6 watt solar feeding 12 volt battery

[Buck Parrish]

I have a supplemental 12 v deep cycle marine battery feeding a 2000 watt inverter, a 450 watt inverter and various 12 v lights.
I have an onboard charger to charge the 12 volt deep cycle marine battery.
It's not connected to the starting battery or generator/alternator.

Soon after I installed a 6 watt solar trickle charger my on board charger quit working. I don't think it was immediate, but not sure how long it was before it quit working.
The lights come on but the charging mode light does not.

All the wires are connected to the marine battery. All the time. via fuses / switches

Do you think the solar panel is confusing the automatic on/off sensor on the onboard charger?
Or do you think the 6 watt solar panel fried a circuit on the onboard charger?
Perhaps it was a coincidence ?

My onboard charger is relatively new. It's a dual bank on board marine charger. 'Pro Sport 8'
Both leads two blacks and two reds are tied together to feed the one battery (bank) as suggested by the manufacturer.
Any input would be appreciated, thanks.

 

[augie47]

Does the onboard charger start working again when you disconnect the solar ?
Guys who are familiar with the internal circuitry can better inform you than I can, but I have seen similar situations where the output of one charger is at a level where the alternate charger thinks the battery is fully charged, based on voltage, and shuts off.
With my situation nothing "fried" thankfully.

 

[Buck Parrish]

Does the onboard charger start working again when you disconnect the solar ?
Guys who are familiar with the internal circuitry can better inform you than I can, but I have seen similar situations where the output of one charger is at a level where the alternate charger thinks the battery is fully charged, based on voltage, and shuts off.
With my situation nothing "fried" thankfully.

I've not tried unhooking the solar panel , yet. But I will and get back to you. thanks

 

[GoldDigger]

Since the open circuit voltage of the "12V" solar panel will be greater than 18V, be careful never to connect the panel to the charger output without the battery also connected in parallel.

 

[Buck Parrish]

Since the open circuit voltage of the "12V" solar panel will be greater than 18V, be careful never to connect the panel to the charger output without the battery also connected in parallel.

Yes, they're always connected. I'll try what Augie suggested tomorrow. I'll let you all know if it worked, surely I'm not the first one to try this. Any one with a large boat or RV are likely using a solar trickle charger, If not, they likely will. We'll get all the kinks worked out eventually.

 

[ggunn]

Is 6W DC STC even enough to overcome the self-discharge of the battery?

 

[MelvinTrousdale]

I have a supplemental 12 v deep cycle marine battery feeding a 2000 watt inverter, a 450 watt inverter and various 12 v lights.
I have an onboard charger to charge the 12 volt deep cycle marine battery.
It's not connected to the starting battery or generator/alternator.

Soon after I installed a 6 watt solar trickle charger my on board charger quit working. I don't think it was immediate, but not sure how long it was before it quit working.
The lights come on but the charging mode light does not.

All the wires are connected to the marine battery. All the time. via fuses / switches

Do you think the solar panel is confusing the automatic on/off sensor on the onboard charger?
Or do you think the 6 watt solar panel fried a circuit on the onboard charger?
Perhaps it was a coincidence ?

My onboard charger is relatively new. It's a dual bank on board marine charger. 'Pro Sport 8'
Both leads two blacks and two reds are tied together to feed the one battery (bank) as suggested by the manufacturer.
Any input would be appreciated, thanks.

Using these panels is very complicated..It is the reason I dont preffer them.. Hope you have found the right solution till now..

 

[jaggedben]

Since the purpose of trickle charger is typically to leave a setup alone and avoid the need for an outside power hookup, I'm not sure why you have both hooked up. Also, it's generally not a great idea to have two chargers charging the same battery unless they are designed to work together. (E.g. a generator/utility charger as a backup that only turns on if it senses that the PV charger does not have power available.)

I'm not clear from your description if the solar panel comes with a charge controller or not, but it should definitely be used with one.

 

[Buck Parrish]

I didn't think of the solar trickle charger until I had already installed my onboard 120 v charger. I installed a toggle switch between the solar charger and the battery for when I am using the 120 v charger.
The trickle charger works fine. The only time I need to use the 120v charger is if I am using the 2000 watt inverter a lot. Then I open the circuit to the solar the toggle switch. It seems to be okay now. But if I get a bigger solar panel. I will definitely put some type of control on it.

 

[cadpoint]

Go forward with the thought that most chargers output are above the base line output of the product your charging, IE if it's a 12 V battery then it'll be 14 V's output to charge.

