Dual Battery System with CTEK D250 not charging battery over 12 volts.

john61ct

Adventurer
Use the Blue Sea Circuit Wizard app to size wire. Higher voltage from the panels reduces the need for heavy copper, better to get a dedicated MPPT solar controller for flexibility.

Keep the SC near the target bank.

The ds250 is an mppt control. Buying a separate mppt solar controller is a waste of money. No reason to spend a couple hundred bucks for a programmable controller for a 100w panel.
My point was that **if** you want to take advantage of high PV volts to let you put panels far from the van, **then** you would want a better dedicated controller rather than the (IMO afterthought) built into the DCDC.

Here a Victrom MPPT that can handle over 60V input is under $80.

Apples to apples far better output than the CTEK in any case, fully adjustable and full logging graphs with a dongle or PC connection etc.

Proper heavy copper over long distance is awkward and more expensive.
 

john61ct

Adventurer
Well you wouldn't pipe the output from another SC into the panel inputs, not harmful but wasteful .

WRT the DCDC part, it's just electricity input, can come from any type of charge source or multiple ones concurrently.

I agree that people who want a robust solar setup may be better off with a different DCDC unit, the CTEK is fine, but at the price pretty limited compared to say the Sterling line.
 

jacobconroy

Hillbilly of Leisure
I was going to give the solar panel a charge during a trip this weekend, but I haven't ordered a solar controller yet. Is it going to fry my AGM if I charge it with 18 volts DC? Doesn't sound like a good idea to me.
 

dwh

Tail-End Charlie
I was going to give the solar panel a charge during a trip this weekend, but I haven't ordered a solar controller yet. Is it going to fry my AGM if I charge it with 18 volts DC? Doesn't sound like a good idea to me.

It isn't going to charge at 18v. Directly connected, the solar panel will operate at whatever the battery voltage is.

If left connected long enough, the panel could theoretically drive the battery voltage up to 18v. Eventually. Maybe...before the sun goes down. But it would be fighting against an ever increasing battery resistance the whole time.

So it probably will never get the battery all the way up to 18v. But it could get it up above 15v, and depending on temperature, that could easily be too high.

So it's a bad idea.
 

Mccaf

Adventurist
It isn't going to charge at 18v. Directly connected, the solar panel will operate at whatever the battery voltage is.

If left connected long enough, the panel could theoretically drive the battery voltage up to 18v. Eventually. Maybe...before the sun goes down. But it would be fighting against an ever increasing battery resistance the whole time.

So it probably will never get the battery all the way up to 18v. But it could get it up above 15v, and depending on temperature, that could easily be too high.

So it's a bad idea.

DWH, Thanks for the input - important Stuff. Your posts "everywhere" carry some weight imo.

So I have a basic solar panel electric wiring question.
Lets say the RENOLOGY 100w panel is wired with 14g wire to the MC4 connectors.(should be a few inches from the panel to the connector- no controller)
I would connect the 50' RUN of 10g wire to my DS250.

Q: Will the 14g to 10g cause me any loss of voltage/amp output from the panel to the battery?
 

john61ct

Adventurer
Yes the larger gauge for long runs, stepped down to lighter gauge at the ends, is bog standard and often unavoidable.

But each connection adds some resistance increases required care and maintenance checks over time, voltage drops, power losses to heat, safety issues etc.

So minimize as much as possible.
 

dwh

Tail-End Charlie
Q: Will the 14g to 10g cause me any loss of voltage/amp output from the panel to the battery?

A. Nah.



50' of #10 will have less resistance than 50' of #14. But that resistance depends on load - often characterized as "voltage drop" (but actually, in this situation, it's the amps that would drop, not the voltage).

With MPPT, the solar circuit will operate at Vmp, which is ~18v. 100w ÷ 18v = 5.5a. Hell, at 5.5a you could use 50' of #14 and not see a noticeable reduction in amps.

