Battery maintenance via solar

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I have a 50w panel which maintains my house bank through a PWM controller. I have a second PWM controller which I am thinking of connecting to the 'appliance' output of the installed controller via its 'Solar in' terminals then supplying my engine batt from this. Any problems with this setup?
I know I can buy another panel or a dual battery controller but as I already have this kit I want to use it if possible. The charging is only to maintain the batteries when away from the boat so 50W is ample.
 
Forgive my simple approach ... but why not connect second controller to the solar same as the first ? Treat the two batterys separately ?

My thinking is that connecting a 'controller to a controller might be confusing for first controller ?
 
If you connect the new controller to the appliance output terminals of the first, then you are connecting to regulated voltage, which I can't see working. Although not recommended, originally I had 2 cheap PWM controllers connected to the same panels, one feeding each domestic bank and that worked well. Had to fit diodes in the feeds to them as found reverse current at night, enough to balance the banks.
 
Quiddle said:
I have a 50w panel which maintains my house bank through a PWM controller. I have a second PWM controller which I am thinking of connecting to the 'appliance' output of the installed controller via its 'Solar in' terminals then supplying my engine batt from this. Any problems with this setup?
I know I can buy another panel or a dual battery controller but as I already have this kit I want to use it if possible. The charging is only to maintain the batteries when away from the boat so 50W is ample.
Click to expand...
I think if you do o this you will have to experiment and monitor carefully to ensure that the system will work satisfactorily.
My suspicion is that feeding a second controller with the controlled output of the first will not be staisfactory

I think the way forward is to do as Graham has done and connect both controllers, via diodes if necessary, directly to the solar panel. I don't think that would work with MPPT controllers but I see no problem with PWM .

If you are preparing for a prolonged " coronavirus lockdown" a better solution might be to get the batteries home and maintain as necessary with a mains powered charger. I wish I had brought mine home instead of leaving connected to a solar charger.

I see batteries left for long unattended periods connected to a solar charger of "ample " capacity as something of a risk.
 
I think it is better to get a dual controller; you can apportion the share of the charge. Using the 'appliance' output is only subject to some 'spare' power, always assuming the second controller will work which I doubt like Graham.

At the risk of thread drift, can you explain the 'something of a risk' I have panels for a 24v bank and a panel for 2 x 12v bank with appropriate controllers and monitors. Everything has been working for 3 years with everything full.
 
Or for £20 you can get a small (20 or 25w) panel, controller & cables off ebay. Also, if it's of any use, a battery fully charged and in good condition, disconnected, will be fine to leave for a few months...
 
V1701 said:
Or for £20 you can get a small (20 or 25w) panel, controller & cables off ebay. Also, if it's of any use, a battery fully charged and in good condition, disconnected, will be fine to leave for a few months...
Click to expand...
But that's daft. Why have 2 panels, 2 controllers, and 2 sets of wiring? A 50w panel is plenty to keep both banks fully charged. Fitting a dual controller has to be the right solution.
 
The thing is I derive a strange satisfaction in parsimony, unrelated to the affordability of things. This eccentricity has only been exacerbated in the current clime.
 
Quiddle said:
I have a 50w panel which maintains my house bank through a PWM controller. I have a second PWM controller which I am thinking of connecting to the 'appliance' output of the installed controller via its 'Solar in' terminals then supplying my engine batt from this. Any problems with this setup?
I know I can buy another panel or a dual battery controller but as I already have this kit I want to use it if possible. The charging is only to maintain the batteries when away from the boat so 50W is ample.
Click to expand...

Do you not already have a split charge system (i.e. VSR)? I thought that was a mandatory requirement for these forums.
 
Thanks for the technical opinions, the two controllers off one panel is an interesting concept. Think I'll try various combos on a couple of iffy batteries at home.
 
With the possibility of a boat not being used or checked over the sunniest months, ISTM that the main risk might be overcharging.

Many solar controllers are really only designed around the idea of daily cycles.
If the batteries start out fully charged, all they need is a 13.7V float charge.
 
tillergirl said:
I think it is better to get a dual controller; you can apportion the share of the charge. Using the 'appliance' output is only subject to some 'spare' power, always assuming the second controller will work which I doubt like Graham.

At the risk of thread drift, can you explain the 'something of a risk' I have panels for a 24v bank and a panel for 2 x 12v bank with appropriate controllers and monitors. Everything has been working for 3 years with everything full.
Click to expand...

What I am thinking of is a situation in which you have a relatively small engine start battery being charged from a large solar panel that has been sized to charge a large domestic battery bank.
A 70 Ah battery and a 100W, or larger, solar panel perhaps

A 100 W solar panel will typically have an I max of around 5.75 amps. Normally of course once charged the battery will draw much less. If however the battery develops a fault such as a shorted cellthe current flow will increase. If this is sufficient to cause the battery temperature to rise you potentially have a run away situation which will end when the battery goes BOOM
 
lw395 said:
With the possibility of a boat not being used or checked over the sunniest months, ISTM that the main risk might be overcharging.

Many solar controllers are really only designed around the idea of daily cycles.
If the batteries start out fully charged, all they need is a 13.7V float charge.
Click to expand...

Long term at 13.7 volt will do the batteries no good, float charge comes from charging back-up batteries, i.e. telephone exchange, in the old days, they needed charging to a high voltage periodically.


Brian
 
Umm, thanks. I had planned to add temperature sensors - the banks are not small but the temperature sensors are not expensive.

I find the monitors very useful - hardly exciting but very useful.
 
halcyon said:
Long term at 13.7 volt will do the batteries no good, float charge comes from charging back-up batteries, i.e. telephone exchange, in the old days, they needed charging to a high voltage periodically.


Brian
Click to expand...
We float 12V batteries at 13.7V by the thousand. Have done for years.
For someone in the trade, you do talk some cobblers.
 
tillergirl said:
Because the controller is defective or just because they will overcharge?
Click to expand...
Many controllers start every day with a period of fairly high voltage.
A couple of hours a day of too much voltage adds up to drying out the electrolyte.
That carries a risk of one cell failing and a disastrous overcharging of what's now a 10V battery, but most likely it will just ruin the battery or shorten its life.
 
Quiddle said:
Thanks for the technical opinions, the two controllers off one panel is an interesting concept. Think I'll try various combos on a couple of iffy batteries at home.
Click to expand...


As my post #2 suggested - I think it is the simplest way to do it ... as to whether you need diodes I( think depends on whether you have services connected to one battery that could cause an inbalance of the batterys. If no services - then in theory you should get charged up on both and that should be it till one battery drops a bit ...
The Diode of course would need to be selected of a type to avoid the common voltage drop you can get of around 0.7V ....
 
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