Hey Brian,
Good to see you made it here.
The numbers and calculations are a good place to start. I would like to hear what people are actually getting in practice.
I have motored for 7 hrs at about a 20 amp draw. At the time the prop I had gave me 3 knots at 20 amps. The prop I have now gives me 4 knots at 20 amps (with a clean bottom). That's 28 miles. I used one of my banks, I never tapped into the second bank. I may have run down the batteries pretty low, I did not have a monitor at the time but I still had power in the first bank at the end of that trip.
Regarding peukert effect I've heard that at the current levels we operate in the effect is minimal. In my view, the safety advantage of two separate banks outweighs any small capacity increase. I also like the ability to motor on one bank while charging the other.
So what kind of range are people actually getting?
Welcome Brian!
Mark
Santa Cruz
> Brian,
>
> Scattering the pack won't degrade your capacity by any significant amount, but it does add a considerable amount of large gauge cabling that adds cost and weight. The good news is that an Li pack with twice the rated capacity (and even more effective capacity) should fit right where your traction batteries are today.
>
> If you're thinking about using two similar but separate traction banks, take a look at the numbers that I published before. Looking at the T-105s, check out what happens when you install 16 batteries instead of 8. You get more than just double the duration/range, that extra capacity is basically "free" range and comes from reducing the Peukert Effect. FLA are affected the most, AGMs less and LiFePO4 very little.
>
> Using a DC/DC converter is pretty typical. I know someone that recently removed his house battery and mounted his DC/DC converter right next to his 12V panel. In the past, the cables from his house battery were large to handle the maximum amperage to the panel. If you're running a 400W converter (33A), the power leads can be much smaller running at 48V (less than 10A). He was able to remove 20 pounds of unneccessary copper from his boat. The converter will only shorten your range as much as you use various devices onboard. Increasing the efficiency of your lights and other electronics will only make everything work better/longer.
>
> The drawback to using only a converter for your 12V demand is that all of your electronics and lights will go completly dead any time that the main pack is switched off. An alternative is to add a small 12V motorcycle battery to even the line voltage and keep the station presets in your stereo. Given my earlier suggestion, you can see the advantage to putting the converter and small battery as close to the 12V panel as possible. If the converter is programmed to the correct output voltage, it will keep the battery charged without overcharging, any time that it is on.
>
> Fair winds,
> Eric
>
> --- In electricboats@yahoogroups.com, "drmsudo" <drmsudo@> wrote:
> >
> > Thanks for the calculations and insight. I would like to go with the LI tech for weight savings and space. Is there much degradation if you have the pack scattered around (a couple different spots I have in mind but are separated by 8 feet)? Also, I would like to put in a dc/dc converter to run the other "12v stuff" on board. That way I have one bank to monitor. I know it reduces the range, but I may just build it bigger to compensate. Currently I use two flooded batteries that have around 50 amp hours for house bank. I would just add that into my system. Other options are to keep my current system and make that the house bank but have the option to divert it to my motor to gain another 92ah. This would also give me the option to charge one while using the other. I know of another person that has their system set up like this. Again, thanks for the insight. I wish I knew about this group 3 years ago when I started this project.
> > Brian
>
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