So you don't actually need #10. It would be a different story if you had a couple hundred watts of solar and the 50' run was carrying 15a-20a.

As for the slight added resistance of the connection of the #14 to the #10 - the reduced resistance of the #10 will make up for that. And...you'd have that anyway even if you connected the #14 to more #14.


But again, with MPPT there are TWO circuits - solar side and battery side - operating at different voltages/amperages.

So while
100w ÷ 18v = 5.5a
on the solar side...

100w ÷ 14v = 7.1a
on the battery side...

So depending on the size of the solar and the distances, a wire size that would be fine on the solar side might be too small on the battery side.


But not in your case. Even 7.1a isn't enough to worry about needing to upsize wire.
 

Mccaf

Adventurist
The precise answer is yes, but that loss will be insanely small...
Fuggitabodit :coffee:
Thanks. 10/4 check that box.

Yes the larger gauge for long runs, stepped down to lighter gauge at the ends, is bog standard and often unavoidable.
But each connection adds some resistance increases required care and maintenance checks over time, voltage drops, power losses to heat, safety issues etc.
So minimize as much as possible.
Thanks. Copy the P/M and Resistance


A. Nah.

50' of #10 will have less resistance than 50' of #14. But that resistance depends on load - often characterized as "voltage drop" (but actually, in this situation, it's the amps that would drop, not the voltage).

With MPPT, the solar circuit will operate at Vmp, which is ~18v. 100w ÷ 18v = 5.5a. Hell, at 5.5a you could use 50' of #14 and not see a noticeable reduction in amps.

So you don't actually need #10. It would be a different story if you had a couple hundred watts of solar and the 50' run was carrying 15a-20a.

As for the slight added resistance of the connection of the #14 to the #10 - the reduced resistance of the #10 will make up for that. And...you'd have that anyway even if you connected the #14 to more #14.
But again, with MPPT there are TWO circuits - solar side and battery side - operating at different voltages/amperages.
So while
100w ÷ 18v = 5.5a
on the solar side...

100w ÷ 14v = 7.1a
on the battery side...

So depending on the size of the solar and the distances, a wire size that would be fine on the solar side might be too small on the battery side.
But not in your case. Even 7.1a isn't enough to worry about needing to upsize wire.

Damn DWH, I just spent 30m deciphering that! Shows me how much I need to learn about this, ahhaha... Your explanations as usual are, sound spot on.

Question: MPPT? maybe I should toss it in the package with the panel and the MC4s. when I order. I already installed a CTEK D250s. which limits the input at 20amps total.
Why is MPPT better?

I also plan on adding another 100w panel, as needs grow, say 200w total next year as needs permit, adding another 100ah batt...

So, resistance, ****** that? 10ga wire it is.
 

dwh

Tail-End Charlie
The 250s has an integrated MPPT solar charge controller. Limited to 22v on the solar input so don't get a panel with a Vmp rating higher than 22v.
 

john61ct

Adventurer
To be safe use Voc to give a little headroom, I use 10-15%.

Cold bright mornings, snow / cloud reflection, don't want to fry that pricey gadget.

When you expand, Victron MPPT gives a lot more efficiency and flexibility, lower-amp models around $100.

Cheap enough you can dedicate a SC per panel, best solution to partial shading, don't need to exact-match panels later.
 

coolfeet

Mark Keeler
CTEK replaced my D250s free of charge. I exhausted all other resources. The unit was faulty! Hopefully, 3 years of struggling is over!
 

Mccaf

Adventurist
As I am writing this, I have my vehicle parked in full sun shining on the 160 watt solar panel. The battery was at 12.75 volts before I started charging with the solar panel. After 5 hours of charging, it's at 13.2 volts. I do not have any appliances connected to the service battery.

So, third time thru this thread....are you saying this is normal rate of charge after 5 hours? Taking into consideration your DS250 was a bad unit.... I’m not sure what IS normal rate of charge.
 
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