# Foil Drive Assist, DIY

**URL:** https://foil.zone/t/foil-drive-assist-diy/12927
**Category:** Build, Repair & Mod
**Created:** [June 21, 2021, 3:51am UTC](https://foil.zone/t/foil-drive-assist-diy/12927 "2021-06-21T03:51:30Z")
**Posts on this page:** 1
**Showing post:** 1349

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### Author: ![Larsb](https://foil.zone/user_avatar/foil.zone/larsb/32/31021_2.png) [@Larsb](https://foil.zone/u/Larsb)
#### Post date: [February 3, 2024, 11:00am UTC](https://foil.zone/t/foil-drive-assist-diy/12927/1349 "2024-02-03T11:00:43Z")

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So, seems like some data went missing, to summarise what was there on the foil drive efficiency topic:

The current per cell in a pack with the same number of cells is the same regardless of how they are connected at a defined power level

12s3p at 3000w is 23A per cell  
9s4p at 3000w is 23A per cell  
This follows from the fact that each battery shares the load equally, same number of batteries, same load per battery.

If we add more batteries with one string of parallel batteries the relative difference is large since battery internal resistance goes down. With a moli p42 pack and a 12s3p vs 12s4p pack the internal resistance goes down from  
12x0.016/3=0.064ohm and 305W losses at 3kW  
to  
12x0.016/4=0.048ohm and 228W losses at 3kW  
This is a 3% gain in efficiency from the extra batteries

To compare with the resistance losses in the rest of the system:  
For a 10cm connection length of 8AWG wire the resistance is only 0.00041 ohm and at a 3kw the difference in current is  
3000/(8x3.6)=104A  
3000/(12x3.6)=69A

Resistance losses difference is 0.00041x(104^2-69^2)=2.4W This is negligible to the battery resistance losses - which are about 100 times larger.

On the esc side the losses are also small, at least with a good esc. An example is the APD 120f with 0.0011ohm resistance and a 7w difference in the esc resistance losses, about 40 times lower than the battery resistance losses.

On the motor drive side the losses from voltage and current is the same regardless of the DC voltage since the esc balances the output vs the load and throttle command, this is if it can do it with the current and voltage available. That’s a big if for drives that don’t reach foiling speeds😄

the difference that is worth the effort: propeller and motor drive efficiency. Getting up on foil is the most energy consuming part of the drive and limiting the time to get up is the key goal for a foil drive. With your system maxing at 3kW during starts you’ll consume half the energy if you get up twice as fast. I think this was the main point from @Jezza and the driver for the foildrive systems to go to higher voltage levels.

Of course all this is also highly affected by the size of your board, your foil and your skill level. As always, optimisation gets more important if you’re at the extremes.

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_[View the full topic](https://foil.zone/t/foil-drive-assist-diy/12927)._