T-Pain Is On A Boat: Re: [Electric Boats] Re: Battery charging time and overall efficiencies

Sunday, July 11, 2010

Re: [Electric Boats] Re: Battery charging time and overall efficiencies

"The NG3 does better, with 18A @ 115Vac (2070W) to 1500W output or 72% overall efficiency. While Dual Pro doesn't publish their current requirements, I believe that they operate much like the Zivan chargers in technology and therefore, efficiency."

Eric:

Interesting info. Thanks. Though I was led to believe that the Zivan NG-3 was a 220 volt charger one of the reasons I did not consider buying it. I have not seen a circuit diagram for my Dual Pro but, judging from how heavy it is I suspect it has four individual step down transformers in the unit where as the Zivan unit is fairly light in comparison. I need to get ambitious enough to measure the current on the legs of the Dual Pro after a significant discharge to see what it is actually putting out in the bulk charge mode. Though the Elcon 2000+ is rather impressive. If I were not so heavily invested in the Zivan and Dual Pro I certainly would have considered it. I think being able to get 23 amps out of it using the Honda 2000 would be real nice when motoring and provide a nice bump in speed for my electric propulsion system. But, then again I'm also happy with the 3 knots I get just using the Zivan at 16 amps. It's time to stop spending and concentrate on sailing.

Capt. Mike

http://biankablog.blogspot.com

--- On Sun, 7/11/10, Eric <ewdysar@yahoo.com> wrote:

From: Eric <ewdysar@yahoo.com>
Subject: [Electric Boats] Re: Battery charging time and overall efficiencies
To: electricboats@yahoogroups.com
Date: Sunday, July 11, 2010, 5:47 PM

While we're talking about overall efficiency from external power source to the motor controller, there are three major areas that should be considered; the ability of the charger to turn AC into DC (charger efficiency), the ability of the battery to store the provided DC (charging efficiency) and the ability of the batteries to deliver the stored energy to the motor controller (battery efficiency).

First, let's look at charger efficiency. The easiest way to evaluate a charger is to divide the watts coming out by the watts going in. Zivan chargers are common and according to their published specs operate at 85% efficiency, but the NG1 draws 12A @ 115VAC (1380W) and has a stated max output of 900W. This calculates to about 65% overall efficiency. The NG3 does better, with 18A @ 115Vac (2070W) to 1500W output or 72% overall efficiency. While Dual Pro doesn't publish their current requirements, I believe that they operate much like the Zivan chargers in technology and therefore, efficiency. Alternatively using a newer technology, PFC (power factor corrected) chargers like Delta-Q, Elcon, and Manzanita have overall efficiencies above 85%. My Elcon 2000+ will push 1400W from 14A @ 115VAC (1610W) or 87%.

Now, let's look at the batteries. Focusing only on the question of KWh in to KWh out, one of the obvious places to look is the charging voltage to discharge voltage. For this part of the discussion, I'm only talking about the current coming from the charger and the current going to the controller.

Assuming the amp hours are similar going in and going out, the difference is in the voltages. The max charging voltage for my 48V nominal Lithium battery pack is 60.8V, the resting voltage is 52.8 and the discharge voltage averages around 50V. In simplistic terms, the 9700Wh pushed into the batteries, stores at 8450Wh and will provide 8000Wh to the controller. This works out to about 80-85% charging efficiency for lithium batteries and flooded cells (FLA). If you consider AGMs with 14.4V in and 12.5V out, their charging efficiency is almost 87%.

So far, we've been assuming all amp hours in are available as amp hours out. There are other factors, the most apparent is the Peukert Effect, the energy lost due to the battery chemistry's inability to handle high amp loads. FLA suffer the most, AGM much less and Lithium very little. If we use an average load of 60A against a 200Ah bank, most FLA batteries will only deliver less than 60% of their rated capacity to 100% depth of discharge, AGM can deliver about 83% of their rated capacity and Lithium more than 96% of their rated capacity. Smaller packs with lower Ah ratings exaggerate these differences.

So the worst case scenario is FLA with an old charger or 70% (charger) times 80% (charging) times 60% (battery) where only 34% of the energy provided to the charger is available to the motor controller while under way. Just switching to a PFC charger will up that to 41% (85 x 80 x 60). Moving to AGM (85 x 87 x 83), they're operating around 61% total efficiency from outlet to motor controller. Finally, Lithium with a PFC charger (85 x 80 x 96) delivers just above 65% of the watts going into the charger to the controller during normal operation.

If you are running the charger from a generator while underway, you get to skip the charging and battery efficiency and focus entirely on the charger efficiency. This still ranges from 65% to 85%, so your results will depend on which charger you choose.

Fair winds,
Eric
Marina del Rey, CA

--- In electricboats@yahoogroups.com, "hardy71uk" <p0054107@...> wrote:
>
>
> Well I estimate on the back of an evelope as follows-> takes about 1.2kw hours per battery . so 4.8kwh total . if you had a 100% efficient charger that would take about 6 hours for an average input of 800watts. Say 8 to 10 hours for a reasonably efficient real charger. I'm guessing that the honda 1000 could probly provide 800watts continuous.
> Efficiency wise I think we are talking around 6.5KWH input for about 4KWH to the motor.
>
> Chris S
>
> --- In electricboats@yahoogroups.com, Aaron Williams <akenai@> wrote:
> >
> > If I had a 48 volt system with 4 12 volt 100 amp hour batteries how fast could they be charged. If I had a 10 kw generator how much would be wasted.
> > What I am wondering is if one of the Honda 1000 gen sets is more than adequate?
> >