Quadruped Robot for monitoring terrain humidity

@davee Many thanks for your suggestions.

A small note however: I'm powering this project with NiMH batteries rather than lithium for safety reasons.

Do you think I would still need a fuse?

Have a nice day

Hi @valerio,

re:

I'm powering this project with NiMH batteries rather than lithium for safety reasons.

Do you think I would still need a fuse?

Contrary to popular belief, most fuses (and their close relations/replacements like circuit breakers) in power distribution applications are employed to prevent power distribution wiring overheating, and becoming a fire risk.

They are rarely employed to protect the actual equipment being powered at the end of the wire, though any protection they provide to it is welcomed as a 'bonus'. Equipment that is powered is expected to provide its own protection against overheating, etc. due to internal faults and so on.

(Protection devices (fuses, etc.) within electrical/electronic units will be designed to deal with specific threats, which may include reducing damage to the unit, as well as protecting wiring - that is a much more complex story.)

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On the basis you have already suffered a small amount of damage by wiring from the battery overheating, I tend to think you have already proved the need for protection which covers all of the wiring, starting as close to the battery as reasonably possible. I picked out lithium batteries, as even physically small cells can supply large currents, but larger NiMH, lead acid and so on batteries can also deliver high currents. In addition, many batteries can explode if shorted.

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So I would say, you definately need an effective protection device, and an appropriate fuse would be high on my list of options to achieve a  reasonable compromise of safety, complexity, cost and so on.

We all do things hoping for the best outcome ... but we also need to look at what we we are doing with pessimistic eyes, and try to imagine what could go wrong ... and look for ways of preventing or mitigating the consequences ... we will never cover every potential problem, but we can push the odds of a catastrophe in our favour.

Best wishes; have a safe and happy day! Dave

@davee A fuse or breaker is put in a circuit to prevent bad things happening due to overheating. This is often quoted as preventing the wiring insulation from catching fire but that is a little simplistic for electronics projects, more of an electrical system thing. What I do is figure out what the maximum current is for normal operation then add a fudge factor. Many use 125% of normal. Even amongst us electricians you will get many debates over fusing. When I built my solar system I put fuses or breakers everywhere but I am still not happy becasue I don't have one connected directly to the +ve battery post. I have a 200A but that gets warm when the charger is full on and when the ambient temp is high 20's/80's then I do not like the temperature of the fuse. TBH, I had forgotten about it and now thanks to this thread I will resurrect that task of finding a better solution.

Hi Ron @zander,

   I am rather familiar with protection devices, from both system and unit perspectives. I was trying to keep it 'simple' ... my sermons are too long at the best of times.

I did (briefly) try to tried to distinguish between protection in power distribution, from that of protection found inside a unit that consumes power.

Although the battery wires are only 'short' in conventional distribution terms, I felt their role was still that of power distribution ... and with power distribution. protection of the wiring is the first priority.

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The selection of protection device, is a whole new story. Again, I tried to keep to one step at a time, and I concentrated on answering, 'Do I need a protective device?'

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Moving to the next question,

You mention, a 125% normal guidance rule ... this sounds plausible, if a little on the low side, as it might be liable to occasional failures, if you are talking about UL rated fuses, which I guess is most likely if you are based on the American continent.

As you are probably aware, the conventions of how to rate fuses is extremely diverse on the international scene, and close examination of fuse rating detail definitions are occasionally contradictory within the same standard.

In addition, not all loads are 'well-behaved' resistors ... many have high peak demands, typically at switch on. These peak demands tend to stress and prematurely age fuses. Of course, there are 'slow blow' fuses which attempt to allow for such demands.

It even depends upon the 'cost' and 'consequences' of having a fuse blow prematurely .. luckily, low cost and easy to fix for a project on the bench. So 125% guidance rule here, might be fine ...

And, as you mention, high current fuses can dissipate (lose) a significant amount of power in normal use. Alternative techniques, including circuit breakers and solid state power controllers, can overcome this and other downsides of fuses, but are generally more expensive and may need provision for testing and even failure of the protection device (when it fails to protect the circuit) itself.

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For a project involving motors, it may be quite difficult to determine the current demands ... I suspect a semi-empirical approach may be called for ... but I think the first rule is the fuse should blow before the wiring gets dangerously hot ... even if that means the wiring has to 'upsized'  to match the smallest fuse which doesn't blow in normal usage.

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Sorry, if this sounds a bit sermon-like, but I hope it is of interest and helpful.

Best wishes to all, Dave

@davee Not a sermon at all Dave, just good data. Yes my 125% was a little off the cuff. It is subject to me not knowing the 'normal' and I was remiss in not pointing out it was for resistive loads. For any non-resistive loads 150% is more reasonable assuming that is inside the wiring spec and many motors will be best served with that fuse/breaker being of the slow blow variety.

I recall a very spirited debate in the RV community to do with solar installations. For instance my 'normal' load as I sit here with no appliances on or even the TV is 100W - 120W but if I want to top up my 7,200 WH battery bank I will add 1,440 Watts to the wires going from the inverter/charger to the battery bank. That is closer to 1500% than 150% so local knowledge is also important. Now that might sound like the end of the story, but my particular inverter has a feature that allows me to add 2,400 Watts to the AC side which means those battery wires now have to handle worst case 2,400 Watts or 200 Amps. I use 4/0 welding wire and a special 400A fuse. In this case I didn't go above the max since I can not conceive of anything drawing that much power under normal conditions (W/D and 1 A/C on other leg) so this is the oft quoted wrench across the battery posts scenario. This is why I NEED to get that disaster fuse installed on the battery post because at the moment I have an exposed post and no fuse between it and ground. It is in a box but still not good enough.

