4s Buck Down ?

UncleZeb

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Planning on upgrading/replacing some relatively old/tired batteries in my RC Baitboat i use for carp fishing/baiting up.
My boat has twin props, each powered by 2 x 7.4v li-ions, 1 x 12v lead acid for a Raymarine Sonar, 1 x 12v lead acid for
a wifi range extender, and 1 x 6v lead acid for a underwater camera winch system. Need to replace all the lead acids, which would reduce total weight drastically. Got acouple of hundred harvested 18650s that i can use, for something atleast. Will be buying new LifePos if necessary, if all else fails.

I understand the issue with 18650s and 12v setups, BUT, as i have loads of 18650s, wouldnt it be possible to overgun
a 4s buck down, for the 12v pack for the Sonar unit, which has the following power specs :-

Nominal Supply Voltage : 12vdc
Operating Voltage Range : 10.8v - 15.6v
Power Consumption at full brightness : 2.7w RMS

What about a 4s(6-10)p + buck down to 13v, balance charged to 4.0v max/3.0v min(16v/12v) ? Dont really need to
utilise the full capacity of the pack/each cell, so can overgun total capacity to compensate. I totally understand that LifePos ARE the easiest/most reliable solution, but we are talking about afew watts here, for the Sonar, and 5w max for the Wifi range extender amplifier unit.;)No powerwall specs required;)
 

daromer

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Will work fine. Might be better to even go to 7s to get better buck converters?
 

UncleZeb

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Cheers mate ...
Got acouple of these, spare, that i plan using :-
LM2596 DC-DC buck adjustable step-down power supply converter modules.

Whats the reasoning behind the 7s route ?
 

daromer

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4s at low voltage is below what you plan as output. You need to have some volts in betweem
 

UncleZeb

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7s would definately do the job, plus better bucks with a higher output(when needed).
These bucks have a 3A max rating. Lowest voltage @2.8/3.0(19.6v or 21v) still leaves alotta room, as the
min input for my specs/buck is 15v(13.5v + 1.5v(min).
 

Hyraelle

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Oh wow, i actually had this interrogation myself! And luckily i also have that same buck converter! I bought two some while ago just in case, and the case arose that i need to power a 12v water pump to water in a field. Now, i also ordered a 4s bms for this project, i just tought, i'll just leave a bottom in the battery. But since darometer mentionned 7s for voltage, would someone recommend me using a 7s bms in 5s to get 14~21 range?
 

floydR

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If you decide to use a 5s configuration get a 5s bms many lower end bms's have a set series that they are designed for.

later floyd
 

daromer

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Going for 5s is just odd. How do you plan to charge it. You need to look at the full chain :)
 

Hyraelle

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Going for 5s is just odd. How do you plan to charge it. You need to look at the full chain :)
Gna, you're right! i didnt think my hypothesis much! Maybe a labtop charger but even then its not right.

If you decide to use a 5s configuration get a 5s bms many lower end bms's have a set series that they are designed for.

later floyd
That also answer the question, will stick with the 4s one :)
 

UncleZeb

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I settled for 7s5p + 7s BMS´s + Buck downs, for my 12v packs, balanced charged with an ISDT Q8 BattGo 500W 20A
Charger/Discharger for 1-8s. Might seem overgunned, but fits well with my specs, taking overall capacity/Vdrop into account.
 
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