Voltage Drop on new solar panel installation

[Jaco.niekerk@hotmail.com]

I've finally installed solar panels on the boat.
I've 2x100w panels in series and ran 11m, 6mm wire to the MPPT controller.

I noted something odd. The voltage of the two panels in series come to 40-41V measured at the panels.
The voltage measured at the bare wires going into the controller is 40-41V.

However, once the charge controller is connected and starts doing its charging, the voltage drops to 30-34V.

Is this normal?

Comments appreciated

 

[DannyB]

I'm guessing what you are seeing is 40-41 v open circuit, with no current flowing, and 30 odd volts once the controller starts pulling current. In which case it's quite normal.

 

[William_H]

Presumably you are charging a 24v battery system. Hence you connected 2x "12v" panels in series. This correctly gives you about 40 v with no load. If you are using a cheap pulse width modulated controller or similar then this will effectively connect the panels directly to the battery until such time as the battery voltage reaches a full charge about 28volts or so.
If you try to measure the controller output with no battery connected you might get any voltage from 38 to 28 volts measured. Once you connect the battery then you measure the controller output which is also actual battery voltage which will be between 24 and 28 volts depending on charge rate (panel size) and battery charge state. So actually it is the current into the batteries that might be more indicative.

If on the other hand you have wired the panels in series but want to charge a 12v battery then you must have an MPPT type controller. Then again with no battery connected the voltage measured out of the controller we would hope would be around 14 volts but could be anything with no load. Again current into the battery is best indication.

Lastly do check your volt meter for reasonableness on a charged battery. Digital multimeters do over read if the battery is low. good luck olewill

 

[PaulRainbow]

Presumably you are charging a 24v battery system. Hence you connected 2x "12v" panels in series. This correctly gives you about 40 v with no load. If you are using a cheap pulse width modulated controller or similar then this will effectively connect the panels directly to the battery until such time as the battery voltage reaches a full charge about 28volts or so.
If you try to measure the controller output with no battery connected you might get any voltage from 38 to 28 volts measured. Once you connect the battery then you measure the controller output which is also actual battery voltage which will be between 24 and 28 volts depending on charge rate (panel size) and battery charge state. So actually it is the current into the batteries that might be more indicative.

If on the other hand you have wired the panels in series but want to charge a 12v battery then you must have an MPPT type controller. Then again with no battery connected the voltage measured out of the controller we would hope would be around 14 volts but could be anything with no load. Again current into the battery is best indication.

Lastly do check your volt meter for reasonableness on a charged battery. Digital multimeters do over read if the battery is low. good luck olewill

Will, he says in post #1 he has an MPPT controller.

 

[VicS]

I've finally installed solar panels on the boat.
I've 2x100w panels in series and ran 11m, 6mm wire to the MPPT controller.

I noted something odd. The voltage of the two panels in series come to 40-41V measured at the panels.
The voltage measured at the bare wires going into the controller is 40-41V.

However, once the charge controller is connected and starts doing its charging, the voltage drops to 30-34V.

Is this normal?

Comments appreciated

Yes it is what I would expect.

If you look at the tech spec for your panels you should find figures for some or all of the following

Open circuit volts .......... that be around 20 volts, or a little more, for a 12 v panel

Volts at maximum power (that should be where your MPPT controller is making them operate) typically around 16 to 17 volts for a 12 volt panel

Current at max power ..... for your panels that'll be about 6¼ amps

(Current at max power × volts at max power = the power rating of the panels)

Short circuit current .... which will be slightly higher than the current at max power


BTW it is not a smart idea to use your email address as your user name

 

[sailaboutvic]

Yes it is what I would expect.

If you look at the tech spec for your panels you should find figures for some or all of the following

Open circuit volts .......... that be around 20 volts, or a little more, for a 12 v panel

Volts at maximum power (that should be where your MPPT controller is making them operate) typically around 16 to 17 volts for a 12 volt panel

Current at max power ..... for your panels that'll be about 6¼ amps

(Current at max power × volts at max power = the power rating of the panels)

Short circuit current .... which will be slightly higher than the current at max power


BTW it is not a smart idea to use your email address as your user name

I hope he like plenty of junk mail .

 

[dom]

Presumably you are charging a 24v battery system. Hence you connected 2x "12v" panels in series...

AFAIK many manufacturers recommend connecting two or three panels in series in order to optimise both power transmission losses and the controller itself. E.g. the Victron 12/75 MPPT can nominally accept 3 panels in series.

The downside of this higher peak power potential is that a series connection risks the entire bank's output being seriously degraded in the event of a shadow, which is in practice why many folk choose parallel. So I'm not really disagreeing.

 

[Jaco.niekerk@hotmail.com]

I'm guessing what you are seeing is 40-41 v open circuit, with no current flowing, and 30 odd volts once the controller starts pulling current. In which case it's quite normal.

Thank you for confirming. Much appreciated

 

[Jaco.niekerk@hotmail.com]

Much appreciated.