DIY: Build your own positive battery cable 9456836 for the 850

[Redneck]

I already have the wire, connectors and battery terminals.

My question was about the length to cut the wires to.

[tryingbe]

I don't feel comfortable giving out my measurement as you may not route the cables as I had done, then you'll need different length.

Best to measure it yourself.

[Redneck]

The reader always takes full responsibility for implementing any advice from internet forums and does it at its own risk.

Is there someone who has the information and would like to share it?

[MrAl]

What troubles me actually, is my alternator output. I can't get more than 13.9V from it measured at the alternator terminals without any accessories on. I rebuilt the alternator myself using correct and genuine Bosch components. I replaced: Both bearings, slip ring and voltage regulator. I did not replace the rectifier and coil. I would hate to have to replace the whole alternator after all the work. To keep the existing alternator, I would need to replace the remaining parts: 1) coil - that means replacing everything again and lots of extra work + cost or 2) only rectifier - not as bad. I wonder if old rectifier may be causing lower Voltage output. Do you guys get over 14V in your old Volvos? Is it just my alternator that is weak? or is it typical in our Volvos? Maybe the ECU in our Volvos, or just in my car tells the Voltage regulator to output lower voltage. My battery is AGM. I wonder if it has anything to do with it. Probably not because the ECU doesn't know what battery I have. I read somewhere that AGM batteries need a bit lower voltage to charge.

Hi,

Yes my 98 v70 is the same way, voltage too low. I am lucky when i get 14.0 volts.

I have read that AGM batteries require slightly higher voltage. On my old Hyundai the battery would never fully charge so i had to charge it with my own house battery charger by cranking the charge voltage up to 14.2 volts.
It all started when the alternator on that car went, and i got a new one online. The previous voltage was at least 14.2 volts but with the new one the voltage was 14.0 max. That did not allow that battery to charge all the way so the resting voltage would start at maybe 12.8v and then work it's way down over about two or three months, then needed another charge with the home charger. You could tell too because the engine would not turn over as fast.
After the home charge it would work like new again.

The Volvo seems to be doing ok although the voltage is still too low as far as i know. I measured other cars like a Mustang 2002 and at Chevy 2002 and they were both about 14.5v when engine was running. I always use a good meter too and know the voltage readings as they compare to a voltage standard with 0.02 percent accuracy that i use to test the calibration of all my 100 meters (ha ha, ok not really 100, but i do have about 15 meters maybe more).

I use a analog meter for the car because it response faster than a digital. In the Hyundai you could see the voltage dip down as you started the car, it would go down to about 11v in summer and about 9 to 10v in winter, but when the battery goes low it will go as low as 8v and sound sluggish. I meant to hook this up in the Volvo too but right now i have it connected to the cigar lighter so i can only take reading before and after the car starts but not during the time when the engine is cranking over. I need to connect it directly to the battery terminals as i did in the Hyundai but did not get to do that yet. I also thought about connecting it to the ODBII connector where the +12v pin is. I like running a separate cable right directly from the battery posts (with inline fuse) and right to the meter though, as that is the best possible measurement for the voltage at any time whether engine off, engine running, or engine starting (cranking over).

The car seemed to do ok during the winter too even with the low voltage, so i will wait and see how it goes this year too. The main criterion seems to be that the voltage when resting over a period of 24 hours should not dip below 12.0v and maybe even 12.5v or so. The Hyundai would work it's way down to 11.6v over time so that was a big problem.

Digital meters are fairly cheap these days so you can get one for 5 dollars USD, but i would not recommend one that cheap and go with a 20 dollar one or above. 40 dollar meters are much better. Even Radio Shack meters 20 dollars and up are not that bad, i have a couple and they test good with DC voltage measurements.

BTW there is a chance that getting a new alternator wont help either. I have read that the Eu makers did not take too well to the change in battery chemistry and insisted that 14.6v would quickly ruin a battery so they did not go up in their alternator voltage. I dont know how true that is though.

