I'm curious to know at what point I need to upgrade my electrical system, mainly the battery and alternator. Right now I have 3 amps for my stereo and a head light harness going straight to the battery. I will soon be adding 7 lights on my roof rack, a winch, some led rock lights and eventually an air compressor(and probably some more things in the future). My main question is how much can a stock battery and alternator setup take before I start overloading it? And if I need to upgrade it what is the most cost effective way of doing it?
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Electrical Question
- Thread starter CTRacing
- Start date
5-90
NAXJA Forum User
- Location
- Hammerspace
Depends.
If you plan on having the engine running with all this stuff going, get as much alternator as you can afford. Upgrade your mains and fusing accordingly (yes, there is a fuse between the alternator and the rest of the vehicle.)
If you plan on running this with the engine off more than the engine running, you're wanting deep cycle auxiliary battery(ies) on an isolator of some variety, so you can power them with the engine off and not touch your starting battery. Accessories would then be wired to the auxiliary battery directly, so they're "behind" the isolator.
How much to get depends, more than anything else, on what you can afford.
If you plan on having the engine running with all this stuff going, get as much alternator as you can afford. Upgrade your mains and fusing accordingly (yes, there is a fuse between the alternator and the rest of the vehicle.)
If you plan on running this with the engine off more than the engine running, you're wanting deep cycle auxiliary battery(ies) on an isolator of some variety, so you can power them with the engine off and not touch your starting battery. Accessories would then be wired to the auxiliary battery directly, so they're "behind" the isolator.
How much to get depends, more than anything else, on what you can afford.
joe_peters
NAXJA Forum User
- Location
- Grants Pass, OryGun
Dang! I had some really cool ideas on upgrades for your year/engine, but then I realized I don't know what year/engine you have. Imagine that! :doh:
joe_peters
NAXJA Forum User
- Location
- Grants Pass, OryGun
The bulk of this article is discussing Renix (87-90) XJs, but the wiring upgrades are necessary on all XJs and there is a section lower on the page discussing the later model PDC-type XJs and how to work with those.
http://www.olypen.com/craigh/charge.htm
http://www.olypen.com/craigh/charge.htm
cruiser54
NAXJA Forum User
- Location
- Prescott, Az
Great link, Joe. Thanks.
AnarchyJet
NAXJA Forum User
- Location
- Wisconsin
Add a volt meter. When it starts dipping below 13.5 volts while running you need a bigger alternator.
5-90
NAXJA Forum User
- Location
- Hammerspace
NB: Alternators are good for 40-45% of max output at idle. You can't get full output out of one until 3200-3500rpm at the spindle (1200rpm or so at the crankshaft) - so just because you're losing voltage at idle doesn't mean your alternator isn't totally up to the task - you're just overtaxing it at idle. Ramp your rpms up a bit, and you should see it recover.
joe_peters
NAXJA Forum User
- Location
- Grants Pass, OryGun
You have to add up the draws of your particular accessories.
A quick and dirty test is if the headlights go out when you turn on your sound system's amp, you need more power.
- Location
- Rainy side of Washington
The answer to that question ranges from "very" to "a brilliant work of fiction" depending on whether you have the blower on, what speed it's on, whether the interior lights are on, whether the A/C just kicked in... etc. The dash gauge is a worst-case meter at the very end of a chain of power wires, each exactly the size it needs to be for the vehicle to work and no larger. If you want a good measurement, add a new gauge that's tied directly to the battery terminals.
jeeperjohn
NAXJA Forum User
- Location
- Temecula, CA
Measure the amperage in the main power wire from the alternator with all your accessories on and the engine running at around 1500 RPM. If you measure more than about 80% of the stock alternator's output then you need to upgrade.
cruiser54
NAXJA Forum User
- Location
- Prescott, Az
I just made up a set of new battery cables for my MJ yesterday. I used #2 cables for the positive and negative and a #4 to the relay near the battery. Kinda glad I did. I found that when my oil filter adapter was leaking in the past, that the oil got into the harness which held both pos and neg cables. The insulation on both cables was all puffed up and deteriorating. Coulda been a major problem down the road had they shorted together. FWIW, before embarking on this project, I was monkeying around and decided to add a ground strap from the dipstick tube stud over to the right inner fender where there's an unused stud. Definitely helped with cranking speed upon starting. Can't have too many grounds and these vehicles were sorely lacking in that department.
joe_peters
NAXJA Forum User
- Location
- Grants Pass, OryGun
Gotta love the Renix!
Did you replace the head to firewall strap with a cable?
I moved my dipstick grounds to the engine block with the negative main cable.
When you put in the 4 ga from the alternator to the PDC lug on the starter relay, did you put in a fusible link? ANL with a holder is the way to go, and you want it slightly greater than the max output of the alternator.
Have you seen this article: http://www.olypen.com/craigh/charge.htm
Did you replace the head to firewall strap with a cable?
I moved my dipstick grounds to the engine block with the negative main cable.
When you put in the 4 ga from the alternator to the PDC lug on the starter relay, did you put in a fusible link? ANL with a holder is the way to go, and you want it slightly greater than the max output of the alternator.
Have you seen this article: http://www.olypen.com/craigh/charge.htm
