Solar Panels and Smartgauge

[Theo]

My Smartgauge/Smartbank Advanced has worked faultlessly for the last 13 years.  When I fitted my solar panels I asked Gibbo (the designer of SG) if I should annect the output of the controller to the engine battery/alternator's side of the relay.  He said no, connect it to the domestic side.  This I did and all worked well while we were living aboard.

 

When we stopped living aboard I relied on the solar panels to keep the batteries topped up and this they have done very successfull.  I always return to Theodora to find the batteries at 100%.  Except that the percentage refers to the domestic bank.  The engine battery has not been charged and I have to use the emergency connect to sart the engine.

 

Questions: What is the reason for Gibbo's advice?  If I connect the solar panels to the alternators/engine battery side will it not keep the engine battery topped up and then energise the relay to keep the domestics topped up?

 

Any thoughts?

 

Nick

 

 

Edited July 13, 2021 by Theo
fat fingers

[frangar]

Fit a blue sea VSR and they will sense either bank. This means keep the wiring as it is so it’s the domestics getting charged “first”…so if the fridge etc pulls the voltage down a bit the panels will put any charge into the domestics…and when the voltage rises they will keep the engine battery happy. 

[David Mack]

Link the domestic and engine batteries with a dual sensed Voltage Sensitive Relay (VSR). Then whichever battery your solar, alternator, mains charger etc is connected to, both batteries will be charged by the various charging sources. 

I have the alternator connected to the start battery (yes I know, but the boat came that way), and solar to the domestic. Fully charged batteries whenever I arrive at the boat, even in the depths of winter.

[dmr]

I'm not really sure how Smartbank works, but I think its just an extra clever VSR.

There might be a subtle Smartbank reason for connecting Solar to domestic, but my guess is that its not that important and just a bit nicer to do it one way rather than the other.

Do you have a big solar array?

The domestic batteries can get quite low and take some big charge currents whilst the starter battery is mostly fully charged, so a direct connection to the domestic bank puts less current through the relay contacts????

 

.................Dave

[Theo]

35 minutes ago, dmr said:

I'm not really sure how Smartbank works, but I think its just an extra clever VSR.

There might be a subtle Smartbank reason for connecting Solar to domestic, but my guess is that its not that important and just a bit nicer to do it one way rather than the other.

Do you have a big solar array?

The domestic batteries can get quite low and take some big charge currents whilst the starter battery is mostly fully charged, so a direct connection to the domestic bank puts less current through the relay contacts????

 

.................Dave

I rather think that the answer may be in the set of instructions that Gibbo wrote:

 

Do not be alarmed and assume a fault if the battery paralleling relay is alternating between
connected and disconnected. This is not a fault in SmartGauge or SmartBank. It could be that the
system is doing exactly what it is supposed to do. i.e. preventing cross discharging between
battery banks. But it is possible that it is the result of either incorrect settings (connect and
disconnect voltages set too close) or far more likely, a charger that is simply far too small for the
total batteries in the system. Even with a charger that is too small, it is usually possible to find a
compromise in the settings that allows the system to operate until the charger is replaced with
one of the correct size.

 

It may be that Gibbo advised the connection to the domestics to avoid this.  The solar panels will often look like a very inadequate charger.

 

Nick

Edited July 13, 2021 by Theo

[Iain_S]

Connection of charging sources to the domestic bank rather than the start battery minimises the strain on the connecting relay, although with the recommended relay with Smartbank, this shouldn't be a problem.

 

The Smartbank functions as an adjustable, (very) heavy duty, VSR, and the setup should work to keep both battery banks charged.

 

On Kelpie, even after several months absence, the starter battery will start the engine, even without having had a charge source. On Gamebird, I often have to use the EC function to start the engine, but that's down to a starter battery that should be drawing a pension!

 

Might be worth checking voltages, connection status, etc when on the boat and the sun is shining. The 100% reading on the domestic bank may be unreliable during the daytime : if the solar was only getting to 13V or so, it might not be charging, but Smartgauge would interpret this as battery voltage and get to 100% charged. Smartgauge seems to learn to cope with alternator charging and be reasonably accurate while charging, but it can't cope with the varying voltage from solar.

 

 

 

 

[Theo]

2 hours ago, Iain_S said:

Connection of charging sources to the domestic bank rather than the start battery minimises the strain on the connecting relay, although with the recommended relay with Smartbank, this shouldn't be a problem.

 

The Smartbank functions as an adjustable, (very) heavy duty, VSR, and the setup should work to keep both battery banks charged.

 

On Kelpie, even after several months absence, the starter battery will start the engine, even without having had a charge source. On Gamebird, I often have to use the EC function to start the engine, but that's down to a starter battery that should be drawing a pension!

 

Might be worth checking voltages, connection status, etc when on the boat and the sun is shining. The 100% reading on the domestic bank may be unreliable during the daytime : if the solar was only getting to 13V or so, it might not be charging, but Smartgauge would interpret this as battery voltage and get to 100% charged. Smartgauge seems to learn to cope with alternator charging and be reasonably accurate while charging, but it can't cope with the varying voltage from solar.

