Getting my Tracer MPPT to be a bit more intelligent

[larryjc]

Not sure if this is a silly question or not but I'm sure someone will tell me if it is!!  There was an earlier thread talking about Tracer MPPts and I said that I felt they tend to go into float a little early and that I often up the float voltage manually to 14.5 volts  (normally set to 13.5 - I have Trojans).

At the end of a days motoring my batteries are normally topped right up (they're often full in the morning with 500w of panels and good sunshine).  So the Tracer quite sensibly goes straight to float.  But if I turn my inverter on or the Tele and draw 5-6 amps (recharging laptop takes a lot) then the Tracer seems to ignore the need to supply more amps and I go into discharge.  However, if I bang the float up to 14.5 I will be positively charging again.   Surely if the tracer sees a net discharge it should put in more amps irrespective of the volts its set at?  I have the number of key strokes to change the float value down to a fine art and its not really a problem - just wondering.

[nicknorman]

3 hours ago, larryjc said:

Not sure if this is a silly question or not but I'm sure someone will tell me if it is!!  There was an earlier thread talking about Tracer MPPts and I said that I felt they tend to go into float a little early and that I often up the float voltage manually to 14.5 volts  (normally set to 13.5 - I have Trojans).

At the end of a days motoring my batteries are normally topped right up (they're often full in the morning with 500w of panels and good sunshine).  So the Tracer quite sensibly goes straight to float.  But if I turn my inverter on or the Tele and draw 5-6 amps (recharging laptop takes a lot) then the Tracer seems to ignore the need to supply more amps and I go into discharge.  However, if I bang the float up to 14.5 I will be positively charging again.   Surely if the tracer sees a net discharge it should put in more amps irrespective of the volts its set at?  I have the number of key strokes to change the float value down to a fine art and its not really a problem - just wondering.

Bear in mind the difference between amps and volts. If the batteries are full and the Tracer is in float at 13.6v and you then demand 5-6A for the inverter, the voltage should stay at 13.6v but the Tracer should now be outputting 5-6A. When you say “I go into discharge” do you mean the battery voltage falls significantly below 13.6v?

[Dr Bob]

I guess Larry means the system shows 5A out but the voltage is still over 13V so the mppt hasn't kicked in yet. This happens all the time with my victron mppt. Put a bit more draw on and the mppt starts delivering. Surely it's just the voltage has not yet reduced to the point where the tracer is out of float.

[larryjc]

12 hours ago, nicknorman said:

Bear in mind the difference between amps and volts. If the batteries are full and the Tracer is in float at 13.6v and you then demand 5-6A for the inverter, the voltage should stay at 13.6v but the Tracer should now be outputting 5-6A. When you say “I go into discharge” do you mean the battery voltage falls significantly below 13.6v?

No the voltage stays the same but the extra 5-6 does not appear and my BM2 shows a discharge as it does not output the extra amps that the panels could give.  I have to manually up the voltage to 14.5 to get a positive current output again.

[WotEver]

1 hour ago, larryjc said:

No the voltage stays the same but the extra 5-6 does not appear and my BM2 shows a discharge as it does not output the extra amps that the panels could give.  I have to manually up the voltage to 14.5 to get a positive current output again.

You don’t say how big your bank is but if it’s say 550Ah then you’d have to have that drain on for an hour to use 1% of capacity. In other words it’s a negligible draw which doesn’t depress the voltage and hence the Tracer doesn’t acknowledge that the batteries need a tiny bit of a charge. 

[nicknorman]

1 hour ago, larryjc said:

No the voltage stays the same but the extra 5-6 does not appear and my BM2 shows a discharge as it does not output the extra amps that the panels could give.  I have to manually up the voltage to 14.5 to get a positive current output again.

That suggests to me the Solar is wired incorrectly - on the battery side of the shunt. If the voltage remains up at 13.6v then it’s not feasible for the batteries to be outputting 5-6 A. So either a mis-wire or possibly a high resistance connection somewhere giving misleading voltage readings. You should check the voltage actually on the battery terminals during this “discharge” using a multimeter. If they remain at 13.6v, the current isn’t coming from the batteries.

[larryjc]

Hmm - I think that Wotever might be right.  Pretty sure my wiring is OK as I redid it all recently.  If the panels are holding the volts up at 13.6 I don't see why you still can't draw current from the batteries  and anyway by putting the volts up to 14.6 makes the tracer use the current that the panels are clearly capable of producing.  As I said its not really an issue I was more curious than anything else.

[nicknorman]

3 hours ago, larryjc said:

If the panels are holding the volts up at 13.6 I don't see why you still can't draw current from the batteries

Because 13.6v is above the natural reaction potential of the cells. The basic physics / chemistry means that a 12v battery can’t deliver a  current into a load whilst the terminal voltage is being held up at 13.6v.

[Tony Brooks]

And if the solar panels can still supply the new current demand without lowering the charge voltage its the panels that supply the load. If the laod was high enough (Amps) it would pull the panel voltage down so the batteries would supply some current.

[larryjc]

Yeah - I've been ruminating on that and realised that point about volts and discharge..  The NASA is correctly wired as I did it but maybe I should look at its zero current setting.  I have noticed that can wander off over time.  As I use about 50AH per 24 hours on 440 AH of batteries I'm not too fussed.  Maybe a delve into the wiring might be worthwhile idc.  However I still say the Tracer goes into float too early.

[Richard10002]

1 hour ago, larryjc said:

Yeah - I've been ruminating on that and realised that point about volts and discharge..  The NASA is correctly wired as I did it but maybe I should look at its zero current setting.  I have noticed that can wander off over time.  As I use about 50AH per 24 hours on 440 AH of batteries I'm not too fussed.  Maybe a delve into the wiring might be worthwhile idc.  However I still say the Tracer goes into float too early.

