Electrical power draw

**Tins** · 29th May 2017, 08:38 PM

Originally Posted by Homestar

Remember that you would rarely - if ever, use all of that at once. The maximum demand of the vehicle would be around 50 amps leaving plenty up your sleeve. Even if you occasionally run over 120 amps for a short time (which I would doubt) it isn't going to hurt anything (as long as all your wiring is in good condition) but just draw down your battery a few amps - and that's a big if IMO - I used to max out my old 35amp alternator on my Subaru occasionally on a cold wet night with my upgraded headlights and spotties on - the charge light would but I could still drive it the 45 minutes home from work after afternoon shift and start it again fine the next day.

I wouldn't worry about the alternator size at all - just make sure the wiring to the high load devices you are adding is up to scratch.

Have to agree. Also, what stereo are you running if you expect a 10a draw from it?

Gav's Scooby had a 35a altar ator. When was the last time a LR had something below 80a? As Gav also says, that's what the charge light is for. Sure, most times you see it it's telling you your alternator needs help. That's because, most of the time, it doesn't.

**ballbag** · 29th May 2017, 09:22 PM

Yeah, wiring will be sufficient.

All estimates I made above are what I'd expect worse case, I know actual use will usually be lower.

I do run all of those concurrently through winter which is why I need to ensure the extra 25 amp load won't be too much.

Point of interest - high beams + 3 x 70w spotties knocks 0.5V off the charging circuit.

Thanks all for the input.

**sierrafery** · 29th May 2017, 09:27 PM

It's not about capacitors, when the alternator's own regulation is sensing the higher draw it increases the ouput and vice-versa:

Originally Posted by RAVE; Elecrical library - Description and operation - Starting and charging - 4.43

.....
When the battery is at a low state of charge or the current draw from the electrical functionsof the vehicle causes a voltage drop, the alternator/ generator automatically charges at its maximum rate (dependant on rotor speed) until 14+ Volts is reached. When demand on the alternator/generator falls, the current output is reduced.

**ballbag** · 30th May 2017, 01:22 PM

Test 1:

Vehicle off, ran Chinese spec 300W snow-gear drying box (to be sexed up with marine carpet if trials prove successful) off second battery. 16 amp battery charger connected to starting battery.

Result 1:

Flattened starting battery in about 90 mins. Switch on unit crapped out so deleted it. Retired to deck with beer while charger does its work.

**trout1105** · 30th May 2017, 03:22 PM

Have you tried the dryer with the truck running?
A 16A charger has No hope of running something that draws 100A-300A.
From what I have been told the disco alternators put out 130A, So if your dryer is constantly pulling more than 130A it will eventually drain the batteries I would think.

**Homestar** · 30th May 2017, 03:42 PM

Originally Posted by trout1105

Have you tried the dryer with the truck running?
A 16A charger has No hope of running something that draws 100A-300A.
From what I have been told the disco alternators put out 130A, So if your dryer is constantly pulling more than 130A it will eventually drain the batteries I would think.

300 watts, not 300 amps. World out around 25 amps.

Alternator will have no dramas with if while the engine is running.

**ballbag** · 30th May 2017, 04:04 PM

Yeah nah, have not run the dryer with engine yet but did dry a damp T shirt without incident, so results as expected thus far. Will report back with further results.

**ballbag** · 26th July 2017, 09:29 AM

Drying box working pretty well and alternator able to maintain starting battery charge with cabin heater, high-beams and spot lights running. Have run for up to 2 hours.

Isolator for second battery opens and shuts continually if/when drying box and fridge pulls combined voltage below cut-out point, but thus far have not drained either battery below 12.8V standing.

Thread: Electrical power draw

Thread Tools

Electrical power draw

Tags for this Thread

Bookmarks

Bookmarks

Posting Permissions