# Need help with resistor for charging a capacitor safely

#### shoolster

Joined Sep 30, 2015
14

I verified the stock alternator puts out 160 amps and usually runs around 13.85 volts at the accessory lugs on my dual battery setup

Capacitor
http://www.ebay.com/itm/231647617424?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT

Calculator
http://mustcalculate.com/electronics/capacitorchargeanddischarge.php?vfrom=2&vto=14&vs=14&c=433&r=.5&time=900

Resistor
http://www.mouser.com/Passive-Components/Resistors/Wirewound-Resistors/Wirewound-Resistors-Chassis-Mount/_/N-7fx9g?P=1z0wn8jZ1z0x6wc

#### shoolster

Joined Sep 30, 2015
14
Excellent I was hoping it would be something simple. So in parallel it will divide the ohms by the number of resistors and multiply the watts? Thanks for the help.

Joined Nov 5, 2010
212
Excellent I was hoping it would be something simple. So in parallel it will divide the ohms by the number of resistors and multiply the watts? Thanks for the help.
The wattage of the four parallel resistors is additive to get the total wattage. You want extra total wattage so they don't get too hot during their high-current phase.

The resistance in parallel in general is 1/Rtotal = 1/R1 + 1/R2 + 1/R3 + 1/R4. But when they're all the same resistance, the resistance just averages.

Joined Nov 5, 2010
212
Capacitors like this have so much energy they can be dangerous. What are you doing with this?

#### shoolster

Joined Sep 30, 2015
14
Capacitors like this have so much energy they can be dangerous. What are you doing with this?
It helps to power 4 dash cams in my Jeep so I stop killing off very expensive Odyssey batteries. It started as a simple plan to have the cameras for security and has turned into a more complex affair. That is of course why I came on to ask for the assistance, the resistor was the only part I wasn't sure of and I want it all done as safely as possible.

Thanks for the help.

Joined Nov 5, 2010
212
You should post an overall schematic of your main battery/accessory battery/capacitor charge/camera discharge circuitry.

#### Roderick Young

Joined Feb 22, 2015
408
Try looking up the BCAP2000 or BCAP3000 on mouser.com . You'll see a data sheet there. It's showing the maximum current of the BCAP2000 as 1500 amps, so I don't think you can hurt the capacitor with the alternator. What you do need to worry about is putting too great a load on the alternator, and I guess that's what your calculation did? You might also consider whether you can just use some thinner wire like #14 stranded, to limit current during charging. Just do the math to figure out wire heating and proper insulation.

A cheaper choice, with longer runtime, would be simply to use a sealed lead-acid battery.

Also note that the product in your link uses passive resistors to balance voltages across the capacitors - not very good when a fast charge rate is involved.

#### shoolster

Joined Sep 30, 2015
14
You should post an overall schematic of your main battery/accessory battery/capacitor charge/camera discharge circuitry.
I will once I get it fully (at least mostly) installed over the next few days

#### shoolster

Joined Sep 30, 2015
14
Try looking up the BCAP2000 or BCAP3000 on mouser.com . You'll see a data sheet there. It's showing the maximum current of the BCAP2000 as 1500 amps, so I don't think you can hurt the capacitor with the alternator. What you do need to worry about is putting too great a load on the alternator, and I guess that's what your calculation did? You might also consider whether you can just use some thinner wire like #14 stranded, to limit current during charging. Just do the math to figure out wire heating and proper insulation.

A cheaper choice, with longer runtime, would be simply to use a sealed lead-acid battery.

Also note that the product in your link uses passive resistors to balance voltages across the capacitors - not very good when a fast charge rate is involved.
Correct on the calculation I wanted something that would charge reasonably fast without a massive power draw. What would you consider to be fast-charge? With the .5 ohms from the roughly 4.8 low end it should average it shows about 15 minutes to roughly 14 volts. I ended up buying the linked resistors (4) below from mouser.com this morning to follow k7elp60's advice

http://www.mouser.com/Search/ProductDetail.aspx?R=HS150_2R_Fvirtualkey11260000virtualkey284-HS150-2.0F

I am also running a leg off the 8 gauge to power the relays to make the Lukas LK-350 handle 4 cameras rather than only 1 so it would only make it more complicated (at least beyond my abilities) to calculate a proper wire gauge.

