Another daft One Two Both switch question

[webcraft]

I have wired two solar panels and an MMPT up to the domestic bank.

If I set the switch to Both occasionally during the day will the solar charge the engine start battery as well?

(Please don't tell me how useless/stupid/inefficient a One Two Both switch is - I have read all that but it is what exists)

 

[Sandy]

Yes.

 

[PaulRainbow]

I have wired two solar panels and an MMPT up to the domestic bank.

If I set the switch to Both occasionally during the day will the solar charge the engine start battery as well?

(Please don't tell me how useless/stupid/inefficient a One Two Both switch is - I have read all that but it is what exists)

It will, but while the switch is in the both position you could discharge both batteries. Why not fit a VSR instead ?

 

[Hoolie]

If I set the switch to Both occasionally during the day will the solar charge the engine start battery as well?

A bit or not depending on sunlight. Why don't you do as Paul has suggested and fit a VSR? They are neither expensive or difficult to install in place of a 1-2-both switch.

 

[MontyMariner]

If you had bought a two output solar reg, you wouldn't have had a problem!

 

[William_H]

IMHO a VSR used for batteries being charged by small solar would not work well. The first battery may well not reach the 13.5 v or so to connect to the second. (dependent on sunshine, panel and battery size.) Plus the current drain of the relay if it operates may well negate much of your small charge.
I would suggest an additional small PV panel (less than 10w ) connected directly to start battery. You could buy an additional controller but not really necessary for small panel.
Or buy another similar MPPT controller and run off the PV panels in parallel or divide the 2 panels so one for each battery and controller.
The idea of occasionally going to both to boost the engine battery is ok if you are on the boat and are diligent about turning to off when leaving the boat or after a while. In fact going to both will make the domestic battery charge the engine by connecting both together so may get a rapid boost regardless of solar charge.
In any case it is desirable to switch to off when leaving the boat. ol'will

 

[Refueler]

My small panel on Superanne feeds to a dual output controller ... one goes to batt A .. other goes to batt B.

The panel may only be small and then divided across two batterys - but it works. No need to consider paring the batterys to get charge ..
It will never keep up with on-board useage ... but when boat is moored and not in use - it quietly maintains .
I do have a second same panel with controller and because first works - I am thinking to add this second one and then dedicate each panel to own battery.

 

[GHA]

or...
dual voltmeter to keep an eye on both banks, another digit would be better though. Start battery likely won't get discharged starting the engine, just self discharge sitting around doing nothing for a few months.
Then if the main bank is up over 14v under a good days solar you could flip the 12b to combine for a little while til you motor again.



Voltmeter straight onto the terminals easily visible from your favourite seat is an excellent thing on a cruising boat

And if you really want to know the SOC of the main bank one of these > (which will measure voltage of a second battery as well)

 

[Pye_End]

I have wired two solar panels and an MMPT up to the domestic bank.

If I set the switch to Both occasionally during the day will the solar charge the engine start battery as well?

(Please don't tell me how useless/stupid/inefficient a One Two Both switch is - I have read all that but it is what exists)

Depends.

If your domestic bank is low, and poor light conditions or small solar etc., the engine battery could charge the domestic.

Similarly, if the engine battery is low, and the domestic well charged, then the domestic could loose charge to the engine battery.

If you have a similar state of charge in both batteries, and decent solar, then the solar will charge both.

Why does the engine battery need a solar boost? Takes little capacity to start an engine, which it should give back in short time from the alternator.

 

[Aja]

Buy a second small panel as @ol'will suggests just for engine battery. Fit and forget. 20w will be quite enough to keep battery topped up.

 

[webcraft]

Am thinking will just go with using the alternator to keep the engine start battery topped up.

That works fine on the Portuguese boat.

 

[Aja]

Save the wear and tear on your starter motor and engine and not waste fuel.

Fit something like this and forget about it.
Solar panel - Amazon for about £20

 

[webcraft]

Save the wear and tear on your starter motor and engine and not waste fuel.

Fit something like this and forget about it.
Solar panel - Amazon for about £20

I am only going lot be using the alternator to charge the engine battery because I need to use the engine.

 

[Refueler]

My top-up panel is a cheap ebay job fitted to a ply sheet - pipe clips to pushpit rail ... comes with cable, USB, PWM controller (works fine) .. see photo :

As long as nothing is on .. that panel will trickle along ....

 

[B27]

Am thinking will just go with using the alternator to keep the engine start battery topped up.

That works fine on the Portuguese boat.

Works fine in season for me too.
Over winter, a small panel kept an aging engine battery topped up, when the engine wasn't started for 3 weeks at a time.

 

[riverliver]

For what worth based on the great advice on this forum i have a couple of small 20v panels with an MPPT controller for them to charge the domestic engine and a smartguage (Merlin) as advised at post 8 and it has worked a treat over the winter in keeping the batteries topped up and cost not much at all and didn't need to strain my electrical skills beyond connecting a few wires. Understand the pushback on 1B2 switch but hasn't caused me a problem so far.

 

[Sea Change]

Yes it will put the two banks in parallel and share the solar charging between them. Perfectly fine strategy if you're onboard and know that the house battery is full, and want to give the engine battery a little boost. But if you leave it set up like that, and have any loads on the system, you could end up draining your engine battery.

 

[Tranona]

Another thought, maybe a trickle B2B would be useful. You could then ignore the 1,B bit of your switch and just charge the domestic battery.
12voltplanet.co.uk/votronic-12v-standby-charger-trickle-charger.html

 

[GHA]

Another thought, maybe a trickle B2B would be useful. You could then ignore the 1,B bit of your switch and just charge the domestic battery.
12voltplanet.co.uk/votronic-12v-standby-charger-trickle-charger.html

Not a bad idea
Though you could get a buck boost off ebay for a fraction of the price.

 

[William_H]

Another thought, maybe a trickle B2B would be useful. You could then ignore the 1,B bit of your switch and just charge the domestic battery.
12voltplanet.co.uk/votronic-12v-standby-charger-trickle-charger.html

That so called B2b charge looks a bit to me like a simple diode connection. Note it says the charge voltage will be .6v less than supply battery so no boost and will only charge when supply battery is at a voltage indicating being charged. ie perhaps 13.75 v a voltage which the supply battery may nopt reach with small pv panel.
So a simple (schotke) diode with current limiting resistor would do just as well. ol'will