Electrical Help

[Grant Lamontagne]

As most of you know, I am not all that good with electricity, so I thought I'd ask for some advice.

It looks like the alternator in my Jeep is dead, and I'd prefer to upgrade it rather than just replace it.  Ideally, I'd like to wire in a second battery, and I have the diagram on how to do that from a Jeep forum, but I' wondering what I should look for in an alternator?

Apparently the stock unit puts out 40-60 amps, and one of the ones I am looking at claims 140-220 amps.  Do I need that kind of power?  Is that respectable enough?  Will it properly charge a two battery system?  Will it affect my fuel economy?  Will my Jeep catch fire and/or explode?  Is there a better choice?

My Jeep has had a rough time lately and it's time for me to start putting some money into it, or I have to make the decision to buy a new one, and I'm not ready for that.

Def

[jzmtl]

Mine has 117 amp alternator stock, you sure yours is that low? I have no experience with 2nd battery so this is only theoretical, but smaller amp only means slower charging, and the power it takes to turn the alternator depends mostly on how much power is being drawn at the time so size of alternator should have negligible effect on your fuel economy.

So I guess it depends on how often will you draw on that extra capacity? If it's just there for backup it probably doesn't matter much, but if you plan to install more electronics a bigger one will help.

[Grant Lamontagne]

The description of the high output alternators I've been looking at say the stock is 40-60 amps, but I really have no idea myself.  I'm going by what I read.

I use my Jeep at work an awful lot, and many times I have my laptop and phone plugged in, plus I have the stereo on, sometimes for many hours at a time.  I generally start the engine on a regular basis to ensure that the battery doesn't completely run down, but I'd feel a lot better if I had more power at my disposal.  There have been a few times I have killed my battery at work by running my 4 ways, my computer and stereo for a little too long.

Def

[derekmac]

For the second battery get a deep cycle battery.  Deep cycles are meant for a constant draw and a charge will last a lot longer than a regular battery.

When charging two batteries you will want a high output alternator as it will have to work harder to charge them.

The further away you mount the second battery, you will want to use a heavier gauge wire to connect the batteries.  Just pickup an amp wiring kit from Princess Auto.  I've found that getting a kit there is usually cheaper than buying wire elsewhere.  They should usually have 4 gauge kits there.

Sent from my Galaxy Nexus using Tapatalk 2

[Grant Lamontagne]

I plan on mounting the second battery next to the first one- there's lots of room there and you can get a dual battery tray to replace the factory single tray.

What defines a "high output" alternator?  For example, what numbers should I look for?

Def

[derekmac]

A stock replacement would probably be 60 or 90 amp, for a high output you'd be looking at 140 and up.  You shouldn't need anymore than 140 though for what you'll be asking of it. 

I think Costco sell Optima red or yellow top batteries, but I can't recall for sure.

Sent from my Galaxy Nexus using Tapatalk 2

[Grant Lamontagne]

Here's what I have been looking at:

Mean Green High Output Alternator

OEM style 81 amp Alternator

Def

[jzmtl]

Sounds like a 2nd battery would serve you well. For your use I don't think an optima is worth it depends on the price, but I'd just get a costco brand.

[Mr. Whippy]

Mean Green.is a topflight alternator.  Agree 140 should be fine.  Those 220 units are used to power accessories like dual winches (front and rear) or single winches in high use settings and even welders!  Most important is perfect belt alignment.

[AimlessWanderer]

Grant, if you're looking at fitting an ancillery battery for non-running use look into a leisure or deep cycle battery. From an ampage perspective you want to be looking at charging amps of approximately 1/3 of the battery capacity. Therefore for a 140Ah deep cycle battery, you want around 50A ... BUT ... that should be over and above your normal ampage for running the Jeep. If standard units are 40A you therefore want a 90A alternator. Another way to calculate it would be take the total Ah capacity for both deep cycle and cranking batteries and divide that by three. Either way, for what you're doing I wouldn't look at going much higher than 90A. It's not worth it and just means that cables/fuses get more expensive plus theres a chance of causing battery damage

Too low an ampage will obviously mean you are not charging efficiently, but too high will reduce the working life of the battery

Hope that helps 

[Grant Lamontagne]

I'm sure it would help greatly if I understood any of it....

Def

[dks]

Also bear in mind that every time you start the car the battery "suffers" a bit and also loses some charge.
So if you are going to start the car and run it to avoid depleting the battery, make sure that the car runs long enough to allow you to cover not only the charge lost before starting the car but also the charge lost to start the car.

If for example you start the car and run it for 5 minutes then the battery will be left with a lower charge than before you started the car, as you will not have had enough time to replace the charge used to start the car. That is why if you keep trying to start the car, because of some problem, the battery goes flat.

The bigger your alternator, the faster the charge will be replaced, so a bigger alternator will do more work in those 5 minutes than a smaller, weaker, one.

I use good quality high capacity batteries, but on diesels, due to the amount of charge needed for each start and the strain this places on the battery, they need to be replaced every about 2 years.

[sardauker]

Just one, maybe stupid, add:

put a switch on the second battery, and/or use it mainly for the appliances, i.e. a small 12->110/220 inverter.

You could use a RV circuit that charges both the batteries, and discharges just the second, keeping the first fresh for the normal car uses.

[AimlessWanderer]

I'm sure it would help greatly if I understood any of it....

Def

PM sent 

[AimlessWanderer]

Additional to pm's ...

