battery issues

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KamalEK9
Posts: 12
Joined: Thu May 24, 2007 5:13 pm
Location: Oman

battery issues

Post by KamalEK9 »

Hey guys,
i have an electrical issue after relocating my battery in the trunk on my EK. my alternator was bought new in 2005 and used the car for 1 year then i had to garage her for years after the engine blew. so in 2012 i started rebuilding the engine and relocated the battery to the trunk so i can install the T1 catch can. here is how i routed the battery cables:

1) battery + to starter using 2gauge cable
2) starter to fusebox using 8gauge cable
3) alternator charge + cable was left stock that goes to the stock fusebox
4) battery - cable to the rear seat belt bolt using 2gauge cable
5) TB and valve cover grounded using a JDM ground kit that doesnt state the gauge size, but it looks like 6gauge
6) transmission and engine block grounded using 4gauge cable

* note:
all body paint is sanded to ensure metal to metal contact

Issue:
when i start the engine cold i get 14.1-14.3v on idle during enrichment and even when engine has reached working temp. i drive the car around and the voltage is fine. once i park the car somewhere and leave the car idle for for 5-10mins, the afr suddenly goes rich and notice the battery voltage has dropped to 13-13.4v. now i'm running two fuel pumps inline and i can notice fuel pressure drop when voltage drops. by the way both fuel pumps are running off a relay that is connected to the fusebox where alternator charge is found.

questions:
1-what should i check or do?
2- should i replace the alternator even though i bought it brand new in 2005 (has only 14k miles on it)....i have the alternator always on as i'm using hondata (both alternator control and ELD is disabled)...is this how short the alternator life when working full power?
3- should i replace the stock alternator cable with an 8gauge cable?
4- which point of the car does the hondata monitor the battery voltage? is it at the alternator or at the ecu?
Last edited by KamalEK9 on Sat Apr 06, 2013 9:48 am, edited 1 time in total.
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Re: battery issues

Post by Hondata »

The ECU monitors the voltage at the ECU.

The obvious solution is not to relocate the battery (as we do not recommend doing so), but you're probably not looking for that as an answer.

I doubt it is the alternator. What the problem usually is excessive resistance on either the ground side or charge side of the system. And by excessive, I mean anything over 0.01 ohms, which is far less that a multimeter will register.

The base problem is that the alternator regulates the voltage based on the voltage at the alternator. There is always going to be a voltage drop from the alternator to the battery (on both sides). If you do some calculations for that voltage drop, there are several factors - wire resistance, wire length and current flow. On a system with 30 feet of 4ga wire (15 feet ground + 15 feet charge) then the wire resistance is only about 0.007 ohms. If with your multiple pumps the cars is drawing 35 amps, then the voltage drop is going to be 0.28 volts from the alternator to battery. That's not too bad. The real problem is if you have multiple connections, each will a small resistance. eg alternator to fuse box, fuse box to battery cable with one join = 3 connections each with a 0.01 ohm resistance. Now the voltage drop is more like 1.3 volts - you can see how a small resistance is a big voltage drop at high currents. Additionally, you can see that the voltage drop will vary based on the electrical draw from the car too.

The short answer:
- minimize the length of all wires
- never join a wire
- use crimped and soldered end connectors
- go directly from the alternator to battery
- make sure all connections are clean

Then you need to ask yourself again, what's more important: the location of the catch can or a correctly functioning electrical system.
Hondata
KamalEK9
Posts: 12
Joined: Thu May 24, 2007 5:13 pm
Location: Oman

Re: battery issues

Post by KamalEK9 »

i understand what you are saying and would agree its a cabling problem if the issue was there from the start when the engine started cold, engine warmed up and even during driving. BUT if you read my post carefully i do get 14.1-14.3 on the hondata display and the voltage drops comes afterwards as if something get overworked and cant keep up. i'm assuming its the alternator.....i will do a voltage drop and current flow test to clarify the cabling on my car then move forward to the other components installed on the car.

by the way i checked my battery today with the ignition key off and i see 12.78v which tells me my battery is good! i guess i will perform further tests and update you later this week.
KamalEK9
Posts: 12
Joined: Thu May 24, 2007 5:13 pm
Location: Oman

Re: battery issues

Post by KamalEK9 »

i spend like 3 hours yesterday checking things out. The car cranks right up with no hesitation and i get 14.1-14.3v at idle (cold start). After warm up i was still getting 14.1-14.2v with the engine running for exactly one hour. took here for a 1 hour drive and was still getting 14.1v when i was checking my hondata datalogs. then decided to go back home and parked her in the garage and the battery was getting 14.0-14.1v at idle. kept her idling for 30mins then out of a sudden i noticed the lights flicker when the rad fan comes on and voltage drops to 12.9-13.1v. It seems that the alternator is trying to keep up as i can see the voltage jumping to 13.5 then suddenly ranges between 12.9-13.1v . i checked all wiring and grounds. did a current flow, voltage drop test and it was all good. here are the voltage drops from the source to the battery when earlier that day:

* alternator 14.08v
*fusebox 14.07-14.08v
*trunk battery 14.05v

voltage drop when the issue appears:
* alternator 13v
*fusebox 13-12.9v
*trunk battery 12.85v

checked alternator belt and was clean and tight

FYI when the voltage drops it happens everywhere (at the alternator, fusebox and even battery)

what could be that went bad in that alternator?
Arno
Posts: 46
Joined: Sun Sep 02, 2012 8:41 am
Location: The Netherlands

Re: battery issues

Post by Arno »

KamalEK9 wrote: what could be that went bad in that alternator?
Sounds like the alternator voltage regulator may be dying or it's simply not able anymore to provide the required amps to run the cooling fan for some reason and the voltage drops down to (almost) the battery level. Does the situation improve (when the voltage is running low) if you bring the rpm's to around 3000?

Another option if you can remove the alternator is to take it to a rebuild/refurbish shop so they can run the alternator on a load tester to see if it performs up to spec or not and clean/refurbish it if it doesn't. Usually not a big job for them and the alternator is pretty much 'good as new' after that.

Bye, Arno.
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