It was likely cheaper and easier to do the battery but I was interested in playing with a capacitor and this seemed like a good project to try it on. Also I have two expensive batteries already and this only weighs 9 lbs. With the 2 batteries connected to certain voltage levels that will disconnect themselves (see first post) the capacitor will not be the only source of power it is supplemental. With the 40 amp 400 volt diode it mostly will power them for the short times during the day the vehicle is off instead of constantly draining my two batteries. I have a huge winch and tons of lights, etc... on the Jeep and I try very hard to keep the batteries healthy for the emergency off-road situation and since installing the cameras I have already killed off two accessory batteries and a main battery (under warranty) and I would hate for something to happen while off-roading. Thanks

#### shoolster

Joined Sep 30, 2015
14
You should post an overall schematic of your main battery/accessory battery/capacitor charge/camera discharge circuitry.
I said installed, I meant to say figured out. I just sourced all the parts this morning and once I have them in hand and laid out I can make a diagram better.

#### ScottWang

Joined Aug 23, 2012
6,779
When you trying to using the super capacitor to charge, you should know about the resistor of average voltage, you can reading quickly for all page and back to see the section of Series/Parallel Combination Of Ultracapacitors?

Ultracapacitor & Supercapacitor Frequently Asked Questions.

#### shoolster

Joined Sep 30, 2015
14
When you trying to using the super capacitor to charge, you should know about the resistor of average voltage, you can reading quickly for all page and back to see the section of Series/Parallel Combination Of Ultracapacitors?

Ultracapacitor & Supercapacitor Frequently Asked Questions.
That was one of the first articles I read when deciding to learn more about these capacitors. Specifically these points make me think this is the correct setup for my application, mainly the unlimited discharge cycles:

• Ultracapacitor Functions
• Secure power
• Provides reliable interim power, even if the primary source fails or fluctuates
• Energy storage
• Stores energy from low power sources, enabling support for high power loads
• Pulse power
• Supplies peak power to the load while drawing average power from the source
• User Benefits
• Reduces the size & weight of the battery / power source required
• Improves run-time & battery life, particularly at cold temperatures
• Enables more power-hungry features, being used more often
• Can remove the need for a battery & harvest energy from clean sources
• Protects against accidental power loss or fluctuations/interruptions
• Doesn’t need to be replaced like batteries (unlimited discharge cycles)
• Environmentally friendly & safe
I guess you are saying it is likely better to have gotten a setup with an active balancing circuit rather than the passive setup I got considering the high level of cycling I will be exposing it to. Will it be a huge problem or is that simply "better" but the passive balancing will still work just not prefered? As I said I am only just learning and like anybody I won't get everything right the first time but that's how we learn, and that's why I came to ask the pros. If it was an easy project I wouldn't be interested. Thanks

#### ScottWang

Joined Aug 23, 2012
6,779
If something you never play with then you need to start from the small project is better as buy some 1uF/2.7V to try the characteristics, spend less money to creating the conception, that is better than just reading and reading.

Some problem may not happen immediately, but it will happen some day, so you have to follow what the guiding or datasheet mentioned, if you don't in parallel the resistor, the capacitors will still working just fine, but when day by day, soon or later it will be happened suddenly, if you thinking about the spring then you will see, specially when your project is a big current, it means that safety and a lot of money.

#### blocco a spirale

Joined Jun 18, 2008
1,535
I don't believe that any of this is necessary.

Are you just trying to run the cameras when the engine is off without draining the main battery?
How long do you expect the capacitor to run 4x dashcams for?

I said installed, I meant to say figured out. I just sourced all the parts this morning and once I have them in hand and laid out I can make a diagram better.
Normal practice is to design first then source components.

