Author Topic: common design flaws  (Read 5169 times)

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spacecase0

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common design flaws
« on: August 07, 2015, 12:29:38 PM »
lets talk about common design flaws, please share any you know of

here is one that I see many people make all the time, (walking you through the point of view of the not correct set up system)
when setting up solar power, people often fuse the battery wires, usually something in the 15 to 30A range
and while this seems like a good idea, let us think about what happens if that fuse ever blows,
the moment the short clears,
the voltage drops as there is no longer a battery in the system and the capacitor in your radio is likely the only thing powering everything,
then your charge controller connects off the approximately 22V open circuit voltage of the solar to now only your radio,
this will charge the filter capacitors in the DC input of your radio very fast
the charge controller will try to shut off again somewhere at 14.2V,
but most charge controllers take somewhere in the range of  0.2 seconds to turn off
that is running a huge risk of breaking your radio from over voltage
let's say you put an unfused 4700mF cap. on the DC buss, (I tested this for fun)
my setup is a 100 W panel and a sunforce 7A charge controller (pretty standard 12V system)
this limits my peak voltage to 16.96V when the battery is unplugged and there is no load on the system, with a 1/2 amp load on my system I get a peak voltage of 15.39V
the book for my ft-857 says 13.8V +/- 15%, so that is a peak of 15.87V, my VX-7R says 16V max (I am not testing what they can actually take)
so if my FT-857 is turned on and the battery fuze breaks, it should be fine, but entirely unsure what max voltage the radio can take when turned off.(not testing that either)
also tried a 3.5F super cap., and the peak voltage is 14.28V (so that would work fine)
the real solution:
the design flaw is connecting your solar charge controller to your DC buss with everything else
should be set up to connect the charge controller to the battery with a fuse between the 2, and then putting a fuse going out from the battery to the rest of your DC bus, this means you have 2 connections at your battery and not just one.
maybe a schematic would have been easier to show all of this...

anyone else have a design flaw they see all the time ?

W.Lynn

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Re: common design flaws
« Reply #1 on: August 08, 2015, 10:55:46 PM »
I like your description, but a schematic (and maybe photos,) would be very nice.

Tevin

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Re: common design flaws
« Reply #2 on: August 09, 2015, 04:30:59 AM »
lets talk about common design flaws, please share any you know of

[snip]

anyone else have a design flaw they see all the time ?

I follow what you are saying but I'm not sure how much it matters. A lot of this depends on what kind of controller you have.

Most charge controllers, the larger/better ones anyway, have a low/no battery voltage shut off. These devices will not let you place a load directly on the output with no battery. Even if it did, it would not allow more voltage than what the output is rated for. For example, my Morningstar Tri-Star 45 is set to a maximum of 14.30 volts out. No matter how high the input goes, the other side of that controller is never going to let more than 14.3 volts though.

If the battery fuse blows, the controller senses a no battery condition and shuts off. The entire system is depowered and the situation you describe cannot occur.

I also have a small/cheap 10 amp PWM controller and have never tried seeing what it does with no battery on the output.

To address your situation, the Sunforce 7 amp controller is rated for 14.20 volts out. There is some wiggle room on that, but the top end of that controller should always be very close to 14.20 volts. If you are getting 15.39 volts with a 0.50 amp draw, that is well beyond acceptable "wiggle room". Something is wrong. From what you describe, your controller is not really controlling anything.

To salvage your controller, maybe you can add one of the DC-DC converters you mentioned in another topic to get the voltage down to where it should be. You won't have the cutoff voltage anymore but you can compensate by splitting the difference and set the output to, oh, 13.7 volts would be a good middle spot. It's enough to power your equipment but not so much that your battery will fry. 

Morningstar used to make a really nice basic 7 amp controller and also a 10 amp. I have the 10 and its perfect for my little side projects and experiments. I think I paid about $40.00 for it a few years ago. Unfortunately, it looks like Morningstar discontinued both products and now offer only a 25 amp version for $84. Not exactly a budget model, but at least it has room for expansion.





spacecase0

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Re: common design flaws
« Reply #3 on: August 09, 2015, 01:39:17 PM »
the sunforce charge controller is not broken at all,
it is just an electric on off switch that connects the solar to the batteries when the battery is low and disconnects when the battery is full, if you have no battery connected the output will go to almost the solar panel voltage (22V)
when I got mine the higher current versions were relay driven, so they were an actual switch inside.
if you have a battery connected it has no issues working in the proper voltage range

I know the fancy charge controllers are out there now, ( by the way, I have never seen anyone buy one where I live unless directed to do so)
I got most of mine before the fancy ones were really available ( the shunt controllers were out there long ago as well, but they just make to much heat for me to get one), and I can't really afford any of them now.
I do use my DC to DC switching supplies as charge controllers as well, and they clearly don't have the high voltage issue and can run the radio with no battery at all, but they do have some RFI, so when running the HF radio I tend not to use them as often.
(by the way, the MPPT regulators I have played with are even worse with RFI as they seem to have not bothered to filter the output hardly at all )

in case you are wondering how I get to play with hardware that I clearly don't own,
I help others set up systems, usually after they have failed in some way, or think they have failed,
so I setup whatever they have bought and get to see how well it works.
people around here don't usually have much money, so they are not typically getting high end anything.