I have a Tracer BN MPPT controller and dont really understand how it decides what to do, and when.

 

However, I have it set at the maximum period for Absorption, which is 180 minutes. I'd guess it depends on the power of the sun as to whether 3 hours is long enough at Absorption voltage.

 

In fact, I don't actually sense any logic regarding how it decides to start the Absorption period.... it would seem crazy for it to start as soon as the sun provides a bit of power, (a bit after dawn??), or even when the sun exceeds a certain amount of power, as the 3 hours could then be during the weakest period of sun, given that the power will vary with cloud cover and density.

[larryjc]

Yeah I noted that although in instructions it uses the term 'boost' rather than absorption although I guess they mean the same thing.  I might have a word with Bimble - if I get an answer I'll put it here.

On another note having had some previous advice here I thought I'd recheck the wiring.  When I got to the earth lead from the batteries to the shunt - the one I paid a professional chandlery to make up for me - I discovered that the crimped fitting on the shunt end had almost pulled out.  Having re-crimped it properly my volts and amps are all starting to make sense again.  If in doubt - do it yourself!!!

 

Edit - just checked my emails as I had a dialogue with Bimble last year.  The problem then was that the controller was holding the volts at boost even though the batteries were well full (after 6 hours motoring) - so I reduced the boost time to 10 minutes which is probably why they seem to go to float too early now.  It would seem that rather than an intelligent algorithm for swapping from boost to float it simply uses a time delay.  I shall fiddle with this to get a compromise.  Mind you of I was not on shore power and not using the engine it seems to me that 180 minutes is far too little.

Edited June 20, 2018 by larryjc

[Detling]

I believe the boost time is just that a timer, so when the controller decides the batteries are out of bulk charge and into adsorption or boost (by a simple voltage measurement) then the tracer runs at boost voltage for the time set, it doesn't look at amps. If cloudy you get a few amps at boost voltage fpr the duration of the timer, if sunny you may get 10 times that, at the end of the time it goes into float and just trickle charges until the reconnect voltage is reached, which is way down about 12.4V I think. If you turn a decent load via an inverter say 50+ amps then the battery voltage will drop, and the Tracer kick back in to charge mode.  Remember the Tracer has no way of knowing the amps your batteries are supplying elsewhere, it can only see the voltage which is slow to react.

[Richard10002]

8 hours ago, Detling said:

at the end of the time it goes into float and just trickle charges until the reconnect voltage is reached, which is way down about 12.4V I think.

I think you can vary the reconnect voltage.... would it be OK to increase it, and what to?

[WotEver]

7 hours ago, Richard10002 said:

I think you can vary the reconnect voltage.... would it be OK to increase it, and what to?

12.55?

[Detling]

you can increase reconnect to just below the float voltage. I have my boost and equalisation voltage at 14.4 my float at 14.3 and my reconnect at 14 but I have sealed AGM which don't like over 14.4 and they recommend 13.8 as a float. The Batteries limit the current when they are over 80% charged and over 95% they throttle my solar to 5 or 6 amps maximum. With a daily use of 120Ah my 600 watts usually takes untill 13:00 to get the batteries full, in full sun so I over charge slightly in the afternoon on a sunny day. On a dull day they only just about make it by tea time. With a timed adsorption sods law says the clouds come and you get 2 hours of 4 amps then and drop into float, so the high float basically keeps it charging. I do have a switch to disconnect 400 watts of panel for when we leave the boat shut down whilst we go home or on holiday, there is also a timer so the solar is only connected for two days in a week, that way I hope I am not overcooking the batteries.

[larryjc]

52 minutes ago, Detling said:

you can increase reconnect to just below the float voltage. I have my boost and equalisation voltage at 14.4 my float at 14.3 and my reconnect at 14 but I have sealed AGM which don't like over 14.4 and they recommend 13.8 as a float. The Batteries limit the current when they are over 80% charged and over 95% they throttle my solar to 5 or 6 amps maximum. With a daily use of 120Ah my 600 watts usually takes untill 13:00 to get the batteries full, in full sun so I over charge slightly in the afternoon on a sunny day. On a dull day they only just about make it by tea time. With a timed adsorption sods law says the clouds come and you get 2 hours of 4 amps then and drop into float, so the high float basically keeps it charging. I do have a switch to disconnect 400 watts of panel for when we leave the boat shut down whilst we go home or on holiday, there is also a timer so the solar is only connected for two days in a week, that way I hope I am not overcooking the batteries.

I have Trojans and left the boat with all 500w all winter with a float of 13.5 - they were fine when I got back.  I might look at upping the reconnect figure as a way of not having to regularly and manually up the float amount to get the last bit out of them.

[Detling]

4 hours ago, larryjc said:

I have Trojans and left the boat with all 500w all winter with a float of 13.5 - they were fine when I got back.  I might look at upping the reconnect figure as a way of not having to regularly and manually up the float amount to get the last bit out of them.

As I understand it positive grid corrosion takes time to kill a battery, a bit like rust takes time to sink the boat. The big gamble is will the batteries die a natural death before positive corrosion gets them or not. According to one motorhome web site more batteries are now dying from overcharging than from sulphation and the suspect is having solar running 365 days a year the battery used for say 40 days a year.

[larryjc]

You can't win!!  Mind you when I was sailing, my boat had 4 Trojans with solar.  I had them for two years and I know they were still going strong 8 years on.  My experience of motorhomes is that they use too few and rubbish batteries as they most always plug in every night.  I can't see that there is much difference between keeping a charger on all the time or solar as long as the float volts are correct for the type of battery.