Have a look at this and tell me what will actually fit (size wise) ...
http://www.gnbsystems.com/12_volt_multipurpose.php

[tattoosteve99]

Imagine water as electricity. Voltage is like a small hole in water line. Now that same size hole is in a dam and it has more amps (push) behind it. Same size hole just different force. That's the way it was explained to me and it helped.

[16VGTIDave]

Voltage is like pressure.
Amperage is like flow.
Wattage = voltage x amperage.

Grant, I think that you should get your Jeep the highest output alternator you can afford to fit. Then upgrade all the wiring from the alternator to the batteries. Add a deep cycle battery (I prefer Optima yellow top's because they last a very long time) and a battery isolator - this connects between the alternator and the batteries positive terminals and allows you to keep from draining both batteries while charging both of them from the alternator. Then you'd have to move all the expected loads (stereo, power outlets, etc) to the second battery. It sounds more complicated than it actually is. 

Now, just to be a realist, didn't you recently mention having rust issues with the frame on your Jeep? If this is correct, throw some ice cubes into your boxers and carefully reconsider any further investments into your Jeep. Still want to spend money on it? Get more ice. Repeat as required until you change your mind. This will hurt much less than spending every last penny on your beloved vehicle only to loose it to the cancer that rust is. Believe me, I know...

Dave


Sent from my iPad2

[AimlessWanderer]

With all respect I would disagree completely, too big an alternater could adversely affect the batteries. A cranking battery will accept charge at a different rate to a deep cycle battery (cranking tend to be more forgiving), and if you try to "force feed" them you'll just hurt them. 

As for the isolator I would recommend a split charge relay, as there's no worries then about forgetting to turn it on when charging and off to avoid transfer to the cranking battery. A bigger alternator would just mean that heavier cables, connections, fusing and relays are required ... as well as the battery issues.

There's just no benefit in simply going for the biggest possible IMHO.

[Mr. Whippy]

With all respect I would disagree completely, too big an alternater could adversely affect the batteries. A cranking battery will accept charge at a different rate to a deep cycle battery (cranking tend to be more forgiving), and if you try to "force feed" them you'll just hurt them. 

As for the isolator I would recommend a split charge relay, as there's no worries then about forgetting to turn it on when charging and off to avoid transfer to the cranking battery. A bigger alternator would just mean that heavier cables, connections, fusing and relays are required ... as well as the battery issues.

There's just no benefit in simply going for the biggest possible IMHO.

Agree with this. 

Of course, if the rusting problem is bad, maybe going whole hog on this and getting a DC Welder set up for the Jeep is a good option! 



Talk about EDC!

[tattoosteve99]

Another option would be 2 alternators. One for the jeep and the other for the extra battery. More work though as you have to wire it in and add brackets and belt. But just a thought.

[Grant Lamontagne]

Dave, you have a very good point about the rust, and I agree with you to an extent. However, a new vehicle just isn't in the budget right now. Maybe a year or so down the road, but not right now. Ideally I would like to drive this Jeep every day for the rest of my life, and I do form an unnatural bond with things even though I know it's just a piece of machinery.

Besides, I'd rather put $1000 into this one and keep it a couple more years than to have to put down several thousand now and get into a $400 payment each month for a new one.

Def

Sent from my MB860 using Tapatalk 2

[Grant Lamontagne]

Just to give a bit of an update- I have ordered a 117 amp OEM replacement alternator for my Jeep.  I'm not sure if it has an 81 or 117, but the 81 was standard and the 117 was optional on it, so I'm taking the bigger one.  I'll let you know if it catches fire...

Def

[AimlessWanderer]

Good luck mate. Give me a shout if you need anything 

[Grant Lamontagne]

I'm sure I will- but the price was right ($150) for the OEM 117 amp alternator versus the Mean Green ($400) one that produced up to 220 amps.  OEM means no screwing around installing it and no issues with the existing cables too, which is also a huge benefit.

And, as if that wasn't enough, I can pick up the OEM one a few blocks from my house tomorrow morning rather than ordering the Mean Green version from the US and waiting for it.  And I need my Jeep back on the road.  I hate taking the VW to work as it will get the crap kicked out of it.

Def

[AimlessWanderer]

Well, if a standard is 81A and you've gone for 117A - you've got an extra 36A to play with over and above what the Jeep needs. If you're sticking to phone charging, stereo and computer use, and not running winches or other heavy duty ancilleries, you'll still be fine adding in a leisure (deep cycle) battery 

[Grant Lamontagne]

I'd like to add a winch sometime, but my understanding with that is that you only use the winch with the motor running, which I would have anyway without the warning.

Def

Sent from my MB860 using Tapatalk 2

[Grant Lamontagne]

Well, the new alternator is in and happy, but it looks like I need a new starter too.  If this keeps up I'll have a whole new truck soon!

Def

Sent from my MB860 using Tapatalk 2

[derekmac]

As long as you always park on a hill you won't need that new starter ;D

Sent from my Galaxy Nexus using Tapatalk 2

[Grant Lamontagne]

Yes, although sadly I didn't park on a hill this time, I parked in the yard.   

Ah well, I think I'll leave the starter for the mechanic next week rather than do it myself since he'll have it on the hoist for the welding anyway.  So much for trying to get ahead!

Def

[jzmtl]

Bah, push start it, that's like a free gym membership. 

The starter is literally a two bolt job, very easy to access and you can probably change it under 10 minutes.