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#### shoolster

Joined Sep 30, 2015
14
I don't believe that any of this is necessary.

Are you just trying to run the cameras when the engine is off without draining the main battery?
How long do you expect the capacitor to run 4x dashcams for?

Normal practice is to design first then source components.
Necessary is a subjective term. Nobody has yet presented a reason why it won't work only various (helpful) critiques of the approach, for example the cameras themselves are powered by internal capacitors to allow a recording to finish if power is cut. It certainly doesn't fall into the realm of un-necessary, and if people only built things others deemed to be necessary more than half the items that exist in this world would not have been built.

I'm definitely not taking them out since they feed into my screen on my dash and I can cycle through the rear 3 cameras using my steering wheel controls onto my display. They also give me full HD recordings of my off-road activities from all 4 sides. I just want to stop replacing my batteries constantly because the drain.

Yes the plan is to have the capacitor to supplement the two batteries not be the sole source of power. On my bench it held out for about 3-4 hours from only 13 volts on it's own but when combined with the batteries I am hoping for about 24 hours total runtime. The cameras drop into a low power parking mode after 10 minutes of inactivity drawing only 1.5 watts each. I linked the manual below. Pg 32 shows they only draw 2 watts each on 5 volts at 3 amps prior to the low power mode.

https://www.cyberphoto.se/autocam/finevu_manual_eng.pdf

You're right about the design, I do have it in my head and could/ will go ahead and scratch it out on paper. Most of the components have been installed for a few years now (except the LK-350 it is a few weeks old), it's only the capacitor, the diode, and the resistors that need to be added.

It uses this 200 Amp Cole-Hersey Isolator
http://www.colehersee.com/home/item/cat/211/48530/

I have these batteries as recommended by Genesis for maximum capacity
http://www.amazon.com/gp/product/B00249CSS2?psc=1&redirect=true&ref_=oh_aui_search_detailpage

This is the Lukas LK-350 manual which I cut up used some relays to up the output power to handle the 4 cameras. I have it set to cut off at 12.4 volts
http://www.lukashd.com/gnuboard4/bbs/board.php?bo_table=eng_automanual&wr_id=6

Everything above is installed and works as planned.

I ordered this diode yesterday
http://www.amazon.com/gp/product/B0056RH3P2?psc=1&redirect=true&ref_=oh_aui_detailpage_o03_s00

I linked to the new resistors in a previous post. I am building a custom rack from aluminum angle to hold the capacitor and the resistors with be bolted to it (and thermal pasted) for additional heatsink capabilities. It is on my dedicated 8 gauge cable with a 40 amp fuse under the hood.

If somebody has a specific reason my plan is doomed to fail for a reason other than operator error I am all ears but I haven't heard it yet. Keep in mind this is not some electrical engineer building a shiny thing for a corporate client- I'm just a smart guy wanting to build something new and I would like everyone's constructive criticism to make it work rather than a barrage of negativity. Nobody is being negative yet but everybody knows how these posts devolve into that quickly once someone expresses the slightest bit of dissension, and that is the number one reason people like myself avoid posting. Thanks everybody for the help in getting this done correctly.

#### blocco a spirale

Joined Jun 18, 2008
1,535
"Necessary" is hardly subjective and engineering is not about finding solutions at any cost. I could enter my house through the chimney but no one would argue that it's "necessary" to do so when I can just walk through the front door.

When you say you want constructive criticism you actually mean that you don't want anyone to tell you that there is a better or easier way.

To cut through the fog; How long will the super-capacitor on its own run the 4 cameras for? I ask this because this is all the additional running time the capacitor will give you. If it's 3-4 hours then how much extra battery capacity would be required to achieve this extended run time and how does that compare with the cost and complexity of the capacitor solution?

If the cameras were over-discharging the battery then the logical solution is to fit a low-voltage cut-off to disconnect the cameras and prevent this happening and if you need a longer run time, fit a larger battery.

