Car battery voltage drop - Page 1
Forum section: electronics / beginners

author: dontfeelcold
author_rank: Newbie
timestamp: February 24, 2015, 10:13:24 am
content: I am in the process of setting up sensors in my car to monitor the engine so that I can tune it.One of the sensors is a thermocouple. The thermocouple signal gets boosted by an amplifier that needs 14.5v to 32v to get the maximum reading from the thermocouple. The other is an oxygen sensor whose controller runs from 10.5v to 19.5v. The combined maximum current draw is 3020ma but I would like some more headroom.My car while idling runs at 14.8v but it drops substantially for a split second when another component of the car is activated (hydraulically controlled 4WD). This keeps happening from time to time as the car needs to keep pressure in the 4WD hydraulics.So I will need something that can give a consistent output voltage that satisfies both devices despite what happens on the input.Is there a type of circuit that will do this? I am looking to do the circuit myself but need some help to understand what kind of circuit I will need.

author: ProBang2
author_rank: Frequent Contributor
timestamp: February 24, 2015, 10:48:11 am
content: Hello.No circuit necessary. Get a "Booster-Cap" for car-HiFi. And a diode.The delivered voltage will be: 14,8V - Voltage drop of the diode.This level will easy hold by the Cap while voltage drops. Even with a current of 3 Amps or more.The diode is necessary to avoid the reverse loading of the battery from the Cap.Greetings,HartmutP.S.: The amp with min voltage of 14.5 V is for sure not a dedicated device for using in a car.Rethink this part, please.

author: ccayser
author_rank: Contributor
timestamp: February 24, 2015, 11:02:49 am
content: You also might consider using automatic buck boost converter. They are fairly cheap and should do the trick. They are available on ebay.

author: mjrandle
author_rank: Contributor
timestamp: February 24, 2015, 11:29:39 am
content: A large capacitor will work, but care needs to be taken to ensure it is discharged before working on vehicle. The third option would be to run a dual battery system, either two identical batteries with a battery separator contactor or a significantly smaller auxiliary battery powered through a diode or float charger. With the former, wire sensors on auxiliary battery and starter / hydraulic pump on main battery. With the latter, the small battery just provides voltage during the brief voltage dips.But to meet above voltage range, you will still need a boost converter.Cheers,Mike

author: dontfeelcold
author_rank: Newbie
timestamp: February 24, 2015, 11:30:56 am
content: Thanks for the help so far.The oxygen sensor pulls max 3amps and operates from 10.5v to 19.5v while the egt probes pull 10ma each and I will be running 2.The oxygen sensor is design for automotive use.

author: dontfeelcold
author_rank: Newbie
timestamp: February 24, 2015, 11:38:36 am
content: Found something capable on ebay, thanks again.

author: dontfeelcold
author_rank: Newbie
timestamp: February 26, 2015, 07:20:38 am
content: Since looking into things further, I am unsure if running a separate battery charged by the alternator but isolated to the rest of the car will smooth out the voltage drop when the hydraulics momentarily run. My understanding is that the the alternator runs the car when it's running, not the battery, so a second battery will still drop it's voltage but only down to its resting voltage.Will a boost converter be able to maintain a stable output despite the 2-3v drop? Do I need to be more specific on the actual voltage drop and the time it is low?

author: ccayser
author_rank: Contributor
timestamp: February 26, 2015, 10:07:45 am
content: Usually the car battery is charged all the time when the engine is running. I am not quite sure, maybe newer cars have some magic in them so they detect when battery is full and they cut out the battery from the circuit and car runs solely on alternator.The buck-boos converter gives you desired output whether the input voltage is lower than desired output voltage or lower.

author: tautech
author_rank: Super Contributor
timestamp: February 26, 2015, 10:19:10 am
content: 2 simple options that may be worth considering and/or experimenting with.Another similar sized battery in parallel with the main battery to help buffer the current draw.That should reduce the voltage drop.Replace the battery with a larger more capable one.

author: Seekonk
author_rank: Super Contributor
timestamp: February 26, 2015, 11:16:39 am
content: All your sensors easily handle a higher voltage so just use a small boost converter or multiple ones. 3A seems like a lot for sensors. I have used about a dozen of these at my camp to boost voltage. Just set it to 16V and suggest you place an additional 4700uf or higher on the output.http://www.ebay.com/itm/150W-DC-DC-Boost-Converter-10-32V-to-12-35V-6A-Step-Up-Adjustable-Power-Module/171219013561?_trksid=p2060778.c100276.m3476&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D20140725133649%26meid%3D216c3e7fe12c47c09966db61cbc21c0e%26pid%3D100276%26rk%3D2%26rkt%3D4%26sd%3D261201225563

author: Mechanical Menace
author_rank: Super Contributor
timestamp: February 26, 2015, 05:42:08 pm
content: Why not just use a temp sender and lambda sensor from a scrap car? Depending on the age of the car they come off of they will either run in the voltage range a car does or at 5v.

author: eejake52
author_rank: Contributor
timestamp: February 26, 2015, 08:16:17 pm
content: You might want to consider using the OnBoard Diagnostics (OBD) interface, which has been present on most cars for the last 20 years. More info here:http://en.wikipedia.org/wiki/On-board_diagnosticsJake