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Old 11-06-2012, 08:07   #16
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Re: Electrical Musings

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Yes, 90% of the energy from the Sun is converted into heat.. but how much of that heat is converted into electrical energy?! I think I can come up with a near 100% conversion into heat but after that have to go to steam and turbines for the conversion to electrical energy....


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Old 11-06-2012, 08:48   #17
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Re: Electrical Musings

Jedi is right: use a DC ammeter to provide some reliable data so you can muse more efficiently :-)

A good AC/DC ammeter will tell you lots of things, not just how much current is being consumed from your house bank.

- You can measure the output of any onboard charging source: the Victron, the alternator, the solar panels, the Rutland, etc.

- You can measure the consumption of any onboard circuit, AC or DC.

Just be sure to record your measurements carefully, for later reference.

And, enjoy the freedom this will give you: no longer do you have to muse, "I wonder how much amperage this XXXXX is really putting out" :-)

Bill
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Old 11-06-2012, 10:04   #18
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Re: Electrical Musings

Dockhead-
Try Sandia National Laboratories: PV Modeling & Analysis and drill down. Sandia National Labs is a US government facility and they've got a lot of solid, confirmed, objective information on how solar panels perform. Including charts that can tell you "expect xx hours xx amps of performance" with compensation for time of year and latitude.
I expect there must be similar UK-based sources online.

Offhand, if you have a 24-volt 250W rated panel...yes, that should be good for 10A output and yes, in the southern UK you might see 4-5 hours of full power on a summer day and squeeze out more with an MPPT controller. You'd really need to run your latitude by one of the charts to see how optimistic that is or isn't, but the hard data IS out there. It just takes a bit of search querying to get it.
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Old 14-06-2012, 13:27   #19
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Re: Electrical Musings

Thanks to all of you for the very solid advice. I will definitely spend an afternoon with the DC clamp meter when I get back to the boat. Cheers, Dockhead
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Old 15-06-2012, 12:47   #20
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Re: Electrical Musings

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In just an hour and a half, say, I get what looks like a full charge – light load voltage up to 25.4 volts or so, which it holds for a couple of hours under this light load, then starts to slowly decline, reaching 24.3 volts
Are these readings taken at the battery terminals?
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Old 15-06-2012, 13:40   #21
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Re: Electrical Musings

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Are these readings taken at the battery terminals?
From my Victron battery monitor, which reads at the shunt, I believe.
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Old 16-06-2012, 03:54   #22
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Re: Electrical Musings

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I realize from these weeks that my 6.5kW generator (presently broken) is not really the best power source to support this kind of life on board. It is incredibly inefficient at charging my batteries using the 70 amp Victron charger. The acceptance rate falls to 10 amps or less (according to my battery monitor – probably it’s really getting double that) very quickly, and so it takes hours to accomplish what my main engine with its bigger alternator and more aggressive Adverc regulation does in an hour or so.
I would not blame the 6.5kw. It is the Victron that charge the batteries. If your main can charge the batteries in a shorter time than the Victron then it is the Victron that is not to the task.
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That WhisperGen Stirling engine gadget……
Alternatively, it will sound strange coming from the owner of a heavy-duty diesel genset, but a Honda E100i would be efficient – I would get no heat from it, but three or four hours should cover all my electrical power needs. My Victron charger/inverter can limit the power it takes from an AC power source, and has an appropriate setting for a 900 watt generator. I guess this would be the cheapest, simplest, fastest option.
The point is that 6.5kW of power can’t be used efficiently for battery charging. The battery acceptance rate is simply too low. And all of my AC power requirements – ALL of them, since I don’t have air conditioning – are perfectly fulfilled by my inverter. I just don’t need 6.5kW of AC power at one time, ever, unless I am washing clothes (and even that can be done from the inverter).
I doubt that the energy required (fuel consumption) to run your boat will wary much between the 3 generators quoted. What is sure it is that the smaller machines that are subjected to longer running hours will wear faster.
To generate Ac electricity, to rectify it, to store it in batteries in parallel, to invert it again, this is inefficient.
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And maybe that amount of solar would allow me to use my 6.5kW generator more efficiently – run the genset in the morning but only just as long as the batteries are taking a bulk charge, then shut it off and let the solar system do the absorption charge.
And the best way to achieve this when using solar is to have two banks one in use and the other being toped up.
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Old 16-06-2012, 04:56   #23
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Re: Electrical Musings

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And the best way to achieve this when using solar is to have two banks one in use and the other being toped up.
For most efficiency a single bank will be better. It is sometimes worth doing what you suggest to get batteries to 100% soc when there otherwise would not have been enough energy to do so. Batteries benefit from 100% soc occasionally and with some batteriesespecially AGM this is important.
Otherwise a single bank will be be better.
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Old 16-06-2012, 07:20   #24
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Re: Electrical Musings

