tgaffner

Obviously i would make it a nicer setup than just bolting the negative terminal to the area in question, but I would like to know if this set-up would work.

It seems like an ideal location seeing as how 1 of the 3 leads goes right to it anyway. Also, it wouldnt require lengthening of the other 2 grounds.

Rotaman

tgaffner, personally I think you should go back and read some of the posts that have been put up on previous pages of this topic. That cross member is just tack welded into position, so is not an idea place to use for your main battery connection. It would be ok as a secondary position, but thats all.

tgaffner

Okay, thanks

tgaffner

Alright so i cut open the oem harness back to a certain point to be able to not only identify every wire, but also be able to work with them.

So these wires were incorporated into the stock battery harness in one way or another and need to be dealt with:

Electronic Power Steering +
Starter Motor +
Fuse Box +
Alternator +

Radiator Fan -
Motor -
Chassis -

As far as all the positives, I plan on running 2awg from the battery in the trunk, to a distribution point under the hood. A foot off the battery there will be a fused breaker either 120 or 150 amp (Have not found one that I liked yet.)

I am going to mount my distribution box/panel onto the crossmember under the battery box. It will be insulated from the member so no worries there. Im using this location because it will allow me to connect the factory + wires to each other with out having to extend anything. I have not found the exact distribution block that I want yet, but it will be fused and a 3-way design.

Battery--> EPS
................Starter
................Fuse Box

Now factory has the starter and fuse box leads crimped to the same terminal, but I need to seperate the two depending on which distributer style I go with. Now that leaves 1 positive lead untouched, which is the Alt. Seeing as how it goes straight to the fuse box as it is, I see no need to change it. Am I correct in assuming this?

That handles the + side of things. As for the -'s, there are really only 2. Fan and a Motor ground. There are three, but the chassis is once again crimped in the same terminal as the motor ground. So if one where to ground out the motor, it would then eliminate the need for chassis (it wouldnt be doing anything.)

Im thinking that if I grounded out the Motor - and the fan - to the frame just below the fuse box, that it would suffice. Both wires will reach this location without modification.

I will also ground out the battery in the trunk to a stud that i weld on by the rear seat area. I will also run another motor ground. Probably from a water pump bolt seeing as how they are right there, going to the frame under the fuse box.

Does this seem like a good set-up? I have read every page in this thread and it seems like the way to go

Rotaman

tgaffner, Try posting up some photos if you can, that will help us to see what you are trying to achieve, and make it easier to give advice/help.
Most of the distribution blocks that I looked at when I was relocating my battery into the boot, were poor quality, so I ended up making my own out of solid brass plate. Take a look at some of the photos I posted in previous posts.
Don't use a water pump bolt as a earth, use the engine block. There's a good earth point down the bottom of the centre iron below the dip stick. From memory its the factory earth point anyway. If you want to run an extra earth up to the earth point on the cross beam that you have indicated you were going to use anyway, that would be ok. Just make sure you link the earths to one good point.

Have fun

Rotaman

tgaffner

This is the grounding spot that I was thinking of using. Its the blue painters tap under the fuse box.

The ground you were talking about near the dipstick, is the factory ground that goes to the battery. It also has a jumper wire that goes the the cross beam under the battery and intake tray.

I was going to take the factory block ground (dipstick) and bolt it to the marked location. I was just going to cut off the jumper wire thats crimped to that ground wire.

Rotaman

I would think that would be a good spot, straight onto the chassis rail.

hufflepuff

i thought the starter, in OEM configuration, is only grounded through the body and the transmission case? And then aren't you still relying on the OEM engine-to-chassis grounds to return that current to the OEM battery negative?



How would you "direct ground" the starter?

hufflepuff

https://www.summitracing.com/parts/sum-900271/overview/


would this work well as a "fuse" / disconnect for when the car is sitting for long periods with a small-ish battery, or are there better options?

NotAPreppie

I used the 250A version of one that for a while.

