# If i convert 24v battery to 12v op will it last longer than same ah 12v battery?

#### ddpwil35

Joined Feb 28, 2016
7
I am trying to come up with a battery system to supply an electronic fuel injection system on motorcycle engine powered race car that will weigh less and last longer while giving it greater reliability to last the entire race. I did a little research and found these LiFePo cells that I can make my own battery with just wondering if I could use a buck converter on a 24 volt battery that I made to make the battery actually last longer because I only need a 12 volt supply to run my equipment

#### ddpwil35

Joined Feb 28, 2016
7
This is a total loss system. I have no on board charging system due to engine rules. Any help would be appreciated. I already purchased 100 cheap 18650 cells, a couple balancing chargers, and other misc items to build the battery packs. I was just hoping someone here with more battery knowledge would have a tip on this build to save me a little R&D. I can configure battery any way it works the best. I just need a constant 12.1v-13v supply to last the entire race. Thanks gents

#### GetDeviceInfo

Joined Jun 7, 2009
2,194
It's all about the power. You can transform voltage and amps to get what you need, but in the end, you need enough power. id calculate with 100% duty. Don't let a failed battery charger prevent you from running the next round. What does that mean to capacity?

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#### ddpwil35

Joined Feb 28, 2016
7
So if I use a buck converter to take a 24v 10ah battery down to 12v 10ah with same load will the converted 24v battery last longer than the 12v battery unconverted?

#### Alec_t

Joined Sep 17, 2013
14,312
It would be more efficient (and save the weight of the converter) to build a 12V battery with 2N Ah capacity than to use a 24V battery of N Ah capacity and do the conversion. Same number of cells, different configuration.

#### GetDeviceInfo

Joined Jun 7, 2009
2,194
So if I use a buck converter to take a 24v 10ah battery down to 12v 10ah with same load will the converted 24v battery last longer than the 12v battery unconverted?
Yes, theorically twice as long, but as mentioned, less conversion efficiencies. Run a measured cycle on your cells. Cheap cells are notoriously 'cheap'. Series batteries are only as good as thier weakest cell. Boosting parallel cells may be more dependable. Combing series for voltage and parallel for current is the balance. Test your cells though to reduce disappointments at run time.

#### ddpwil35

Joined Feb 28, 2016
7
Thanks guys. I was really liking the converter idea too much I guess. I liked that the converters I was seeing had an led readout I could dash mount to monitor voltage status during the race. This will be our first year running a switched battery backup due to  as our former antigravity 16 cell battery was almost 300 a pop. I am now (thanks to power/tech savvy gents like you) able to separate fuel pump and ignition systems onto separate batteries, run a backup battery, and have 2 spare batteries ready to go in for the feature event with 0 at the track charging for the same \$ as 1 of my AG batteries with a weight reduction of 1.2 lbs! So general consensus is higher cell count 12v battery is the better option?

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#### ddpwil35

Joined Feb 28, 2016
7
I can do all that because of DIY battery packs I leaned about on the web. FYI

#### crutschow

Joined Mar 14, 2008
34,394
Thanks guys. I was really liking the converter idea too much I guess. I liked that the converters I was seeing had an led readout I could dash mount to monitor voltage status during the race.
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So general consensus is higher cell count 12v battery is the better option?
If you want a battery status indicator you can build or buy a circuit to do that. A small digital voltmeter could also be used.
But note that Lithium cells don't have the nice rolloff in voltage with discharge that lead-acid batteries do, so it's more difficult to monitor their state of charge.
They tend to maintain a constant voltage and then suddenly drop in voltage when they are near full discharge.

You definitely want to go with a 12V battery.
Any 24V to 12V converter will be less than 100% efficient so, for a given battery watt-hour capacity, your battery wouldn't last as long.

#### ddpwil35

Joined Feb 28, 2016
7
If you want a battery status indicator you can build or buy a circuit to do that. A small digital voltmeter could also be used.
But note that Lithium cells don't have the nice rolloff in voltage with discharge that lead-acid batteries do, so it's more difficult to monitor their state of charge.
They tend to maintain a constant voltage and then suddenly drop in voltage when they are near full discharge.

You definitely want to go with a 12V battery.
Any 24V to 12V converter will be less than 100% efficient so, for a given battery watt-hour capacity, your battery wouldn't last as long.
Thanks for helping me out! This forum is awesome

#### Dodgydave

Joined Jun 22, 2012
11,300
Can you not just use a 12V 7aH, or 10aH battery?

#### ddpwil35

Joined Feb 28, 2016
7
Yes I can build pretty much whatever value battery I want I guess I was just wondering if with the same amount of batteries configure two different way using the converter would I actually be taxing the batteries less to ensure a longer battery life or cycle before charging

#### Dodgydave

Joined Jun 22, 2012
11,300
Best to choose the best quality of battery that fits the job, with weight and capacity,.

#### Tonyr1084

Joined Sep 24, 2015
7,887
I have no experience or specific knowledge about a LiFePo battery. All I can say is that most batteries are considered dead when they reach 80% of their potential. In other words, a 12 volt battery is dead when it drops to 80% of 12 volts, or 9.6 volts.

I would suspect (I don't KNOW this, I just suspect) that as the 24 volt battery reaches 19.2 volts its power (the ability to drive its current) will diminish so much that even though it's 19.2 volts and all you want/need is 12 volts, I would expect it to be quite weak. I just don't think the power is going to be behind the voltage.

I would be interested to hear if this works. I'll be watching.