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Charging LiFePO4 Batteries


ebrsa
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In our village we have a CCTV monitoring system, installed and maintained by a few residents of which I have been one since we started it some 13 years ago. Some of our cameras run off 12V 100AH batteries, charged by the street light power which is only on during night hours. Thus far we have used SLA batteries with disappointing lifespans. We now wish to install LiFePO4 cells with a BMS and add solar panels with charge controllers to boost power during the day.

Since the charging characteristics of LiFePO4 differs from SLA, I have been trying to find suitable mains chargers and solar charge controllers. So far it would seem that the Victron IP65 may be a suitable mains charger. Of course the less costly the better. Any advice and suggestions for mains chargers and solar charge controllers would be much appreciated. @___ (I guess this is you plonkster) perhaps you would have some suggestions.

 

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If cost is an issue you could always grab a laptop 100W+ PSU, they output 19V mostly, then put that through a DIY circuit that allows Constant Current & Constant Voltage in either Buck/Boost depending on your voltage. Something like this item from banggood, you might need to get a computer fan mounted on it depening on the current setting. If DIY Circiut is not your thing then option 2 would be to get a cheap solar pwm charge controller that allows 19V input and charge from the laptop output.

You can also just get a normal PSU like this 24V Switched mode power supply if you do not have an old laptop PSU lying around.

What is your power requirement from the battery between charge cycles? how many AH do you use between charge cycles?

What lithium cells do you plan to use?

 

 

Edited by iiznh
thought of another option
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@iiznh Thank you for your suggestions. After checking the specifications of our present charger and solar pwm charge controller, it would seem that we will stay within the limits of LiFePO4 batteries. We will be using 100AH cells with a Daly BMS. As we will be adding a 73W 12V solar panel to the system, it should keep the battery at a high SOC during the day until the street lights come on and mains charging takes over. The Victron IP65 and a Victron MPPT solar charge controller would be ideal but is also quite pricey. 

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You did not answer what you power usage will be? If you do not know that is fine, then maybe tell me what equipment you need to power.

I assume you are adding 4 cells. Thus 3.6V X 100ah = 360Wh of energy per cell thus 1440Wh fully charged. That is a lot of power way more than what you would need.

How much power does you cctv camera use? mine uses about 12W and let us assume the longest days of about 14 hours that would take 168Wh from the battery hardly 11 percent. Adding a solar panel would simply add more unnecessary cost to you build. 

So let us assume 12W power required for the moment. (wondering how do you connect the data feed, wifi maybe)

I personally would rather use some of these 32700 6AH cells you will need at least 8 of them to cover the 168Wh requirement. Let us rather be safe and select 12 of them... in a 4s 3p configuration which should give you about 260Wh to work (batteries will degrade slightly over time so budget for that too) with with a small Daly 10A BMS, DIY charging circuit, 10A Automotive fuse the whole backup system should cost about R1600 and should run the cameras easily for 14 hours between charges. Since you are not draining the batteries to 0% they should also last longer. Now I am not sure if Yzerfontein gets sub zero temps during winter since that could potentially be bad for the batteries. They do not like to charge when it is close to freezing point

Provide more info, little projects like these are real fun to build

 

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@iiznh We are using about 40W for a Ubiquiti Powerbeam, 1 x LPR camera with infrared illumination, 1 x CCTV camera and a network switch. Also we have an infrared illuminator using about 60W at night. Our mains charger current is only 7.2A so I guess we never did manage to charge the battery fully. We are going to disconnect the infrared illuminator as the LRP camera's built-in infrared illumination is sufficient for reliable number plate recognition.

Thanks a great deal for your suggestions.

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Seems like a large mismatch between power requirements. The Ubiquity uses about 10W according to the spec sheet.

Day: 15W LPR Camera + 10W Ubiquity P2P Wifi + 12W CCTV Camera + 8W Network Switch = 45W

Night: The same as above + 60W IR illuminator so roughly 105W.

Your charger was supplying 7.2A X 13.8V = 100W at night... not enough to drive the system and charge the battery

Your panel is supplying 73W max, I hope that the voltage is at least above 12.8V otherwise it will not charge the battery. On a good day you might get 60-72W for a couple of hours (4 hours) assuming full sun and a clean panel.... but if it is cloudy or there are shadows you will get almost nothing, the voltage will be too low to charge the battery. There will be several hours where the battery alone should supply 45W (about 4A)... During peak sun there might be 20-33W of additional power to charge the battery but only in ideal situations (and that does not take into account any losses in the system).

At night your battery will slightly discharge and during the day quite a lot, the slightest bad weather will cause a large drop. Switching to Lithium batteries will not solve the problems unless you calculate your power requirements carefully. 

You existing design would kill any battery, regardless of chemistry

We are all here to learn so update the thread with useful info and hopefully other people would be able to learn from your mistakes

 

 

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