 

 

 

 

Thanks Iain.  That makes good sense.  I am using the recommended relay.  It was all supplied by Gibbo. (I wonder where he is now.  I do miss his contributions)

 

Nick

[Theo]

Having fitted the new Victron controlle as advised elsewhere and discovered that it is vey good and done an experiment or two I now have some answees and another question.

 

I tried fitting connecting the output from the MPPT to the alternator/engine battery side of the relay.  This should have meant that the Smartbank advanced woould have treated the solar panels as a normal charge source and charged the engine battery in preference to the domestics until it was fully charged.  At that point it should have energised the relay and included the domestics.  Smartbank certainly tried to do that but at times the charging current was so low that it did not energise until Smartbank Advanced's "Hold" function was activated.  It would hold for a few minutes and then deenergise the relay for another few minutes then go on to hold again.  The result was that the intelligent charging feature of the MPPT got really confused by the repeated changing of the battery bank size from 90Ah to 600Ah.  The MPPT would go on to different charging regimes (absorption, bulk, float) when what it really needed was to stick with bulk.

 

I have now changed back to Gibbo's recommendation to connect it directly to the domestics and all is well except...

 

... for the fact the the solar panels no longer charge the engine battery.  This is a nuisance.

 

Dow anyone have any thoughts?

 

Nick

[Alan de Enfield]

1 minute ago, Theo said:

Dow anyone have any thoughts?

 

 

Put a 'jump-lead' from your domestics to your starter battery.

 

Is is very rare for a starter battery to go-flat as starting the engine takes only a very few amps and is replaced 'within minutes' of engine running, you may suffer some self-discharge if you are not using the starter for weeks on end, but, it will be a minimum amount (maybe 1% per week).

 

A starter battery should not really require any suplementary charging.

[Tony Brooks]

On the KISS principle, I think I would ditch the Smartbank relay and fit a VSR as recommended above.

[MtB]

7 minutes ago, Tony Brooks said:

On the KISS principle, I think I would ditch the Smartbank relay and fit a VSR as recommended above.

 

I agree. My starter batteries seem quite happy to be left for months at a time occasionally, and always work fine when called upon.

 

I'm wondering if there is a small but unnoticed constant drain on Theo's start battery, causing it to go flat.

[Tony Brooks]

Actually on JennyB I started to suffer occasional flat start battery symptoms but I could never pin it down. I suspected a bad connection somewhere, but I could not find it. This went on for a year or so. Until I found the start battery absolutely flat. Then it dawned. Starting needs very few Ah so if I got to the boat around noon or later the solar and VSR had put enough charge into the battery to start the engine. If I got there in the morning or on a dull day, the solar had not charged it enough to start. When aboard, the alternator kept on top of the start battery self discharge. It had a shorting cell that gradually got worse. Possibly the only drawback to solar I have found.

[Bobbybass]

On 13/07/2021 at 17:16, Theo said:

My Smartgauge/Smartbank Advanced has worked faultlessly for the last 13 years.  When I fitted my solar panels I asked Gibbo (the designer of SG) if I should annect the output of the controller to the engine battery/alternator's side of the relay.  He said no, connect it to the domestic side.  This I did and all worked well while we were living aboard.

 

When we stopped living aboard I relied on the solar panels to keep the batteries topped up and this they have done very successfull.  I always return to Theodora to find the batteries at 100%.  Except that the percentage refers to the domestic bank.  The engine battery has not been charged and I have to use the emergency connect to sart the engine.

 

Questions: What is the reason for Gibbo's advice?  If I connect the solar panels to the alternators/engine battery side will it not keep the engine battery topped up and then energise the relay to keep the domestics topped up?

 

Any thoughts?

 

Nick

 

 

When I leave my boat for a period of time...with only solar....I link both battery banks with some jump leads.

[Detling]

I have heard that a old incandecent light bulb in series with a 5amp diode between domestic and started will act as a trickle charge. You could probably use a 10ohm power resistor instead of the bulb, it is just to limit the current when starting the engine and the starter volts drop to about 10 volts the diode stops the domestics getting any power from the starter.

 

[MtB]

2 hours ago, Detling said:

I have heard that a old incandecent light bulb in series with a 5amp diode between domestic and started will act as a trickle charge. You could probably use a 10ohm power resistor instead of the bulb, it is just to limit the current when starting the engine and the starter volts drop to about 10 volts the diode stops the domestics getting any power from the starter.

 

 

I guess it would, but I'm not sure why the diode. 

 

Or as others have suggested, link them with a jump lead if a flat starter batt is a problem. Or better still, trace the current drain. 

[Theo]

I think  that jump leads may be the way to go, but I must test the starter battery.  The whole set is very old!

 

Thanks for all the help.

 

Nick