ADD ONs - and Fuses ?

[expresso]

I have made about 4 ADD Ons since i started - But i never added a Fuse to them before now - -- i am curious to know - If the ADD ON is connected to the Chairs Batteries etc, - Wouldnt it be protected the same way with the Chairs fuse or Fuse or Breaker the chair itself may have

for example - my 105ah pack - i added a Breaker to that - the 45ah ADD ON thats connected to that - does not have a fuse - Would it still be protected from the Breaker i have on the 105ah since its all connected when in use ?

my other chair has lead and the chair has its own breaker - the ADD ON i have there again does not have a fuse - - i have had no issues at all - but trying to be safe - my first ADD ON is now being used by someone else and to be safe - i will add a fuse to her ADD ON - since there was a minor mishap - but no ones fault other than the Tech who changed out her batteries - connected her ADD ON Cable to one battery 12V instead of having 24V output on the cable - it was 12V -

so after that incident - nothing was damaged - i decided to add a fuse to her ADD ON pack -

Back to my question i like to know - on my current ADD ONs with no fuse on them - are they still being protected with the chairs fuse or breaker ? being its all connected anyway - i would think it will react if anything ?

i know its just good practice to add one anyway from now on when building it - and i have added a fuse to my 80ah pack i just done - i like to know if its a big deal that i have to remove my other packs and redo the wiring to add the fuse now - or leave it alone since it all connected - and just from now on add one when i make them as i go ?

[Burgerman]

The fuse on a lithium pack is for 2 reasons.

1. So you dont exceed the packs current rating (C rate x capacity). This isn't a problem usually with an add-on unless its too small.
2. To protect the cables. Why? Because if you were to take 150A through a small cable it will catch fire, melt, burn, and probably short out. So the correct fuse is one that will fail before the cable does.

So what size does the cable need to be on an add-on? It will be safe for about 20 to 40A on a hill. It MAY need to be able to do pulse currents as high as 100A or so.
A 6 mm2 (square mm cross section) cable is what I would use. Or if silicone, maybe a size smaller. That will be adequate for an add-on unless your lead battery is crap!

Remember rule of thumb with pvc cables!
A 2 sq/mm cable can do 20A cont
A 4 sq/mm cable can do 40A cont.
A 6 sq/mm cable can do 60A cont.
A 10 sq/mm cable can do 100A cont. All can do much more for a short time.

A 40A fuse, therefore can protect a 4 sq/mm cable. It can also pass a 150A pulse, a longer 100A pulse, intermittent 60A periods. And 40A all day long.

[expresso]

all my ADD ONs are using 10 AWG wire - i know i know - i dont do well with this 6mm square thing and you dont do well with the AWG size - i think 10AWG is a little over 5 mm sq - under six and over 4 for sure -

the fuse size was not what i really wanted to know - but its good to know - i have used a 50A on one pack and using a 60A on mines to give a bit more slack on hills etc, with the bounder

the question i was asking was - the Pack in the chair is fused - then the ADD ON Cable is connected going out of the chair to my ADD ON pack - One Chair i am using 10AWG wire there also - its all silicone wiring - that runs out of the chair to my ADD ON which is also 10 AWG - all silicone - thats how i done it on my first chair and its been that way for past 3 years no issues

what i wanted to know was since its all connected as one larger pack now - would the fuse or breaker i have - its an 100A on this chair - would that be in effect be working to protect the ADD ON also at the same time when its all Connected in use - ? the wiring on the Breaker on the Chair pack is 8 AWG - so that should be fine there -

two things then

1. Is the whole pack protected when all connected this way with one fuse or breaker on either the Chair or pack in the chair ? the ADD ON itself is not fused -

2. i guess now would be if 10 AWG wire i used on the ADD ON pack is enough to handle a 100A breaker - it may be too large a fuse for the ADD ON then even if its protecting it - it may not because of the size - ?

in this case - it would be better then to redo the wiring on the ADD ON to add a fuse in line like i did on the 80ah ADD ON pack - or Can i leave it alone as is ?


the other chair with Lead - i have a 8 AWG cable going from the lead to the ADD ON - - but the ADD ON itself is using 10 AWG cable for the power - on this chair the chair its self is fused - with a 70A breaker - - again its been 6 years never tripped - and over 3 years with the ADD ON - never tripped.

this all came about because of what happened with the tech installing the cable wrong on the battery - which un aware- the cable was plugged in and got hot fast unplugged very fast and nothing happened - so to prevent that again - first its not my chair and i cant say - mistakes happen either way -

or else i didnt think about it since i felt it was fused already and connected together with the Cable - i am just trying to figure out if i need to do the work and redo it - of its its ok - i am trying to get out of doing more work

[LROBBINS]

10 AWG is 5.26 mm2, so can handle slightly more than 50 Amps continuous, and much higher peaks. A 50 or 60 Amp fuse should pass as much current as that wire can handle, even with peaks of 120A or so, yet would open if there's a short in the wiring or the chair's battery.

