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Old 02-02-2017, 11:15 PM   #1
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capacitor batteries

Well the time has come for me to seriously think about battery banks and all that. I have been watching the youtube and came across this fella using super capacitors in place of batteries. I kinda like it because I figure I can fill up my battery box with enough capacitors to run the engine needs AND fill my electrical requirements as well. There is no real limit on the demand I can place on them, they never freeze or wear out...but they don't have as much stamina....unless you have a ton of them...which I'm kinda thinking about. You can also use a hand crank generator to recharge if you accidentally leave the lights on...takes about 10 minutes. What do you think?
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Old 02-03-2017, 12:59 AM   #2
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I am guessing you have watched laserhackers Youtube video here - - he is a regular for me to watch!

I would not recommend this for something mission critical like your startup systems. A bus takes a ton of AMPs for both starting and keeping the bus running. If your alternator failed or started to fail, you would have an immediate dead battery.

Unfortunately, to be able to use these capacitors to power anything other than lights, you would need a whole lot of them. In the video here - he shows what a large bank looks like and how it can be used with heavy loads along side a solar panel, but the bank you see in the video with the inverter costs more than $1400 to build!

Without the solar power, you might get a few min of use at 400W before the capacitors discharge below the point that the inverter will work. With a solar charge, you could probably get more time, but not reliably I dont think. If you watch toward the end, he talks about why this is not a viable solution yet due to not being able to draw all of the power from each capacitor.

I do however see a huge use for this as an initial load reduction tool for your batteries. Things like fridges, air conditioners and pumps can put a large drain on batteries on initial startup. A capacitor bank would help protect the batteries from sharp pulls of energy, which particularly for lithium iron phosphate, is important. They like long slow even draw of power to be most efficient. When sharp increases in power requirements happen, it can cause the battery to operate less efficiently and in some cases fail.
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Old 02-03-2017, 02:29 AM   #3
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I like the idea, but I'm not sure the problem with air conditioners and fridges is the batteries - it's the inverter. The starting draw is more then the inverter can put out.
The solution is to buy a bigger inverter - but those suckers are expensive, and I'm not sure if the larger ones are as efficient as the smaller ones.

Adding power to the battery side isn't going to help the output side of the inverter. You have plenty of power - but not in the format that you need it in.
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Old 02-03-2017, 02:50 AM   #4
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Quote:
Originally Posted by Mark_In_MA View Post
I like the idea, but I'm not sure the problem with air conditioners and fridges is the batteries - it's the inverter. The starting draw is more then the inverter can put out.
The solution is to buy a bigger inverter - but those suckers are expensive, and I'm not sure if the larger ones are as efficient as the smaller ones.

Adding power to the battery side isn't going to help the output side of the inverter. You have plenty of power - but not in the format that you need it in.
In our bus, everything will be powered by 12v/solar or propane - Fridge, washer, stove, heat, and cooling. We will have inverted power on board but not for critical systems, more for things like electronics and tools. These will most commonly run off of a small ultra quiet low wattage genny (~2000w).

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Old 02-03-2017, 09:13 AM   #5
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Quote:
Originally Posted by Mark_In_MA View Post
I like the idea, but I'm not sure the problem with air conditioners and fridges is the batteries - it's the inverter. The starting draw is more then the inverter can put out.
The solution is to buy a bigger inverter - but those suckers are expensive, and I'm not sure if the larger ones are as efficient as the smaller ones.

Adding power to the battery side isn't going to help the output side of the inverter. You have plenty of power - but not in the format that you need it in.
Anything with a decent size electric motor will have a startup current draw significantly higher than its running current draw. Like Mark said, you need to size your inverter to accommodate this.

That said.... I have seen MANY properly sized inverter installs that were hobbled by battery/cabling issues that prevented them from supporting high startup loads. If you cannot provide the inverter with the input power it requires you will certainly fail to see the output you seek.

Personally, I have done it myself. After much research I purchased a 2000 watt PWS inverter to run a refrigerator. The inverter shipped with 6' long #4 DC cables. When installed with these cables the inverter ran fine. It supported all of the loads it was asked to EXCEPT the refrigerator. While testing I plugged 4 x 500 watt halogen work lights. Kill-a-watt told me that I was actually consuming 2250 watts. No problem.... Except that it still won't start the compressor on the refrigerator.

I replaced the 6' long #4 DC cables with 2' long 1/0 cables. Problem solved.

The voltage drop across the DC supply cables was enough to starve the inverter under the startup load from the refrigerator compressor.

Battery capacity and proper cabling are (IMHO) equally important to inverter size. A properly engineered "system" is what we are after.
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Old 02-03-2017, 09:51 AM   #6
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Good basic info. So many folks size based on running draw without taking "start up" into account which can double the rated draw. That combined with undersized wires can render a system useless even after spending a bunch of money.
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