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enter image description hereI have built a solar car by myself, but I can't let my battery get fully charged. I use four 12V batteries as a 48V battery, and I use 3 solar panels. Each have 19V, 18V at early morning and dusk, and 20V at noon. It can charge pretty quickly. I got 5.5A at noon. Battery is 48V 32Ah. It works great. It can run 15km every day using the free energy.

But it seems the battery can not be fully charged. Should I add a solar panel? Can I use 76V or 72V to charge a 48V battery?

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  • \$\begingroup\$ I forgot to say I use 3 panel Concatenation and use a 48v solar controller which output 58volt. Need answer Thank you. \$\endgroup\$ – Bill KKK Apr 15 at 9:01
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    \$\begingroup\$ Welcome to EE.SE! Schematic is king here. Please draw one or a block diagram of your setup. \$\endgroup\$ – winny Apr 15 at 9:05
  • \$\begingroup\$ How and what should I do to charge my 48v battery currently? Plz help thank you. \$\endgroup\$ – Bill KKK Apr 15 at 9:07
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    \$\begingroup\$ There is an image upload button on the edit dialog. Put all the information in the question, not in the comments. Please re-read what you wrote in the title and use full stops at the end of sentences instead of commas. 'V' for volt, not 'v'. \$\endgroup\$ – Transistor Apr 15 at 9:11
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    \$\begingroup\$ I imagine a lot of Americans will get their panties in a bunch over your nickname. \$\endgroup\$ – pipe Apr 15 at 11:06
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Since you aren't mentionning any battery failures, I am assuming you are talking about lead acid batteries. Otherwise you would have had some kind of constant current charging strategy.

But two things you need to realize are: the charging current will be proportionnal to the voltage difference between the output of your pannels and the voltage of your battery, the charge voltage for a single battery should be around 15.5-16V, in your case 64V total.

Thus your solar setup barelly reaches the target charging voltage, this explain the poor charging of your batteries.

On the other hand, 4 panels in series would be to high a voltage for your battery pack, thus you will have to convert your PV voltage down to 64V DC in order to get the proper charging current (which would in theory fully charge your battery).

This is the crude way of doing it. In home/industrial PV setup one usually want maximum efficiency. In this case you will implement an MPPT (maximum power point tracking) strategy in your power conversion system. That would insure that maximum power is drawn fron the PV regardless of the voltage/current, and power is converted back to the voltage needed in a second stage (in your case 64V). But this is slightly more complicated to do. You might want to look at this for a future upgrade.

What I would recommend you to do, is to find a good 76V to 64V regulator (or close to that), plug your solar panel on one end, your battery pack on the other end, and that would do the trick for a barebone PV battery charger.

But please be careful, and do your homework before trying anything that might cause damage to your vehicle, yourself or others. Fire is sometimes overlooked when working with electricity.

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  • \$\begingroup\$ I used to use mppt controller,it's too low efficiency .1.4a for 200w solar panel. I just connect my battery to solar panel simplely (see the pucture). now can get 5.8a at noon 12 oclick for 300w solar panel.thank you for answering.can I use a Voltage booster.make 58-60v to 64v? How efficient is it. \$\endgroup\$ – Bill KKK Apr 15 at 11:09
  • \$\begingroup\$ You can use a step up converter that's correct. It can have up to 85-90% efficiency, but finding one that will handle 300W will be either very costly or extremelly challenging to design. But it should be feasible. If thermal management and components are designed carefully. But stepping down the voltage unfortunatelly has the same power/heat issues than stepping up, and only slightly better efficiency. I am suprised that using an MPPT controller did not yield better results. It should in theory maximize the power density of your panel by adjusting the voltage at which its drawn. \$\endgroup\$ – benguru Apr 15 at 12:26
  • \$\begingroup\$ Very helpful,I will give it a try and let you know. \$\endgroup\$ – Bill KKK Apr 15 at 14:32
  • \$\begingroup\$ Well if you want a reliable controller, buy Morningstar or Midnight Solar. Once. \$\endgroup\$ – Harper Apr 15 at 22:15

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