[flagman1776]

Not very impressive "technician". Do you connect the add on to the chair through a connector like Anderson SB50? My inclination would be to disconnect the add-on pack until I'd verified the correct connections. Could you attach the add on feed wires to the OEM leads... say with zip ties... so they stay together?
A fuse can't hurt...

[expresso]

10 AWG is 5.26 mm2, so can handle slightly more than 50 Amps continuous, and much higher peaks. A 50 or 60 Amp fuse should pass as much current as that wire can handle, even with peaks of 120A or so, yet would open if there's a short in the wiring or the chair's battery.

Thanks - would you know - i am trying to figure this out - but i am not explaining it correctly maybe - lets put the fuse on the ADD ON pack aside for a moment and think of - Two Packs connected together with a Cable - - One pack in the chair - is either fused or using a breaker - so my main pack is protected

would the ADD ON pack be just as protected if just connected to the Main pack with a Cable and the Main pack is fused etc, ? with no fuse on the ADD ON pack ?


about fuse sizes - my 100A Pilot chair uses a 70A breaker from factory - always has - never tripped -

the 646 chair with Rnet - not sure what it uses since i removed the lead and fuse is heatshrinked - i have to cut it to see -

the bounder chair uses a breaker which is also 70A - one for each motor i believe if i look at the diagram - looks like two breakers - - but either way its 70A - wiring on the bounder is 6 AWG very thick on the battery end and even the balance wires look to be 3x thicker than what we use on the PL 8 balance wires -

back to my question - do you think its Ok to leave the ADD ON alone with no fuse since its connected to the main pack which is fused - or i should just fuse the ADD ON also anyway - i felt since its connected as ONE Pack with a Cable - wouldnt the one fuse i have work for everything thats connected to it ?

[expresso]

Not very impressive "technician". Do you connect the add on to the chair through a connector like Anderson SB50? My inclination would be to disconnect the add-on pack until I'd verified the correct connections. Could you attach the add on feed wires to the OEM leads... say with zip ties... so they stay together?
A fuse can't hurt...

dont know who did it - what tech.but most or idiots - sorry to say - some can be better and are - - this wasnt my chair and i fixed it after the fact. its connected correctly and nothing should happen unless someone is touching it for what ever reason and doing something that would short it .

if it were my chair - First i dont let anyone take my chair - they fix it in my house if it needs it - IF i ever did have to let them take it - my battery pack is being removed before they take it - i will take pictures and document anything that goes wrong - if i get it back with a scratch - i will let upper boss know about it -

these things need to be handled with care - anyway - cable is connected to the lead with ring ends and SB50 on the outside end - - another cable from there goes back to the ADD ON - thats it - it dosnt never need to be disconnected -

it happened to me also when they changed mines a while back - i checked my cable with volt meter - and it didnt show nothing - means it was wrong - i had to point it out and show him - then after a few head scratches - i had to instruct this so Called tech. it got done correctly - i checked it - all good - ok close it up and good bye.

now if i wasnt there - it would have been wrong when i got my chair back - first they dont know - secound they dont check after the fact and third - they dont care - so its up to you to do all the work and checking to be sure - because in the end - its your chair and you will be screwed without one - they go home and call it a day thinking they just saved the planet

its a joke really - i am glad i have one good tech. and i only use that one if anything - i just dont trust the industry - cant even change batteries !!!! - are you kidding me -

[flagman1776]

I would fuse the add on separately. It could be on the chair side of the connector or the add-on side.

[Burgerman]

Expresso. The fuses are there to protect the cable. So the one of the chair protects the chairs cables, in case anything bad happens inside the controller or a cable short etc.

The add-on needs a fuse if you were selling it. At the battery. Since its yours, and you are aware there isn't one you can take the risk or be very careful. But better to have one.

[expresso]

Ok - so its best to just have a fuse period on each pack you build - its not a problem to add a fuse as you build them - i was just trying to understand if i really had to now that they are built and use already - these are all mines - the one Quickie has - i will add a fuse for her also - since what happened with the tech thing.

thats how it all started and i started to think about if for my packs also - So if theres a short on the ADD ON pack - the fuse thats on the main pack which is all connected as one large pack - dosnt matter and wont help the ADD ON pack ?

i will just redo them and add a fuse -

thanks

[Burgerman]

the one Quickie has - i will add a fuse for her also - since what happened with the tech thing.

Thats exactly why you should have a fuse.

[expresso]

yes i agree - better safe - but that only happened because others touched the chair and it was never checked before connecting it again to the ADD ON - but either way - we all make mistakes and i could have easily done the same - but knowing me and how i feel about others touching my chair -

it happens - i was suppose to check it first with my volt meter but for what ever reason - she just decided to connect it before i checked it - i will add them to the my other packs - over the winter - i have time anyway - i have to attach the fuse i made for her pack first with the 2 diodes - and set it up on her new chair so she can leave it there connected all the time -

then that leaves me 45ah pack i have to add the fuse - and the 60ah pack - - then that would be it -

[flagman1776]

Fuses are to protect us from serious consequences possible during "Oh, Shit!" moments. It's like insurance. We can never protect for every danger but we can protect for some known hazards.