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#### shoolster

Joined Sep 30, 2015
14
"Necessary" is hardly subjective and engineering is not about finding solutions at any cost. When you say you want constructive criticism you actually mean that you don't want anyone to tell you that there is a better or easier way.

To cut through the fog; How long will the super-capacitor on its own run the 4 cameras for? I ask this because this is all the additional running time the capacitor will give you.

If the cameras were over-discharging the battery then the logical solution is to fit a low-voltage cut-off to disconnect the cameras and prevent this happening and if you need a longer run time, fit a larger battery.
I absolutely want someone to tell me if there is a better solution, I am fully open to suggestions. I am currently looking into the alternative Roderick Young mentioned with a small battery. I have not been able to find anything else along that route that appeared to have more available power than the capacitor that would not need to replaced at some point. My statement was qualified by the fact that nobody yet had proposed why the idea would not work, but if it won't then please tell me and I will go another route. I don't want to be told I am right, and I promise if someone has a viable alternative I will be the first to admit it and make the change. Constructive criticism is only in play when someone is helping to improve the idea. With that said...

The Lukas-LK350 is that low voltage cut off, I installed that recently for the reason you mentioned. My thought with the capacitor was for example if I go somewhere and the vehicle is off for short periods the capacitor will power the cameras without even touching the batteries. Overnight it would go through the cycle of disconnecting batteries, etc... and will still die off eventually. As I noted on my bench it was charged to only 13 volts and managed roughly 3-4 hours running the cameras (I wasn't there when it died to know for sure).

I could not find a larger capacity battery that fits inside the dual battery setup or I would go that route. Genesis told me those are the largest capacity batteries that fit.

I am 100% on board with returning \$400 worth of stuff for a cheaper/ better solution. Am I correct that basically any reasonably sized battery alternative will fail eventually and not supply a substantial amount more power? In my opinion it appeared when comparing the available power from fully charged down to 12.4 volts (where the LK-350 would kick in to protect the new battery) on an additional battery vs the amount available from 13.85 volts down to 5 on the capacitor it was not an advantage. Obviously I might be wrong but that's what it looked like to me.

My thinking is I will have the capacitor power the cameras until the voltage falls to the level of the connected batteries. The batteries will then contribute until 12.7 volts, after 1 minute there the isolator will disconnect the main battery. Then the still connected accessory battery will stay connected down to 12.4 volts and get disconnected by the LK-350. At that point the capacitor will continue on it's own down to 5 volts and everything will shut down. In that scenario it did not appear a small battery would add more energy as it would also get cut off at 12.4 volts. Space is a premium in the cargo area of a Jeep so a full size battery is not an option and weighs considerably more than this 9lb capacitor. If I am not right and a small battery is an advantage I will immediately return everything linked above and make a new post regarding you guys helping me with a better solution than I came up with. Thanks

#### blocco a spirale

Joined Jun 18, 2008
1,535
Super-capacitors have specific applications where a battery would be completely unsuitable but this is not one of them.

If you can't increase the capacity of the main battery; work out, in Ah, how much energy the cameras need to run for however long you need and find a battery that will supply this. Lithium polymer batteries have very large energy density for their size and weight and, compared to a capacitor, they have a nearly flat discharge curve so more of that energy can be used.

Simply run the cameras on the main battery and then switch to a dedicated camera battery when the voltage reaches its lower limit.

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#### shoolster

Joined Sep 30, 2015
14
I am working on the math now but I had a question.

From looking at the Lithium polymer batteries it seems the charging has to be done extremely specifically, how would that best be done with my setup?

Separately what about something like this small battery which could just be dropped into my existing charging system without any equipment except a diode to not send the charge back to the front 2 batteries. I am open to the change if it's a better solution since these are small and light I can just make the frame differently. Roderick Young mentioned a sealed lead acid battery and you mentioned the lithium polymer. This one seems not as good as the lithium polymer but easier for me to charge but looks like a little more powerful than a lead acid battery for it's size.
http://www.batterytender.com/Batteries/480-CCA-Lithium-Engine-Start-Battery.html

Thanks again