Anything to make people aware that putting the right size cable is a must.
Not too long ago I was in a shop, someone buying some cable to run an inverter. They wanted X cable to run Y metres to run Z equipment. Over hearing the conversation I said you need a larger cable as you will have at least a 10% loss. Have you checked with a resistance calculator.
I let them know I was there getting heavier cable for my compressors as what I had was not heavy enough.
They didn't want to spend the money to put in thicker wire. No hope!
T1 Terry said
10:26 AM Apr 9, 2019
"They didn't want to spend the money to put in thicker wire. No hope!"
Another one I received early on in the experiments and testing from auto electricians, "You don't need that size cable for solar, this is what we use and came out with a roll of 6mm auto cable. When I said that would not carry the current over the 10 mtr run he laughed and said "who told you that, this is 4.35mm sq cable and solar installers only use 4mm sq cable. Look on the roll, rated for 50 amps" What do you do when faced with that sort of "clever" from someone who should know better.
T1 Terry
Whenarewethere said
11:25 AM Apr 9, 2019
This was at a business who's name started with J. I had a go at them for exactly that, the amp rating on the roll of cable. It is a meaningless statement at best. Maybe some lawyers could earn some money here!
50 amps over a roll of cable & one will be battling to charge a high speed mobile!
Bring back: Hung, drawn & quatered. It might just send a subtle message!
As I have said a few times. I have less than zero experience in solar (low voltage) & it is frightening the the apathy, disinterest & blindness out there. Do some research, it is all on the internet, it is not difficult stuff! Minimal thinking & effort will keep your fridge going in the Pilbara!
At least I got the wiring right, but have replaced a lot of hardware due to Fu--ups by manufacturers trying to flog off products not fit for remote outback.
What is 50amp cable fit for? Even my young nephew can work that one out. NOTHING !!!!!!!
If you are flogging off a caravan, at the very least go back to pre-school & do some basic maths (or math as a current PM calls it!)
I do sincerely apologise for the extended rant.
oldtrack123 said
12:55 PM Apr 9, 2019
No need to apologise
I think the big problem with DC/Dc chargers is that many people do not understand physics.
You cannot get more power out than you put in.
Fact, the input power will always be greater than the output power,
Depending on the brand & model some will work down to quite low input voltages [As low as 9V]
But with a 9V input, & output voltage@40A, a 40A charger could be pulling in excess of 65A .
That means 6B&S just to handle the current without overheating the cables
So not only cable, but spare alternator capacity has to also be considered[spare capacity above the usual loads on the alternator]
-- Edited by oldtrack123 on Tuesday 9th of April 2019 01:00:29 PM
T1 Terry said
01:40 PM Apr 9, 2019
6mm auto cable (the stuff they claim is 50 amp rated) is great for linking solar panels to a junction box as long as the panel is no more than 150w nom.12v, higher voltage can handle more solar capacity, but most of what we do for RV stuff is 12v nom. The 50 amp rating is good because it allows us to use 40 amp DC double pole circuit breakers on each 6 B&S cable run from a terminal strip in the junction box. The circuit breaker will trip before the current reaches a point were the cable insulation may fail, yet the 4.35mm sq conductor can carry the max expected 10 amps with very little voltage drop over the max 5 mtr any run on an RV roof would be., so it suits that purpose just fine.
T1 Terry
T1 Terry said
02:03 PM Apr 9, 2019
oldtrack123 wrote:
No need to apologise
I think the big problem with DC/Dc chargers is that many people do not understand physics.
You cannot get more power out than you put in.
Fact, the input power will always be greater than the output power,
Depending on the brand & model some will work down to quite low input voltages [As low as 9V]
But with a 9V input, & output voltage@40A, a 40A charger could be pulling in excess of 65A .
That means 6B&S just to handle the current without overheating the cables
So not only cable, but spare alternator capacity has to also be considered[spare capacity above the usual loads on the alternator]
-- Edited by oldtrack123 on Tuesday 9th of April 2019 01:00:29 PM
A lot of DC to DC chargers will reduce their output current to limit the current the input side needs to handle. It looks like it is being kinder on the supply system, but in truth it is self protection. Some do it by current monitoring, others by heat produced on the input side, the current measurement method works the best to save the damage to the DC to DC charger.
Some are a tad over rated to their actual continuous output rating, ok for smaller lead acid batteries but big lead acid battery banks and lithium battery banks need to be aware of the problem and select the power supply setting to limit the output so it reduces the strain and heat generated inside the DC to DC charger.
Vehicles with smart alternators and long runs from the battery to the towbar, like the Chev Silverado, require 2 B&S cable for the supply side of the 40 amp units, roughly 30mmsq where 6 B&S is around 13.5mm sq. The voltage drop was so serious the units would turn on and then turn off a few seconds later once the engine had been running for more than 20 mins. seems the battery/alt voltage dropped to 13v or less no matter what load was on the charging system.
T1 Terry
Extraordinary Rendition said
10:48 PM Apr 10, 2019
It would take less time than it takes to post opinions here to aquaint ones self with the theory behind what you are trying to achieve. It is High School Physics; Ohm's Law. Resistance of a conductor .. rho l / a . Dont pet the sweaty things.