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For most efficiency a single bank will be better. It is sometimes worth doing what you suggest to get batteries to 100% soc when there otherwise would not have been enough energy to do so. Batteries benefit from 100% soc occasionally and with some batteriesespecially AGM this is important.
Otherwise a single bank will be be better.
Exactly! Add to that, to use electricity as it's being generated is much more efficient than storing it in a battery and pulling it from that battery again. This means that you should run a genset at times that you can use as much of it's energy output as possible. Example: water maker, washer, A/C (drying & cooling the boat at the en of the day in the tropics), battery charger, water heater, coffee maker, etc. Many of these would need to come from the inverter oterwise!

cheers,
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Old 16-06-2012, 07:37   #25
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I am confused by the behavior of the Victron charger. It should output about 70 amps until the charging voltage reaches something like 28.8 volts (lead acid), then taper the current and hold the voltage for a period of time. I don't know the parameters on that charger, but with many you can specify the time of this absorption phase before it switches to float. The switch to float should occur when current reaches 8 to 10 amps on your battery bank. If you have a temperature sensor or sealed batteries the voltage will vary some.

To minimize generator run time, we have 2 inverter chargers and use the output of both to charge. Only one at a timefor inverting since they are different manufacturers. Some of the Victrons will parallel for both inverting and charging. As previously mentioned, this won't dramatically change the fuel required, but will save hours on the generator. And provide backup.

Solar is also good since it will extend the life of your batteries by reducing the cycle depth of discharge. Wish I had that....

Once you get the real current flow in and out sorted out. Then check your batteries to see that when you've used 1/2 of the bank capacity, about 200Ah the voltage should be around 24V. Variations here will give you a good idea of battery health.

Bob
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Old 16-06-2012, 07:39   #26
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Re: Electrical Musings

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Old 16-06-2012, 07:47   #27
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I thought about the FP DC generator too. We have friends on a Selene with one. They have 8 KW worth of inverter power and a huge battery bank. The FP kicks in automatically to keep the batteries charged. Virtually silent inside and outside the boat.

But....their service record has not been stellar. Does anyone have one with lots of hours and no problems? if so what are the secrets?

Bob
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Old 16-06-2012, 08:02   #28
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Re: Electrical Musings

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I thought about the FP DC generator too. We have friends on a Selene with one. They have 8 KW worth of inverter power and a huge battery bank. The FP kicks in automatically to keep the batteries charged. Virtually silent inside and outside the boat.

But....their service record has not been stellar. Does anyone have one with lots of hours and no problems? if so what are the secrets?

Bob
I got lots of hours on one... that is, hours of paid repairs and in the end removal, which also had to be paid for. They tossed it into the bin, that's how much it was worth to them...

When you buy a big alternator and store it in your bilge, it is much more cost effective and about the same energy supply

Replaced with Northern Lights and never had to hire a mechanic again since 2003...

cheers,
Nick.
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Old 16-06-2012, 08:43   #29
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Re: Electrical Musings

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For most efficiency a single bank will be better.
If a single bank consists of two or more battery in parallel then this configuration will be one of the less efficient. It is known that to charge a battery more energy must be provided to the battery than the battery will return. Up to 20% more energy as been quoted. If for example a 14 amps current was drawn from a bank of 3 batteries it will be pure luck if the load was equally shared. It is possible to observe for similar batteries a discharge ratio of 8A for the closest battery and 2A for the furthest. When the discharge current is interrupted the batteries will equalize and in doing so up to 20% of the energy transferred will be wasted. This wastage will also occur each time that the chemistry of each battery differs. In a 2 battery bank this wastage can be minimized by the use of a blocking diode. It is also interesting to note that when some one start to connect two battery in parallel they, most of the time ad more and it can also be said that when the configuration reach 5 battery, the 5th battery do no more than compensate for the wastage. Unless each battery is equipped with a way of monitoring the circulating current this wastage will remain unnoticed. This may explain the serious discrepancy that occurs between the energy supplied to the bank and the energy returned from the bank.
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Old 16-06-2012, 09:13   #30
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Re: Electrical Musings

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If a single bank consists of two or more battery in parallel then this configuration will be one of the less efficient. It is known that to charge a battery more energy must be provided to the battery than the battery will return. Up to 20% more energy as been quoted. If for example a 14 amps current was drawn from a bank of 3 batteries it will be pure luck if the load was equally shared. It is possible to observe for similar batteries a discharge ratio of 8A for the closest battery and 2A for the furthest. When the discharge current is interrupted the batteries will equalize and in doing so up to 20% of the energy transferred will be wasted. This wastage will also occur each time that the chemistry of each battery differs. In a 2 battery bank this wastage can be minimized by the use of a blocking diode. It is also interesting to note that when some one start to connect two battery in parallel they, most of the time ad more and it can also be said that when the configuration reach 5 battery, the 5th battery do no more than compensate for the wastage. Unless each battery is equipped with a way of monitoring the circulating current this wastage will remain unnoticed. This may explain the serious discrepancy that occurs between the energy supplied to the bank and the energy returned from the bank.
I am not sure I am following your argument.
If the batteries are correctly wired the resistance to all the batteries in the bank will be equal so the discharge will be even.
A larger bank charges more efficiently ( efficiency goes down with higher charging voltages). It also discharges more efficiently due to Pukets equation.
Discharging one battery bank while charging another brings about the charging efficiencies you are quoting.
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