[expresso]

yes i agree - why i never ever added them from the start with the ADD ON - i cant recall - i didnt think it was needed - never really discussed much - more concern was the whole chair pack etc, slipped thru the cracks -

i actually went the first Summer with my 105ah pack in my chair with NO Fuse or Breaker - before i figured out it wasnt protected and redid the wiring to add one -

[flagman1776]

While we are talking about fuses... I know my "big" scooter has a breaker between the 2 Group 27 SLA batteries. Why is it BETWEEN the batteries and not on the +24V power out lead? Do they get away with a smaller breaker?
If I were to do a lithium conversion, where should I fuse (breaker) the pack?

[Burgerman]

Between the batteries.

[Burgerman]

In any circuit theres the same amps everywhere. Between the batteries it protects both. If its on the 24V pos, then you can short out the one with no fuse. But either way will work.

[flagman1776]

I see the FMA PL8 charge leads appear to both be fused.

[Burgerman]

Yes. 40A per cable.

[ex-Gooserider]

While we are talking about fuses... I know my "big" scooter has a breaker between the 2 Group 27 SLA batteries. Why is it BETWEEN the batteries and not on the +24V power out lead? Do they get away with a smaller breaker?
If I were to do a lithium conversion, where should I fuse (breaker) the pack?

In theory opening a DC circuit anywhere will disrupt the current flow as the current goes in one side of the battery (pack) and out the other... But ONLY if the short circuit current path includes the fuse... This means that best practice is to put the fuse as close as possible to the supply connections so as to minimize the chance of a short that doesn't include the fuse....

Putting the breaker between the two batteries in our typical two-brick lead setups does a really good job since that is usually a pretty short lead, and is well protected... Plus it protects both batteries as BM said earlier...

In a car where you have a negative ground (so pretty much everything on the car is 'ground') you will most reliably open the circuit if the fuse is next to the plus terminal.... We generally tend to fuse the + side by convention as well, but it really doesn't matter as long as the circuit gets interrupted...

When you have two different supplies in parallel like Expresso is doing with his addon, it gets more complex, and protecting gets more complex...

If the only fuse is between the batteries on the chair, then there is little or NO protection, as the fuse is bypassed by the add-on.... If a short occurs in the wiring between the main batteries and the addon, you might blow the main fuse, but the add-on would still be shorted... If the short happens between the two packs and the rest of the chair, the add-on would not be protected, and might supply enough current to keep the main fuse from blowing... Either way expect lots of smoke.....

If there is a separate fuse on both the main batteries and the add-on, a short would need to blow BOTH fuse before the current stops - since the fuses are in parallel, each is only seeing part of the current, so it might well take longer to have either get hot enough to open, possibly dangerously so...

This means I'd be inclined to make both fuses smaller than I might choose if just running a single set of batteries.... Other than that, it is not really practical to do much about protecting against a short in the wiring between the packs. However it might be a good idea to add a THIRD fuse in the wiring between where the two packs connect and the rest of the chair electrics...

ex-Gooserider

[expresso]

i decided i will add a fuse to my ADD ONs - none of them had a fuse - i will add one on the power line on the ADD ON - like i did with latest ADD ON - so the chair is protected from the factory - and my ADD ON will have a fuse also - - i cant see anything else i can do - other than - add a fuse on the Cable also that connects both Packs -

[flagman1776]

I think it is smart to just go ahead & fuse every add on pack. Add-ons are, by their nature, likely to be switched around between various chairs, yours & others. This way, the add on & it's wiring is protected no matter where it's used on a given day. Include the fuse on any future builds.
If a chair still has lead batteries, the OEM protection should be fine. If you do a LiFePO4 conversion, you'll want to include protection.

[expresso]

yes its all good - i did on my new pack - will do on my other 3 packs - one at a time - before the summer everything will be fused -

its easy enough - i will try to cut the wire and try to add it without making a new cable -

[Scooterman]

Do fuses have resistance, and do they drop voltage across them?

VD = I x R

[Burgerman]

Yes.
Everything other than superconductors at minus god knows what temp, has resistance. Its all a matter of how much.

A fuse is very short. I mean the thin part that melts is. That thin part has a higher resistance than the rest of the circuit or cables which is why it heats up, melts and blows. In one very short spot. Because its so short, a matter of a few MM only, that high resistance point has little effect on the systems voltage. Use your multi meter. Set to resistance. It will typically be way below .1ohm on the size fuses we use. Hard to measure without quality leads and a fancy meter. There will be some slight voltage drop across it, under high currents, since this is why it heats up and blows. Even a solid copper block has resistance. Just not much.

Or think of this. The fuse has higher resistance per inch. But the cables have a lot of inches.

[Scooterman]

Thank you BM that was such a good answer. I'm humbled because you are so clever

[Burgerman]

Not so much clever. More years of blowing stuff up, overloading engines, hobby stuff, destroying stuff on purpose and in error and a bit of physics chucked on top.

An expert is someone that has made every mistake once.
A master is someone that has made every mistake many times over.