Phillipn said
09:20 PM Apr 11, 2019
A bit of light reading. Go to the section on wiring.
A bit of light reading. Go to the section on wiring.
Hi Phillip
I give that my tick of approval
It is pretty well consistent with what many of us advise.
It is a bit out of date though as it does not take into account "smart alternator"? & for which there are very, easy, cheap solutions, far far cheaper than a DC/DC charger
T1 Terry said
03:03 PM Apr 12, 2019
oldtrack123 wrote:
Phillipn wrote:
A bit of light reading. Go to the section on wiring.
Hi Phillip
I give that my tick of approval
It is pretty well consistent with what many of us advise.
It is a bit out of date though as it does not take into account "smart alternator"? & for which there are very, easy, cheap solutions, far far cheaper than a DC/DC charger
You aren't suggesting people should interfere with the computer management that was tuned to control emissions and fuel consumption are you
But on a more serious note, I wonder if the replacement fuse idea has any affect regarding warranty if an alternator fails, they are mega expensive in the newer vehicles
https://www.redarc.com.au/images/uploads/files/news/installing_dc-dc_chargers_ind.pdf
A good read,, thanks Pete
Anything to make people aware that putting the right size cable is a must.
Not too long ago I was in a shop, someone buying some cable to run an inverter. They wanted X cable to run Y metres to run Z equipment. Over hearing the conversation I said you need a larger cable as you will have at least a 10% loss. Have you checked with a resistance calculator.
I let them know I was there getting heavier cable for my compressors as what I had was not heavy enough.
They didn't want to spend the money to put in thicker wire. No hope!
Another one I received early on in the experiments and testing from auto electricians, "You don't need that size cable for solar, this is what we use and came out with a roll of 6mm auto cable. When I said that would not carry the current over the 10 mtr run he laughed and said "who told you that, this is 4.35mm sq cable and solar installers only use 4mm sq cable. Look on the roll, rated for 50 amps" What do you do when faced with that sort of "clever" from someone who should know better.
T1 Terry
This was at a business who's name started with J. I had a go at them for exactly that, the amp rating on the roll of cable. It is a meaningless statement at best. Maybe some lawyers could earn some money here!
50 amps over a roll of cable & one will be battling to charge a high speed mobile!
Bring back: Hung, drawn & quatered. It might just send a subtle message!
As I have said a few times. I have less than zero experience in solar (low voltage) & it is frightening the the apathy, disinterest & blindness out there. Do some research, it is all on the internet, it is not difficult stuff! Minimal thinking & effort will keep your fridge going in the Pilbara!
At least I got the wiring right, but have replaced a lot of hardware due to Fu--ups by manufacturers trying to flog off products not fit for remote outback.
What is 50amp cable fit for? Even my young nephew can work that one out. NOTHING !!!!!!!
If you are flogging off a caravan, at the very least go back to pre-school & do some basic maths (or math as a current PM calls it!)
I do sincerely apologise for the extended rant.
No need to apologise
I think the big problem with DC/Dc chargers is that many people do not understand physics.
You cannot get more power out than you put in.
Fact, the input power will always be greater than the output power,
Depending on the brand & model some will work down to quite low input voltages [As low as 9V]
But with a 9V input, & output voltage@40A, a 40A charger could be pulling in excess of 65A .
That means 6B&S just to handle the current without overheating the cables
So not only cable, but spare alternator capacity has to also be considered[spare capacity above the usual loads on the alternator]
-- Edited by oldtrack123 on Tuesday 9th of April 2019 01:00:29 PM
T1 Terry
A lot of DC to DC chargers will reduce their output current to limit the current the input side needs to handle. It looks like it is being kinder on the supply system, but in truth it is self protection. Some do it by current monitoring, others by heat produced on the input side, the current measurement method works the best to save the damage to the DC to DC charger.
Some are a tad over rated to their actual continuous output rating, ok for smaller lead acid batteries but big lead acid battery banks and lithium battery banks need to be aware of the problem and select the power supply setting to limit the output so it reduces the strain and heat generated inside the DC to DC charger.
Vehicles with smart alternators and long runs from the battery to the towbar, like the Chev Silverado, require 2 B&S cable for the supply side of the 40 amp units, roughly 30mmsq where 6 B&S is around 13.5mm sq. The voltage drop was so serious the units would turn on and then turn off a few seconds later once the engine had been running for more than 20 mins. seems the battery/alt voltage dropped to 13v or less no matter what load was on the charging system.
T1 Terry
A bit of light reading. Go to the section on wiring.
Hi Phillip
I give that my tick of approval
It is pretty well consistent with what many of us advise.
It is a bit out of date though as it does not take into account "smart alternator"? & for which there are very, easy, cheap solutions, far far cheaper than a DC/DC charger
You aren't suggesting people should interfere with the computer management that was tuned to control emissions and fuel consumption are you
But on a more serious note, I wonder if the replacement fuse idea has any affect regarding warranty if an alternator fails, they are mega expensive in the newer vehicles
T1 Terry