Tevin

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Re: common design flaws
« Reply #4 on: August 10, 2015, 09:07:06 AM »
spacacsse0, I'm not sure what to tell ya....

If your controller is truly not broken and is putting out 22 volts when it should never go above 14.2, then you have a "controller" with a design flaw so deep that it makes the device completely unuseable. I'll go even further than that and say it should be recalled because iit is a very serious safety hazard. My advice is to remove iit from service immediately and go find something else.

You may not like the fancy new stuff, but at least the fancy new stuff actually works. By the way, there are reasonably priced PWM controllers out there that will work properly and stay within their specified voltages.

I've been using an MPPT controller for years with no issues with voltage or RFI. RFI is a fixable problem. Design flaws such as the one you describe are not.

If you insist on keeping that controller, then I strongly suggest you place a normally-open relay on the positive lead coming in from the solar panel, and connect the relay contact control wire to any point on the positive battery lead that is protected by the battery fuse. If the fuse blows, the relay will open and cut the solar feed to your controller, thereby halting the runaway voltage condition.

I've seen your other posts and I know you as a very resourceful & skilled tech. You can easily do this.




spacecase0

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Re: common design flaws
« Reply #5 on: August 10, 2015, 11:34:32 AM »
the PWM controllers have the same issue I am talking about,
with no battery connected the voltage goes to high
give me some time to put a few schematics together to show what I am trying to say

and the solution to using them is much simpler than a relay setup,
you just have 2 fused connections on the battery, one to the charge controller and one to your loads.
I will make up schematics and post them in the next few days

jdh

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Re: common design flaws
« Reply #6 on: August 13, 2015, 06:39:27 PM »
Since my charge controller and batteries are both on the same side of the battery protection/fire prevention fuse (60 amp in my case) and the radio is on the other side of the fuse how will the charge controller directly power the radio when the fuse blows?  The charge controller is there to charge the batteries.  The fuse is connected directly to the output of the battery bank with 2" of wire from the terminal to the fuse.  It is there to disconnect the batteries from a hard short that would cause the wiring or the batteries themselves to become hot enough to become a source of ignition or draw high enough current to warp the plates causing the batteries to be ruined.


spacecase0

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Re: common design flaws
« Reply #7 on: August 14, 2015, 07:21:58 PM »
Since my charge controller and batteries are both on the same side of the battery protection/fire prevention fuse (60 amp in my case) and the radio is on the other side of the fuse how will the charge controller directly power the radio when the fuse blows?  The charge controller is there to charge the batteries.  The fuse is connected directly to the output of the battery bank with 2" of wire from the terminal to the fuse.  It is there to disconnect the batteries from a hard short that would cause the wiring or the batteries themselves to become hot enough to become a source of ignition or draw high enough current to warp the plates causing the batteries to be ruined.
what you are saying means that you wired your system the correct way,


Tevin

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Re: common design flaws
« Reply #8 on: August 15, 2015, 09:29:34 AM »
To settle my own curiosity, I connected up my Morningstar SunSaver 10 controller (which is considered a "cheapie") to a battery and a solar panel, then measured the output of the controller.

I got about 14.10 volts out, exactly as expected.

I then disconnected the battery to simulate a fuse blowing, but left the solar panel on line. The output of the controller dropped to zero.

This is the way a controller is supposed to work.

I don't mean to be argumentative or start anything, but I'm totally lost on how anyone can say a controller is "is not broken at all" when it goes to a dangerously high output voltage, far above its specified maximum, under any conditions. I'm sticking with my original analysis: Such a controller is either defective, or is so poorly engineered that it should not even be on the market.


« Last Edit: August 15, 2015, 09:32:07 AM by Tevin »

spacecase0

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Re: common design flaws
« Reply #9 on: August 15, 2015, 07:37:21 PM »
I sure see your point, and tend to agree
it is just that there are so many on the market that are not like yours
and I often don't get to choose what hardware is bought before it is bought
also they tend to be the smaller lighter ones, so people get them for portable use,
and then they connect them wrong.
either way, it is an issue that seems like people should think about before they fry a radio if they got one of the "less than ideal" ones

here is a guy that shows the issue with a similar test
page 5 shows the over voltage of the PWM colar controller
http://www.schams-solar.de/download/DESCRIPTION/comparison-mppt-pwm.pdf
now he connected a power supply that is not as current limiting as a solar panel, and that is why he sees what he sees on the scope with the battery still connected

this one sold all over the place has the issue
http://www.amazon.com/Sunforce-7-Amp-Charge-Controller/dp/B0006JO0XI/
have seen it at boating stores, RV stores, harbor freight, ham radio stores, frys electronics...
it has been for sale for many many years and lots of people buy it, and there are many others are designed almost like it
you can usually tell them because they have only solar and battery connections (no load connections)
they have 2 LED lights, a charging and a charged, and they have a cut in and a cut out voltage listed with no option for battery type
when you open them up, they have no inductors and no large heat sinks
also usually no chips at all, discreet components only

they are out there, so watch out for them.

edit:
one more thing,
quite a few solar charge controllers are also positive ground,
I have that seen confuse a few people that expect everything to be negative ground
« Last Edit: August 15, 2015, 07:45:32 PM by spacecase0 »