When figuring out what wire thickness to use...

BeanieBots

Moderator
Agreed westaust.
More to the point, hopefully there is a better understanding of basic "Ohm's Law" a lack of which led to the question in the first place.

Without "Ohm's Law", everything electrical will be a mystery.
 

manuka

Senior Member
BB: Yes- 100s of V (as mentioned) would naturally be needed if currents are going to be manageable. I'm most familiar with the ~270V Toyota Prius hybrid, which uses a NiMH battery -pix below. In fact the the Prius does NOT have a separate starter motor like a normal car, using it's big e-drive motor (running from the ~273V drive battery) to start the petrol engine.

Given long established 230V (of course AC) technology, it's feasible DC car voltages as high as this level may be considered for at least emergency starting, although even a "mere" 42V is potentally lethal under damp conditions. The mind boggles -I wouldn't like a hybrid battery getting up to mischief in a rear end collision either...
 

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BeanieBots

Moderator
That's why as far as "42v" is concerned, I'll believe it when I see it.
Besides, anyone who uses "artistic liscense" to call a 36v battery "42v" with some hope of making political smoke cover the claims of the "increased" voltage is clearly an Artist and not an engineer.
To deliberately confuse something which is already not a standard is NOT the way to get it introduced as a standard.

Besides, what does it REALLY offer?
As you say, 42v is regarded as lethal and is covered as such by legislation.
24v is still regarded as safe and offers almost the same benefits as well as already being common in many larger vehicals and boats.

Going to the much higher ~300v range already used by many hybrids offers far more. Besides, countless tried and tested circuits together with appliances are already in existance for such voltages.

When was the last time your aircon was run off the 12v system?
These are taken from the engine drive for obvious reasons. If a mobile home is what's wanted, then make a mobile home, complete with domestic mains supply to use domestic appliances.

Just can't see "42v" catching on.
MY oppinion. I'm sure others will have theirs.
 

Andrew Cowan

Senior Member
Do hybrid cars have ciruit breakers on the battery (for the drive motor)?

Just wondering about manukas point on rear-end crashes.

A
 

No0bert

Member
Prior to posting this on this forum, many electronic gurus have told me to wire two 12v SLA batts in parallel, but charge them individually, everyone here is telling me this will decrease the battery life. So I am guessing I am to wire it in series, I am definitly going to use around 10-16 AWG wire, and a minimum of a 50Amp fuse, since wheelchair motors can draw up to 35 Amps. Is there a con to having an extremely high current rated fuse?
 

Wrenow

Senior Member
When was the last time your aircon was run off the 12v system?
These are taken from the engine drive for obvious reasons. If a mobile home is what's wanted, then make a mobile home, complete with domestic mains supply to use domestic appliances.
.

BB - You have not seen the 12vDC A/Cs and heat pumps? There are more than one manufacturer, but one is here:http://www.airv.carrier.com/details/0,2806,CLI1_DIV46_ETI9772,00.html

The RV community has lots of appliances available in 12vDC.

Yes, if you design an A/C unit in from the start, it is more efficient/elegant to put the compressor on the engine and run it off a belt. But, if doing aftermarket, it is often easier/more elegant to have a self-contained unit that you just tie in to power.

Been looking into these for adding A/C to my elderly step van (Texas summers get a tad warmish at 40+C).

Cheers,

Wreno
 
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Dippy

Moderator
I think you'll find that BB was on about standard fitment Aircon in cars.
My only experience has confirmed BB that the compressor drive is mechanical with a clutch.
I haven't studied every car in the world. I'll leave that to one or two Forum specialists with plenty of spare time ;)

You know who you are ... so get Googling!
The better ones won't need to Google, as they have known the answer all along....
 

westaust55

Moderator
I think you'll find that BB was on about standard fitment Aircon in cars.
My only experience has confirmed BB that the compressor drive is mechanical with a clutch.
I haven't studied every car in the world. I'll leave that to one or two Forum specialists with plenty of spare time ;)

You know who you are ... so get Googling!
The better ones won't need to Google, as they have known the answer all along....
your right with how they work Dippy.
And Peltier devices (totally electronic) consume too much power to be useful as heat pumps for vehicle air conditioning systems
 

BeanieBots

Moderator
many electronic gurus have told me to wire two 12v SLA batts in parallel, but charge them individually
And now you've been told something different. Life's confusing isn't it:confused:

Go ahead, play, learn, read and understand. Then you will "KNOW" for yourself. It's called experience.

