from the charger, what does the bep say?

[Winter 42]

1.4a figure read off the charger display.  

The Charger is currently connected directly to the battery (not via the shunt(I need to add a busbar first)) so the BEP reading is not much use. 

The BEP reads 0, which would indicate that the 1.4a is not being supplied to a load but rather going into the battery itself. 

[wheels 543]

Needing one critical piece of info. How old is the battery bank?
Ooops, I see you stated that above.

First thing you need to do is get a digital meter and verify the Voltage.

It could also be that the Battery was not at 100% charge. As the charge state increases, the battery resistance increases and this is actually what causes multi stage chargers to switch to the various stages.

Is the regulator using a remote temp sensor fitted to the battery, or using an internal sensor. If internal, is the Reg in an area that gets the same ambient temperature as the Bank. As temperature rises, the charging voltage should drop. It sounds like it is doing that, but if the reg is not as warm as the Bank, then it may not be dropping enough. You can check that by measuring the temp at the bank. Then you need to do a little math. For every degC above 25dgC, you subtract 3.9mV per cell. So 6 cells for a 12V Battery. If the Boat is heating the bank up to say 30dgC, then the float voltage only wants to be 13.28V. It does not sound a lot, but it makes a big difference and that is why you need to make sure the voltages are actually correct with a digital meter.

You don't need a Bus bar, connect the Solar Reg Neg output directly to the shunt terminal if you can. That's the terminal that feeds the Boat, not the terminal on the battery side of the Shunt. Connecting directly at the shunt on the same terminal as the feed, allows the best possible reading accuracy via the Reg.
The positive supply from the reg can go directly to the battery, although I prefer connections on the battery side of the Isolator switch. Terminals on the battery are more prone to corrosion. It is good practice to fit a Fuse or Circuit breaker at this connection point. Remember that the wire is connected directly to a very impressive energy source that would simply melt the wire if a short ever developed anywhere between it and the Reg.
Oh and make sure you have a decent current capacity cable running from the Reg to the battery. 40A is a sizable amount of current. So OK, you won't get the full 40A, but lets say you have 20A or more. There can be a sizable voltage drop in the cable if it is too light a gauge and as you see with the voltage changes being so small, it can dramatically upset charging accuracy.

 

[Winter 42]

What was the tail current when the  charger was still on absorbtion voltage?

I suspect at 1.4A, no load, bats not 100%.

Also need to check accuracy of that current with a clamp meter.

 

Yes, I could check that current reading, but I suspect it is correct.  At full bulk charge it reads nearly bang on the rated current (39.7A) so I believe the current readout is correct on the charger. 

Tail current - I've not watched for this - I'll have to sit and watch it next time. 

First thing you need to do is get a digital meter and verify the Voltage.

 

Sure - but the voltmeter on the charger display and the voltmeter in the BEP match - so I trust the voltage reading.   

 

It could also be that the Battery was not at 100% charge. As the charge state increases, the battery resistance increases and this is actually what causes multi stage chargers to switch to the various stages.

 

Is the regulator using a remote temp sensor fitted to the battery, or using an internal sensor. If internal, is the Reg in an area that gets the same ambient temperature as the Bank. As temperature rises, the charging voltage should drop. It sounds like it is doing that, but if the reg is not as warm as the Bank, then it may not be dropping enough. You can check that by measuring the temp at the bank. Then you need to do a little math. For every degC above 25dgC, you subtract 3.9mV per cell. So 6 cells for a 12V Battery. If the Boat is heating the bank up to say 30dgC, then the float voltage only wants to be 13.28V. It does not sound a lot, but it makes a big difference and that is why you need to make sure the voltages are actually correct with a digital meter.

 The Temp sensor is affixed with 3m sticky tape to the battery.  The charger gives a readout in degrees C of the battery temp - which goes up and down with the heat of the day - so the temp sensor is working

 

Laterals 0.5A float seems closer to what I would expect. Would plate sulfation cause excess float current?

 

You don't need a Bus bar, connect the Solar Reg Neg output directly to the shunt terminal if you can. That's the terminal that feeds the Boat, not the terminal on the battery side of the Shunt. Connecting directly at the shunt on the same terminal as the feed, allows the best possible reading accuracy via the Reg.

The positive supply from the reg can go directly to the battery, although I prefer connections on the battery side of the Isolator switch. Terminals on the battery are more prone to corrosion. It is good practice to fit a Fuse or Circuit breaker at this connection point. Remember that the wire is connected directly to a very impressive energy source that would simply melt the wire if a short ever developed anywhere between it and the Reg.

Oh and make sure you have a decent current capacity cable running from the Reg to the battery. 40A is a sizable amount of current. So OK, you won't get the full 40A, but lets say you have 20A or more. There can be a sizable voltage drop in the cable if it is too light a gauge and as you see with the voltage changes being so small, it can dramatically upset charging accuracy.

This is just because I already have too much connected to the load side of the shunt - heavy gauge cable for the windlass, the macerator, etc, there will be no thread left on the bolt on the shunt if I add another ring terminal!

 

My charger is connected with only 1m of heavy wire (can't recall the size, but the cables were supplied by a marine sparky who asked what voltage, current, and length, - he chose the cable size).

 

I haven't yet fused the charger - its on my list. (Need to work out what form of fuse holder/breaker will mount nicely in the space provided. )

 

I should add this charge current seems to be consistently like this - Ie its not just started doing it. I've had the charger for a month and it seems whenever I come to the boat it is on float and sitting above 1A charging.

[wheels 543]

 

Laterals 0.5A float seems closer to what I would expect. Would plate sulfation cause excess float current?

Yes the 0.5A is probably closer to the ideal. But also yes, sulphation can cause issues.

It depends on their history. If they have had an oopsy or two in their history, or just plain abuse, that can lead to a problem. Plate degrading means the battery never accepts full charge anymore and the self discharge can increase. If this happens, then any reg/charger connected will start to continuously charge rather than ever going into a full float. That could result in exactly what you are seeing with the 1.4A current. It is something you cannot ever reverse. If your charger can carry out an equalisation charge, I recommend you do so. This actually is good practice to do once a month.