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Automotive/1997 Ford Explorer Charging system

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Expert: - 3/1/2009


Question
Hi,
I own a 97 ford explorer, and 3 days ago I noticed the battery gage goes up and down when I have the AC/Heat blower on or any other eletrical component on.
I bought a brand new battery and new terminals and put it in and it still does it, so I bought a re-built alternator and installed it and it still does, I don't what else to check and how to go about doing this, do you have any advise for me?

Thanks.

Answer
Not having the details on the battery-monitoring system that may be used in the 97 Explorer, I shall use the opportunity to provide a general answer that might be useful to anyone contemplating adding battery-voltage monitoring to a vehicle ...

Ideally, battery voltage gauges will be wired directly to the battery terminals, in order to an accurate reading of battery voltage right at the battery, regardless of voltage drop due to current flow in the main bus or feeders that connect to it.  One can expect the battery voltage to drop to some extent when there is a load on it, as the battery itself does have internal resistance, but this is very small so the battery voltage should not drop more than a few hundred millivolts for most loads, and maybe two or more volts while cranking the starting motor.

If the battery meter was installed as an aftermarket item, it is possible that an uninformed installer may have instead wired it to some convenient terminal within the instrument or accessories clusters, in which case the meter's reading would be much influenced by line voltage drop at that point as loads are added or taken off.

If your gauge has been wired in the latter manner, you should disconnect it from that non-stiff point of connection and reconnect it via a dedicated run of 16awg or larger wire, on both positive and negative sides, to the battery, connecting the negative run directly to the battery negative terminal, and the positive run via the contacts of a small control relay, contact rating 10A or more, with a 12-14VDC coil.  The coil may be energised via a tap from your key-enabled accessory system, so that the meter is energised only when the key is in accessory or run.

If the meter is a simple very-low burden voltmeter type, ie: a 1mA full-scale-deflection (FSD) meter movement and a 15k-ohm or so multiplier resistor, you need not bother with the relay; the meter can monitor the battery voltage on a continuous basis, within reason - meaning that a winter-stored vehicle should be equipped with an automatic charger to keep the battery up.

Hope this helps ... EGK

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Ernest (Ernie) Kenward

Expertise

The challenges I most enjoy are thoughtful technical questions of a trouble-shooting nature in both electrical, power electronic and mechanical systems, mainly automotive but also machine control and small-machine PLC applications. Please note, however, that I am NOT a walking shop manual! I DO, however, make it a point to have those manuals and other service literature for those vehicles I DO own, and highly recommend that anyone serious about maintenance or modification of their vehicles do the same; MOST of your answers WILL be found there. For that matter, I do NOT go out of my way to acquire shop manuals for any vehicle I do NOT own! That being the case, any general query to me along the lines of "What is the meaning of this code read from the ECU of my 2015 XYZ?" or "Where is the fuse for the windshield washer pump found?" (try your car's electrical distribution panel for a start!) will not go far. What I do offer is a pretty good collection of literature, insights and hands-on experience with 1950s to 1980's Ford products (plus a developing database of information and practice with the Mercedes diesel cars), along with an engineering perspective and the ability to design and implement custom control, electrical and mechanical subsystems for vehicles. For that reason, I am happy to make my thoughts and efforts available to those who are of like mind and/or are seriously making a point of learning about their vehicles. Use the Opportunity to Learn!

Experience

A key skill in my work and hobby pursuits both is STRATEGIC TROUBLESHOOTING. I am a senior instructor in Electrical Engineering Technology at a leading Canadian polytechnic, my areas being Electrical Power and Industrial Control, electrical and electronics design and manufacturing, and AutoCAD and related CAD/CAE software - plus equipment problem-solving and new equipment design and prototyping. Hobby-wise, I have 30-plus years of experience in auto restoration, mostly in electrical and mechanical systems. Ongoing projects include a 1959 Edsel Corsair, my 1978 Ford E250 class-B motorhome conversion, and the care and upkeep of my Mercedes 300CD. My vehicles become engineering test beds for electrical and mechanical upgrades as ideas present themselves. This includes the design and production of circuit boards to restore or enhance features for which no OEM replacement parts are obtainable, or where better specifications or reliability can be had via newer concepts. Regarding the E250 RV conversion, I designed and continue to revise a custom power distribution system, managed by a Programmable Controller (PLC); this has made most revisions as easy as uploading new firmware as I develop it. The "mini" PLC is a powerful device for custom automotive control systems. One good example (there are many) would be the Moeller "Easy Relay"; these offer a wealth of control, monitoring and variable-and-status display options for such projects. A good example project which has worked well is that one for my RV noted above, which has been on the job - revised in firmware only - for a decade now. It is a load management and charging control system to avoid the sulfation-induced early failure that often befalls deep-cycle batteries used in RV power applications. The battery installed in 2003 lasted long enough to more tnan pay for the PLC that contributed to its longer life ... and the PLC will be there for the next battery as well!

Organizations
IEEE - senior member ... past WCC Student Activities; SME - senior member ... past chair, greater Vancouver chapter chair 318; Edsel Owners' Club - have served in various capacities on chapter executive during seventies; have been Power and Driveline resource on the Edsel Owners' Club "E-team" for more than a decade.

Education/Credentials
Graduate of UBC

Awards and Honors
Certificates of appreciation from IEEE and SME for work in student and chapter activities

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