NOTE: Just to clarify. Normal RV hookup is to 2x50A service, but if I had to settle for a 1x30 and then did something to draw 50A I would need that 20A boost. Not very common, but certainly not unheard of in the summer with 2 A/C units running plus W/D and microwave. You would be surprised or maybe not how many RVers have no idea that a 50A post is 12,000 watts of available power (2x120x50) while a 30A post is 3,600 (1x120x30). Many think the 30 is 60% of the 50 hence the lengthy discussions on inverter wiring techniques etc.

@davee I concur with everything you have mentioned about circuit protection devices.. coming from an industrial background, I can appreciate the how the cost of not providing protection, especially with power distribution systems, can be very costly, as well as dangerous. You just haven't lived until you have endured a 480 Vac motor starter blowing up and spitting out a fire ball that reaches the temperature of the sun in about 200 mS..not to mention all that copper and metal splatter that if you were unfortunate enough to be in the path of, can ruin your day, forever!  Even small energy sources like batteries, can cause significant damage, so the question is not whether or not you should use fuses or circuit protection, but rather what type, and where they should be employed.. just my two cents worth of my experiences with the problems that come along with power system safety, and how to eliminate or mitigate  those potential problems.

Safety is # 1 priority when it comes to electricity.. well, that's my sermon for the day... lol

Stay safe, and have fun..

kind regards,

LouisR

@inst-tech

Posted by: @inst-tech

You just haven't lived until you have endured a 480 Vac motor starter blowing up and spitting out a fire ball that reaches the temperature of the sun in about 200 mS

Reminds me of the days doing maintenance in the foundry at the place I worked, dodging molten gunmetal bullets at random 🙂

Posted by: @inst-tech

Safety is # 1 priority when it comes to: ...

Everything!

@zander @davee @inst-tech

Today the robot moved its first steps.

It is very slow because it doesn't have a lot of traction on the floor, but it moves without major issues.

I'm really happy I managed to make it work.

@valerio Good job!.. your making progress, and inspiration to the rest of us working toward making our robot do what we intend for them to do...

regards,

LouisR

@frogandtoad yep... been there, got the hat and the T-shirt..Worked maintenance for over 30 years, mostly in power and utilities part of the mill, but had over 15 years of construction experience, and 4 years in the US. Navy working in EWS ( Electronic weapons systems) so seen a lot that can, and does go wrong from time to time..safety is not a choice, it's a must do thing, if you expect to go home with everything in tacked.

Glad you didn't end up a victim of those molten "bullets"..lol  

Regards,

LouisR

@inst-tech @davee @zander

After some extra tweaking, the robot now moves a bit faster and is more steady.

Here is a picture of it (I cannot send a video because the size is too big).

@inst-tech

Posted by: @inst-tech

@frogandtoad yep... been there, got the hat and the T-shirt..Worked maintenance for over 30 years, mostly in power and utilities part of the mill, but had over 15 years of construction experience, and 4 years in the US. Navy working in EWS ( Electronic weapons systems) so seen a lot that can, and does go wrong from time to time..safety is not a choice, it's a must do thing, if you expect to go home with everything in tacked.

Glad you didn't end up a victim of those molten "bullets"..lol  

Regards,

LouisR

Thanks Louis, and no worries! - Safety is always my motto, and number one priority!  Since my lovely EWP (Engineering Workshop Practice) teacher came up behind me one day and virtually ripped the hair off my scalp (I doubt any snowflakes would accept such actions these days) for using a drill press, warning me that this and worse might happen if you don't wear a hair net - That was my first year in secondary school!  Thereafter, as a qualified Toolmaker, I helped design and build many foundry patterns, press tools, injection molding dies, etc... I specialised in Tool and Gauge making, and ground the microns out of them all 😀

I love Engineering, designing and making all kinds of stuff!

Cheers

PS: - I have witnessed some really bad injuries around machinery, so please do not discard the importance of safety!

@frogandtoad I have had a few close calls with a shaper, wood lathe, chain saw, and thanks to a former brother-in-law 240VAC. At 80 I think I have skated past all the danger spots. These little critters like UNO's etc don't bite nearly so hard.

 Just to show how I have gotten wiser as well as older I took Bill's advice and bought both the 1:1 isolation transformer (WOW expensive) as well as a 24VAC transformer to be able to 'play' with AC devices.

@zander Good call Ron, it's better to start thinking safety before it bites you in the rump...

It only takes about 9 mA to stop your heart! So even at relatively low voltages, if your body resistance is low, you can get a shock, albeit, not enough to seriously injure you, but can make you tingle...hehe

I once was shocked by 5000 vdc from an electrolytic capacity bank because I didn't use the shorting probe to discharge the caps when removing a transmitter power supply.. they never had to remind me again!..That was while I was in the Navy, and barely 6 months into my job working on D.A.S.H. drone helicopters transmitter gear.. Oh, I've done some stupid things in the past, and was lucky.. but the longer I was a tech, the more respect I had for safety, ..In 30 years at the plant, I had a perfect safety record..of course, we had a very excellent safety program at the mill, and the training we received was way above what many in the industry received as normal..  I'm now 75 yrs old, and would like to reach 80.. but like you, it's gets tougher every day..but it beats the alternative lol

Glad you made it this far, and hope to see you make it as long as you want to..

kind regards,

LouisR

@frogandtoad  Me too!  seen more death and seriously injured people than I care to remember..

Right now, I'm focused on staying on this side of a dirty bed, as I need to take care of my wife who is recovering from back surgery.

BTW..working on an algorithm for PID and a way to decelerate my tank robot as it approaches objects.. got a lot of info from @BRIANG  on his robotics programming series..making a little progress.. 

regards,

LouisR