Battery Size

[DirtDonk]

I'm curious, is my standard Echlin solenoid limited in it's amp carrying ability - is it a weak link in the circuit if I run 2 gauge in to it and 2 gauge out? It probably would take a series of long cranks to melt it down, right? Thanks, John B

It's only a weak link if it's an inferior, or actually faulty part. But then that does happen a lot these days!
Otherwise no, using larger than normal cable does not add load to the relay's contacts at all. Not unless there was something wrong with your old cables and connections that kept the starter from getting it's full current from the battery in the first place.
It can still become the weak link down the road of course, as things start to go wrong with other components. But not due to larger cables.

The starter, no matter what type it is, only pulls what it needs to crank the engine. So if it pulls for example 100amps under normal circumstances, then whether you have 6ga cable or 2ga cable, the starter relay only sees 100a pass through it. Smaller cables might put more load on it, but I'm not sure how that works. If you had to use an 8ga cable, the cable itself would likely be over-worked, over-heated and in that might cause the relay to work harder. But I'm not really sure. The main sufferer at that point is the cable itself, and not the starter relay I'm thinking.
So no detriment to the relay at this level for using larger cables. Heck, even Ford uses 4ga cables in some applications. Maybe even larger on the diesel trucks with two starting batteries.

You're giving things more headroom by using the larger cables, and giving other components like the starter a boost by not making them work as hard. The larger cables will handle longer and longer cranking without warming up and building up resistance, which would slow down the cranking and put more load on all the other upstream components. They do benefit the starter in that there is no limitation other than it's own, as to what it can pull through the cables from the battery.
If I'm not mistaken, a modern starter is going to use in the range of 75a to 100a to crank a normal V8 engine. An old style would use 120a to 150a typically. And an old tired and failing starter motor, or an engine that has too much ignition timing, or is starting to seize up, could ramp that current up to over 200a just to turn the engine over. At that point everything is taking more current, so it's up to us to make sure it's all capable of handling it.
I could be wrong, but starter relays are probably rated for 250a momentarily. But that's just a guess, as I don't believe I've ever seen a rating. Or if I have I've long since forgotten.

So while the relay/solenoid is "probably" going to be the eventual weak link, if you use a quality one it will probably never fail. But quality is relative these days, and starter relays are among the most failure prone of all the modern replacement parts that we know of.

Craps shoot and luck-of-the-draw, to use gambling terminology.
Maybe Viper or someone can correct any of that info that might be wrong or misleading.

Paul

 

[bcmbcmbcm]

I saw a group 65 there...can anyone confirm what will need to be changed to get this to fit? Stock is 24 if I recall.

 

[Madgyver]

That's the same exact battery I have. Been great for 7 years! I don't remember having to modify the battery tray.

it's a tight fit in the stock tray.

 

[Seventee]

it's a tight fit in the stock tray.

Yes it's tight, and it's also nice to have the reversed posts to keep the + away from the fender.

 

[66CTBronco]

So... Everything in an electrical circuit has resistance: the starter, the cables and connections, the solenoid, and even the battery. And all the resistances add up to limit the current coming from the battery (ohms law says current equals voltage divided by resistance. as the R goes up, the I goes down.) A battery can't push current into a load, it has to be drawn by the load (re: ohms law again.) a 6 gauge cable has almost double the resistance of a 4 gauge cable of the same length. Resistances add up. An older battery has a higher internal resistance which lends to it providing less current to start the truck - hence starters will crank more slowly with older batteries. Two batteries provide more current to the starter because the combined resistance of two batteries in parallel is lower than a single battery - so more current, the starter turns faster. Smaller wires have more resistance to carry the current demanded by the starter and provided by the battery - so not only will they help limit the current going to the starter and make it crank more slowly, they will also get warmer while current is going through them (I-squared R losses which is just power being boiled away in the wire.) Starter solenoids have large copper contacts inside them that over time get pitted from the arcing and sparking going on inside them when they engage, the resistance will increase, and eventually there is a significant voltage drop across the contacts of the solenoid which will limit the current going to the starter and cause it to crank more slowly. Bigger wires never hurt. Better solenoids don't hurt either - it's almost planning for when they age. I'm actually surprised at how fast the starter on my little 170 cranks with only 6 gauge wires. when do you want larger wires? higher compression engines, larger engines, if there's a need to crawl a vehicle using just the starter (clutch failed and need to start it in gear to get it home etc), and of course i like the bragging rights mentioned above. The engines and batteries I work with at work always have huge cables to handle the current. Some of my engines have 350kcmil cables because they'll pull 700-800 amps for a minute and a half while cranking. Others have multiple strings of batteries and multiple 4/0 cables going from the posts to the starter to allow over 1000 amps to engage the starter. Ohms law says that current through a resistance causes a voltage. Well if your battery is at 12.5 volts, and you have enough resistance in the wire, connections, and solenoid to drop your voltage at the starter to 9 volts, then you've lost three volts just in the cables and as a result ohms law again will say that starter will pull less current having 9 volts applied to it than it would if it had 11 or 12 on it, and therefore will crank more slowly. Bigger wires gets more voltage (and therefore allows more current) to get to the starter.
Now that i'm afraid i've bored people i'll hush. will be glad to provide more if you want, but figured this is enough.
c

 

[johnbeck]

Thanks 66CT. What solenoid are you using, and are you using 2 gauge wiring from the battery to the solenoid, to the starter? And 2 gauge from the battery to the engine block somewhere? Thanks, John B

 

[gr8scott]

Been using this one for a couple years, no issues.

https://www.rockauto.com/en/moreinfo.php?pk=386504&jsn=3&jsn=3&jsn=3

 

[904Bronco]

Thanks 66CT. What solenoid are you using, and are you using 2 gauge wiring from the battery to the solenoid, to the starter? And 2 gauge from the battery to the engine block somewhere? Thanks, John B

Yes... I make my own cables. Batt ground goes to the threaded hole on the block on the Pass side. Then engine to frame ground...

Solenoid is from a Ford truck... Not sure of year or application. It had extra long studs on it so I grabbed it

 

[66CTBronco]

Wires and solenoid bone stock original... I thought was 6 gauge I’ll have to actually measure tomorrow to be sure. May be bigger I really don’t know!
C

 

[charlie6976]

My parts person is asking me what group size the battery is for my 1966 bronco 24, 26 or 35 and what size cold cranking amps. Any body got a clue.

Here is a size chart. https://shop.advanceautoparts.com/r/advice/car-maintenance/car-battery-size-chart

Sizes 24 and 34 are about the same. I went with a 34 size.https://www.napaonline.com/en/p/NBE9834
This one from NAPA. The 98 indicates post polarity and location.

Keep in mind your power needs. Is it just for starting or are you running a compressor and/or a winch, cooler, etc. So, at some point, two batteries wood be better than one. "Always" have power to start.

 

[DirtDonk]

Wires and solenoid bone stock original... I thought was 6 gauge I’ll have to actually measure tomorrow to be sure. May be bigger I really don’t know!

I've never actually measured or tested one, but I believe you are correct that 6ga was factory original. Was that way for most vehicles I'd bet.
Some of the really old Ford trucks had pretty big cables, but used a different routing altogether. Battery was up and rearward towards the firewall, and I forget where the relay/solenoid was. But some of their cables were either using really thick outer jackets, or were in fact a heavier gauge.

Pretty sure the Broncos all used 6ga in all positions. The next size smaller is 8ga and that does not look anything like a battery cable in size. And once you're familiar with them it's pretty easy to tell the difference between 4ga and 6ga even though it's not a huge difference. When I replaced my first set I used 4ga and they were larger than stock.

Paul