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agim avatar image
agim asked

Charging problems

I have problem to charge six 2v batteries connected serial that give 12 v . There are 270Ah batteries. I have MPPT 75\15 charger. Since I am from Montenegro we have a plenty of Sun. OK not this year but still in cloudy weather I get 15.16v from solar panel on sunny it goes up to 20v . I use this for charging batteries for sea light that has 20w light. Still my battery drains. This sea light is not close to me so I can not check it regularly but it happens on 15-16 v from solar to not have charging at all. What is the problem. I do not have a bluetoothe dongle. Please help I am tired of driving to sea light once a week to charge drained batteries with generator

battery charging
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3 Answers
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ejrossouw answered ·

Hi @Agim

"The controller will operate only if the PV voltage exceeds battery voltage (Vbat).

● PV voltage must exceed Vbat + 5V for the controller to start. Thereafter minimum PV voltage is Vbat + 1V."

In light of this you need 17V to get the charging started. Best option is to add another panel in series or if you have 2 already in parallel, connect them series.

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Justin Cook avatar image Justin Cook ♦♦ commented ·

I'll add - minimum 17v to start charging... in reality, a 12v nominal battery will usually be between 12.2 - 13.2v, so it'll require 17.2-18.2v from PV to start charging.

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agim answered ·

If I understand well practically I need 17.5v every day to charge battery so if I have 16v on cloudy day with battery 11.5 v it will not be charged that day. If it is like that all stories about better harvesting with mppt solar charger a just marketing because my solar panel will charge battery on 14v without mppt charger if the battery is for example at 11v. I just need mppt charger for protecting battery. Am I wright

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ejrossouw avatar image ejrossouw commented ·

Not exactly. It only requires the initial 17.2V to "start up" the MPPT and thereafter 13.2V min to keep it going. Overall the MPPT is much better at harvesting energy and definitely a good investment, but PWM still has it's place depending on the requirement. Just add another panel if feasible and you will never look back.

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ejrossouw avatar image ejrossouw commented ·

"It is generally accepted that MPPT will outperform PWM in a cold to temperate climate, while both controllers will show approximately the same performance in a subtropical to tropical climate."

Solar and batteries are typically more complex than just the headline grabbing features. The above extract is a from a Victron document, which could have helped, although may not have flagged the +5V startup aspect. From it you will see MPPT favours higher voltage than PWM for various reasons. Not sure where the protection idea came from. Why did you want to upgrade in the first place? IMHO, PWM will continue to serve people well so no reason to not revert back if another panel is not an option.

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agim answered ·

@ejrossouw thanks for your help. Thanks to you I understand where is my problem and that unfortunately I have wasted money by buying 4 mppt 75/15 . You have written a long story but I still did not catch do pwm charger has 5v difference for intial starting of charging and do the other Chinese products have the same. Just short please . It will help me decide to buy new chargers or to continue like this. About explosions it happen two times in 5 year experience and far away from people. We saw it after sealite stoped working mostly just batteries stop working faster.

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klim8skeptic avatar image klim8skeptic ♦ commented ·

Has no one mentioned adding another (similar speced) solar panel in series with your existing panel?

That will give you enough voltage for the mppt to start reliably, and give you twice the charging input for really cloudy days.

Much cheaper than changing the regulator.

Don't go over the mppt voltage limit of 75 volts. (pv input)

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Matthias Lange - DE avatar image Matthias Lange - DE ♦ klim8skeptic ♦ commented ·

In the first answer @ejrossouw already mentioned to use two panels in series.

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agim avatar image agim klim8skeptic ♦ commented ·

Can you please just answer my question ? Its much easier to put new charge controller then to take sollar panel on the island and to mount it on the top of sealite.

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ejrossouw avatar image ejrossouw commented ·

No, PWM does not have the vbat +5v startup requirement. It will however depending on the device specification typically charge at 13.6v if charge values are not adjustable, but I cannot comment on budget devices otherwise and suggest you youtube pwm reviews.

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agim avatar image agim ejrossouw commented ·

Thank you very much sir ! I will by quality one but I planned to by cheap one if quality one still has 5v initial difference . Thank you very much once again . This topic can be closed. :)


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