I had three concerns:

1. It's made of plastic and the mounting holes break off very easily.
2. The terminal posts are small and most cable terminals for 1/0 AWG and larger cables are too large to comfortably fit. It can be done but it's not ideal.
3. It didn't trip when I forgot to disconnect the battery before doing work and accidentally shorted the power wire on the starter to the chassis.

hufflepuff

Dang, what did you end up switching to? Thanks for that feedback.

hufflepuff

There's a lot of discussion of cutting into the OEM wiring and making junction boxes. Is there any problem with bolting your large gauge battery positive lead directly to the OEM positive connection as shown in this article?


2005 Mazda RX-8 - Quicky Tech - Project RX-8 - Modified Magazine

NotAPreppie

I ended up going with a 250A fuse. It's doesn't fix the last problem and it won't act as an easy switch but it feels much more solid and secure.
http://a.co/iRqjZo4

I built a small bracket out of square tube to mount in the OE battery location. I mounted positive and negative battery terminals there and re-used the OE connections. I ran into a problem with not being able to clean the oxidation up enough to make a good connection with the OE terminals. Measured 100 ohms between battery + and starter. Ended up connecting the battery directly to the starter and then using the OE harness to go from the starter to my bracket.

hufflepuff

I used a dremel with a tiny wire wheel to blast the oxidation off my OEM positive terminal. But i'll still do some voltage drop or impedance measurements as you suggest.


My current thought on a fuse / disconnect breaker is a Bussman CB285-150. It's a good brand and 150A is just a little higher than the 120A RX-8 main fuse. It will also let me conveniently disconnect so my small li-ion battery doesn't overdischarge.

wfd1

Please excuse me for some stupid questions. Being dumb at electrical stuff really sucks.
I am an RX-8 owner from China (Just got it last year, probably I'm the 5th owner). Just registered here! YEEAHH!
So, I was originally trying to relocate/remount a smaller battery to where the washer fluid tank is and fabricate an integrated tank for washer fluid/2t oil/battery bracket for this application and found that there won't be enough space for liquids and battery. So I came to look at the trunk relocation solution here.

Internet connection from mainland China to this board somehow sucks so I had hard time trying to open those thumbnails (and somehow I cannot upload pictures too..)
And now I have some problems that needs to be clarified by all the RX-8 gurus here.
1. How and where does the wire go through front firewall into the passenger space and into the trunk? Does the process include any kind of drilling or cutting?
2. Do I have to run ground wire back to the engine bay? (2 wires going through cabin space)
3. If 2 is Unnecessary, Where do I ground the negative terminal. And in this case Do I have to enhance grounding in engine bay since things are not routed to battery negative then.

Thank you guys.

Andrew5190

iTrader: (1)

1. Literally the 11th, 12th, and 13th posts in this thread
2. I personally did not, but others did.
3. I grounded to one of the strut tower nuts behind the "wall carpet" in the trunk. I also did nothing to engine bay grounding, but I also added a jumper post to the front. See this post: https://www.rx8club.com/series-i-do-...7/#post4382960

topolittle

Sorry for reviving this old thread but I think it's a good thing to put all the battery relocation information and questions in the same thread.

I want to relocate my battery, so here is what I am planning to do:
- Optima Yellow Top D35 in the the trunk (passenger side, just behind the back seat).
- Batt+: 2 AWG OFC from the trunk to the front
- Batt-: Short 2 AWG cable to the chassis in the trunk
- Distribution block in the trunk (150A to the front, 50A to the aftermarket audio amp in the trunk)
- Distribution block in the front (starter unfused, fuse box unfused since there is one in the box, 60A for the EPS)

About the alternator wire, I am not sure how to wire it. Since the alternator output a pulsed DC and the battery act as a capacitor to filter it, should it be better to route the alternator wire from the front to the trunk using 4 AWG and connect it to the battery directly? This way it should be less noisy. Or maybe it's not a concern and I am just worried for nothing. What is your thought about that?

ciprianrx8

Wrong. You don't need to tap on the original location of the positive battery lead. Tap into the big starter bolt - that's your biggest current drain with the engine off.

See above. Trim the original harness so that you retain the EPS fuse and alternator wiring. From the starter you already have a wire going to these 2, trim excess and tuck away somewhere nice.

