3s vs 4s LiPo for FF

[john from md]

Hell, you'll get a full day out of 6.3AH! I haven't met anyone that can do that more than once in a yak.

Regards,

John

[HereFishyFishy]

i just Googled the humminbird 718 and downloaded the pdf of the operators manual. In the back, there is a spec section that says "Power requirement - 10-20V" . It also indicates a current draw of 300ma and I assume the current draw is for a lead acid battery at 12 V. Based on that doc, you could use either the 3 cell or 4 cell series pack. The FF will probably draw proportionally more current at 11V ( 327ma) then at 14.5 V (248 ma) and the the battery lifetime will vary accordingly. Besides the power density, another really nice thing about these packs is that the self discharge while sitting on the shelf is almost negligible.

[john from md]

"Besides the power density, another really nice thing about these packs is that the self discharge while sitting on the shelf is almost negligible. "

Another good feature is that they don't like to be kept fully charged. Considering how many of us forget to charge our lead acids this is a real blessing.

John

[tufnik]

i just Googled the humminbird 718 and downloaded the pdf of the operators manual. In the back, there is a spec section that says "Power requirement - 10-20V" . It also indicates a current draw of 300ma and I assume the current draw is for a lead acid battery at 12 V. Based on that doc, you could use either the 3 cell or 4 cell series pack. The FF will probably draw proportionally more current at 11V ( 327ma) then at 14.5 V (248 ma) and the the battery lifetime will vary accordingly. Besides the power density, another really nice thing about these packs is that the self discharge while sitting on the shelf is almost negligible.

Thanks for checking. I'm no EE, but I thought the higher voltage will result in higher amp draw. V = iR, where R = constant. At 4s, draw should be higher than at 3s. Am I missing something?

Since I have the cells, I may build the pack to 8400 mah. Just in case I end up buying a color FF with all the fancy pancy.

Yeah, little discharge. I had the cells sitting on the shelf for 5-6 years. Of the 25 cells, 19 cells show voltages close to 4 v. The other 6 cells are questionable; they range from zero to over 2 volts.

[HereFishyFishy]

For most electronics, the correct assumption is that the electronic load will use constant power. Power = Volts * Current. So if the V goes up, the current goes down. This is an assumption, but I did stay in a Holiday Inn Express in the last year or so.

[smb]

Draw is based on the load (fishfinder) and does not increase/decrease based on battery type.

Current and voltage are proportional. Current is inversely proportional to resistance, so for example in a short circuit resistance is reduced and current goes up until the short opens.

This may help:

http://www.ndt-ed.org/EducationResou...urrentflow.htm

[tufnik]

Ahh...yes, fair assumption, Fishy. Although power actually varies based on sensitivity setting, screen brightness, beep frequency, etc. I'd say you slept well at the Inn.

[tufnik]

Draw is based on the load (fishfinder) and does not increase/decrease based on battery type.

Current and voltage are proportional. Current is inversely proportional to resistance, so for example in a short circuit resistance is reduced and current goes up until the short opens.

This may help:

http://www.ndt-ed.org/EducationResou...urrentflow.htm

That's true. That's why I thought draw goes up when voltage goes up (battery voltage from 3s to 4s). Fishy is saying for the constant power assumption, draw goes down when voltage increases.

[chex]

Hey tufnik, have you been using the LiPo battery? Is it working out?

[HawkGT]

I looked into the question of how much longer a higher voltage pack would last and decided that the critical question was how the fishfinder was constructed. If it has a linear power regulator chip in it, which seems like a reasonable assumption, then the extra voltage would be dissipated as heat. If you really wanted to max the power efficiency, you would add a high efficiency dc to dc drop down power converter set to 11 volts. What do you think?


Sent from my iPad using Tapatalk

[tufnik]

Hey tufnik, have you been using the LiPo battery? Is it working out?

Built a 4S3P lipo pack at 6300 mah. You can see the individual cells I used. Used 12 cells to provide 14.8 volts. Pack weighs 25 oz. I also added a balancing tap.

I haven't used it yet. I couldn't find a waterproof case, so the pack sat on the shelf. Since you reminded me, and now I have a new Outback, will install the new pack.

[tufnik]

I looked into the question of how much longer a higher voltage pack would last and decided that the critical question was how the fishfinder was constructed. If it has a linear power regulator chip in it, which seems like a reasonable assumption, then the extra voltage would be dissipated as heat. If you really wanted to max the power efficiency, you would add a high efficiency dc to dc drop down power converter set to 11 volts. What do you think?


Sent from my iPad using Tapatalk

From my RC experience, the higher voltage may last longer. I think you're right about dissipation. Don't think I want mess around with a converter, and I really don't need that much more energy because I already have 6.3 amp-hr. The big thing I like is that as the voltage drops, it would not hit the cut-off voltage sooner than a lower voltage pack.