I also found a way to trick out my Hyundai alternator to get a higher output voltage.
The voltage regulator has a sense input and if a diode is added in series with the three sense diodes then it thinks the battery voltage is about 0.5v lower than it really is so it cranks up the voltage. That's easy though because the alternator does all the controlling.
In the Volvo, i dont know if the alternator does it or the ECU does the controlling. If the ECU does it then the ECU has to be tricked. Maybe someone here knows if the alternator does it or the ECU does it.
If the ECU does it and the sense wire can be found two Schottky diodes connected in anti parallel would drop the voltage to the ECU by about 0.5v and so it would think the battery was low so it would crank up the voltage by 0.5 volt which would be just enough. The diodes would have to be installed in a place that does not bother the other operations of course, and that might mean modification of the ECU itself.

[Redneck]

Thank you for the write up MrAl. It is comforting to see that I am not alone with less than 14V:)

I use a free digital red colored multi-meter that I got from Harbor Freight. It seems to continuously respond to voltage changes.

I don't believe that my alternator is bad. I rebuilt it myself last year as preventive maintenance with brand new original Bosch parts. That makes it better than anything I can buy rebuilt because I know how well I rebuilt it. I am very meticulous and I understand what I am doing. Unless either the coil or rectifier causes it (these two I did not replace), it must be the ECU. I don't think, I want to try trick the ECU. Other than the voltage, the car's brain is still pretty agile:) age does not get to it. I don't want it to end up in ICU or institution:)

If other people here reported similar voltage in the same Volvo models having new alternators and no issues with wiring resistance, we could conclude that having less than 14V is typical. This would confirm that ECU is limiting the voltage. It would be great to hear from someone who removed their alternator from their car, took it to Auto Zone to bench test the voltage output and then compared the voltage after installing the alternator back in the car.

My battery was dying every 2 days lately so I began investigating the problem. As far as I remember my voltage has always been pretty low, but the battery charged fine until now. This battery was 3.5 yrs. old (seemed too young to die for an AGM). I replaced the battery and so far it hasn't died yet. My alternator voltage however is reduced by about 0.5V at the positive battery terminal. The cable in my positive battery terminal is a bit loose and the terminal gets pretty warm. When I wiggle the cable in the terminal, the voltage fluctuates. These are pretty clear indicators that this connection is loose and causes resistance.

My plan is to fix that terminal connection only for now. This will hopefully reinforce and maximize the electrical contact. Even after I fix the voltage drop, I will not exceed 13.9V at the battery terminals.

Since I panicked and bought a lot of 1/0 wire and terminals, I will make the cables too just in case I need them in the future. I wish someone would be so kind and told me how long they cut their wires, so that I didn't have to take the car apart just to measure it.

[MrAl]

Hi,

Yes it would be nice to hear about some other voltage measurements right at the battery as we did.

You cant follow the cable somehow with a ruler and measure it that way? Like measure two inches, mark it, then measure another 2 inches, etc. I dont know how concealed your cable is though and i never had to do it on this car.
Another idea is to follow it with a string, then cut the string when it reaches the other end, then measure the string, leave a couple inches for good measure. Again i dont know how concealed your cable is though.
If you cut it too long you can always cut it again once it is run, even though you'll waist some wire, but if you cut it too short...yikes...time to buy a new wire and start over.
Hey, why cant you run it before you cut it, then cut it at the battery terminal or thereabouts? That would mean you cant make the cable until you actually need it, but is there any reason you need it right now?
Maybe offer your friendly neighborhood auto parts store $5 to let you examine a ready made cable for that car

[erikv11]

+1. To get the cable length right, just get the bare cable in there, so that it spans the distance you wish it to cover. Figure out the route you will use at the same time. Mark it, cut it, attach the ends, install it. I think it truly is that simple, and there is plenty of leeway for small variation in length. Err on the side of not cutting it too short.

Probably a reason no one is sharing an exact length measurement is because no one built one that way: they figured out how long it needed to be on installation (or assembly) day, then cut it and finished the job. That's how I've done it.

[Redneck]

There is also another cable between battery positive and fuse box. I can't see where it attaches at the fuse box. How to access it to even check for any voltage drop there?

[erikv11]

That's called the B+ cable, it is a very common failure especially on 98 models so has been written about a fair bit. You will have to remove the cover around the fuse box, that is probably enough, but try the search button on that one, you can probably find some pics.

[Redneck]

It is not accessible just by removing the cover of a fuse box in 850.