See above again. The alt. does NOT output a pulsed DC - the waveform is a bit irregular due to RPM and field coil duty cycle. The battery takes care of that, albeit now it sits further back and as such behaves like a poor capacitor not doing much filtering. The car won't complain though. Tie alt. output close to EPS(that's your biggest current drain with engine on) and then go towards the starter bolt which is then tied to battery +.

topolittle

Thank you ciprianrx8. I it will be much simpler to do as you said.

I decided to go with the Optima D51 YellowTop instead of the D35 to save some weight. I Don't use the car during winter and it's mostly for the track, so I don't need a big battery.

About the gauge size for the battery wire that goes from the trunk to the starter, is 2 Gauge OFC is enough or should I go with bigger gauge (e.g.: 1 or 1/0) ? I don't want to route the cable under the car. I am planning to route the cable under the door sill on the passenger side, and I have read that some have done it on this forum using a 2 gauge cable. However, I don't know if a 1 or 1/0 will fit.

A bigger gauge weight more and is more difficult to work with. If a 2 gauge is enough and a bigger gauge is not required, I will stick with the 2 gauge. So, is a 2 gauge enough for this application?

Rotaman

Maybe you should go back a few years on this topic and read a bit more of the topic. I think you will find all you are looking for, for a rear mounted battery. At least the info will help you out.

TeamRX8

iTrader: (25)

spoon feeding noobs is no different than feeding an alligator or crocodile; eventually it will become bold enough to eat somebody’s pet or kid. :truestory:

it won’t kill you to read the thread buddy, you might actually learn something worthy of being proud to know and accomplish all on your own. Obviously you’re not blind. Or do you think it’s ok to beg for food simply because you can’t be bothered with finding and keeping a job? Because we’ll help anyone who honestly needs help, but also tell you point blank that lazy people deserve to starve.

The entire point of a DIY area filled with DIY threads on numerous topics is to provide others with what they need to know. There’s no excuse to be asking a question unless the answer isn’t already posted or you need a clarification on some point that isn’t clear.
.

topolittle

Dear TeamRX8, thank for your taking time to answer my question. Unfortunately your answer is useless for me since Rotaman already given me pretty much the same answer as your, except with better delicacy.

According to ChatGPT, you were both right. The answer I was looking for is indeed somewhere in this thread.
From ChatGPT, about the fitting: "According to the forum thread you provided, it seems that fitting a 2-gauge wire under the passenger door sill is more feasible than fitting a 1/0 gauge wire. Some users have reported success with using a 2-gauge wire for battery relocation, and it may be easier to route and install than a thicker wire."

And for the gauge to use:"According to the forum thread you provided, using a 2-gauge wire to route the battery positive to the starter is sufficient"

I hope that my answer will help others like me who don't take time to read 300+ post.

topolittle

I have completed my battery relocation and I would like to contribute to the thread. So here is what I have done:

• I used a 1 gauge OFC SAE-J1127 cable and I routed it under the passenger door sill. It fits really well but I had to remove the 3 white plastic boxes that was around the existing cable harness. I drilled the firewall behind the washer fluid reservoir.
• I used a battery box from Eddie Motorsports (P/N MS374-71). I secured the box to the floor with 4 rivnuts and 4 bolts. I removed the sound proofing membrane and installed VHB double side tape before screwing the battery box.
• I put a 200A fuse in a custom 3D printed box, above the battery. The box has room for another fuse, In case I want to add an audio amplifier in the future.
• In the front, I installed a custom 3D printed distribution block with a pass through for the starter, a 60A for the EPS and a 150A for for the fuse box. (I know there is already a 120A fuse in the fusebox).
• For the ground, in the trunk it's connected to the body at the base of the strut AND to the diagonal reinforcement behind the rear seat. In the front, all the ground are connected in the center, above the fans.

I know it would have been better to route the battery wire directly to the starter as others have suggested, but I didn't want to struggle with a big wires under the car, so the battery cable goes directly to the distribution block. The started is connected with the stock cable.

I also replaced my starter with the upgraded 2KW one. The difference is huge.


​​​​​Here is some pictures







​​​​

Dimension23

I know this thread is really old but have you ever had issues with this setup? I’m thinking of doing this to my 8 soon along with an AEM intake to improve cooling.