It's no different than a battery charger for a golf cart, the charger sends out a minimum of 14V for a 12V
battery. It technically goes higher at first and comes down as the circuit is read for the exact need of a continual charge.

Again it's no different than watching the dials on the dash of a Car or Truck. It'll display charging at 14V
all day and all night with a good battery, and associated belts...

I can't figure out the 6V output and the other interfacing your doing!

 

[gar]

141018-1140 EDT

Some guesses based on practically no information.

Assume for simplicity that the solar panel can be represented by a voltage source, Vs, and an internal resistance of Ri.

Using GoldDigger's 18 V and the original post maximum power of 6 W, then the value of Ri is 6/9 = 2/3 A. If the battery has 100 ampere-hours capacity, and self discharges in 60 days, then self discharge is 60*24*Is = 100, or Is = 0.07 A. Multiply by 4 (assuming 6 hours charge time per day), and to equal self discharge requires 0.3 A from the solar panel. Thus, more than enough average current to exceed self discharge. Need actual values instead of my guesstimate.

The battery won't be damaged by the solar alone. However, one could add to the solar source a series current limiter (constant current device).

If you are worried about excess voltage backfeeding another charger, then add voltage limitation to the solar. When the battery is connected it serves the purpose of limiting voltage.

.

 

[GoldDigger]

cadpoint: All I have seen mentioned is 6 watts. Where did you get 6 volts?

 

[GoldDigger]

gar: I think your math is a bit backwards.
100AH divided by 60 days is 1.67AH per day. To match that 1.67AH in four solar hours the panel needs to produce just over .4A at max.
If the panel delivers its 6 watts at 18V, that would be only .33A, not enough to keep up with self discharge.
In a northern winter with only 2 solar hours per day, it would be even worse.

 

[gar]

141018-2410 EDT

GoldDigger:

In post #4 you mentioned an open circuit voltage of greater than 18 V. And I used 9 V for the maximum power point to the load based on 18 V. Not very accurate because the equivalent circuit I assumed is not correct, but it gives some sort of ballpark figure.

.

 

[GoldDigger]

Actually if the panel follows the common pattern for battery charging panels, 18V would be the maximum power voltage and the open circuit voltage would be closer to 23 volts.
If the panel is instead designed specifically for use without a charge controller, the maximum power voltage might be as low as 14V.
There would be no point at all to a Vmp of 9 volts since the battery voltage would never drop that low. I would be hard pressed to justify a Vmp any lower than 12 volts, and in any case the current will drop sharply as the voltage rises above Vmp and to offset self discharge the terminal voltage will have to be 14V or even higher.

 

[cadpoint]

cadpoint: All I have seen mentioned is 6 watts. Where did you get 6 volts?

Actually if the panel follows the common pattern for battery charging panels, 18V would be the maximum power voltage and the open circuit voltage would be closer to 23 volts.
If the panel is instead designed specifically for use without a charge controller, the maximum power voltage might be as low as 14V.
There would be no point at all to a Vmp of 9 volts since the battery voltage would never drop that low. I would be hard pressed to justify a Vmp any lower than 12 volts, and in any case the current will drop sharply as the voltage rises above Vmp and to offset self discharge the terminal voltage will have to be 14V or even higher.

I have no defense and read right pass it, I have no excuse! But hey you only answered in Volts!

 

[gar]

141019-1706 EDT

I should not have used the approximation approach I used above. Rather it is better to assume the 6 W PV panel was designed to be in its constant current region when charging a 12 V battery. Assume 12 V and 6 W (you could choose to use 13 or 14 V instead), then the current at 12 V is 0.5 A.

My son had bought a 1.5 W 12 V charging panel a number of years ago with which to play. Never really used it. I brought that home late this afternoon. The rating is 22.5 V 1.5 W and maximum output current 0.125 A. The voltage calculated from 1.5 W and 0.125 A is 12 V. This scales to 0.5 A for Buck Parrish's unit. Not far from my original estimate.

The open circuit voltage on my son's 1.5 W panel in late afternoon hazey sunlight today was about 20.5 V, short circuit current 0.03 A, and about the same current to a 12 V battery. My son also has a 5 or 6 watt solar charger for his boat lift battery, no other power on the dock, good. The 5 or 6 W solar panel is enough to keep the battery charged for weekend used. Probably not sufficient for daily use of the lift.

When the sun is bright I will retest the 1.5 W panel.

.