50A fuse with the batteries in series....
I don't think so. Now YOU explain why not.

TIP: Use the information posted here and not what your "guru" classmates have told you.



@Wrenow,
I was specifically talking about standard fit as "42v" was being proposed as a new standard. For custom retro-fits, then standard is out the window anyway.
Don't forget to upgrade the alternator!
 
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jglenn

Senior Member
You can get shocked when you change the fuse, if a hot circuit.

Also if you use AC 120V fuses for DC, they will not act exactly right, might be better to use DC fuses, they tend to be thicker.
 

Andrew Cowan

Senior Member
And don't get car fuses from the pound store/dollar store. The set I bought seem odd - a 75A fuse is thinner than a 20A fuse... Incorrect labling, I think...

A
 

BeanieBots

Moderator
Andrew, gauge is NOT an indicator of rating. Fuses use different wire type to get different time delays as well as current ratings.

Get yourself a set of glass fuses. Ultra fast, fast, quick, slow, very slow, anti-surge and a few other types all of the same current rating and have a close look inside. You will see a large range of different wire gauges used.
 

No0bert

Member
Could I have a circuit breaker instead of a fuse, I think they do the same thing. Here is a quote from the email:

"The 1100 battery harnesses were made of 10 gauge wire, the unit used 7.5A fuses, and the batteries were Group 24 (deep cycle) batteries, which are (approx.) 70AH, 12 volt batteries. It could use either Gel or AGM batteries, as long as they are deep cycle, sealed batteries."

"There were no fuses in the battery circuit (the fuse was used in the charging system), only a 50A circuit breaker, and it did use 2 12 volt batteries."

2 12v group 24, 70AH batteries... that's like $300 :/. I will most likely not use nearly this much amperage.
 

westaust55

Moderator
Could I have a circuit breaker instead of a fuse, I think they do the same thing.
A circuit breaker and a fuse are significantly different devices but both have the same purpose - to disconnect a supply when there is an overload.

A fuse is a one-time disconnect device whereas a circuit breaker has a life of many disconnects and can even be used as an ON/OFF switch in some cases.


The time-current curves are generally also differnet.

A circuit breaker will have a rated number of operations when switching at normal currents but have a much reduced number of operations when switching at high falut current levels.

Then there are devices that look like circuit breakers but are really just a switch with no protection (tripping) element.
There have about a year ago been cases where counterfeit CB's with a major European manufacturers logo were distributed out of China that only had a piece of wire internally between the two terminals :eek: (not even a switch!)
 

BeanieBots

Moderator
I heard about that one too westy:eek:

IMHO, go for circuit breaker if you can afford them.
You can more precisely specify in-rush trip, thermal oveload trip and depending on type (as pointed out by westaust) use them as a switch.
Some are even adjustable.
Also saves always having to carry a spare fuse!
 

Andrew Cowan

Senior Member
Circuit breakers are much simpler and easer to use (no changing fuses). The only downside is the cost - some high current circuit breakers can be very expensive.

A
 
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westaust55

Moderator
Circuit breakers are much simpler and easer to use (no changingg fuses). The only downside is the cost - some high current ircuit breakers can be very expensive.

A

Sometime the fuse is soldered onto the PCB (eg PC motherboards have fuses soldered in place for USB port protection).

Then after you have replaced the fuse a number of times, particularly if paying a tradesman to do the task at say 50 Pound or say AUD$100 per hour (or part thereof) for each call out, then which is the cheaper option.
 
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