Measuring A Car battery - Page 1
Forum section: electronics / projects

author: challie2
author_rank: Contributor
timestamp: May 01, 2019, 04:56:28 pm
content: Hi allI hope I find you all at a good time.I need some help for a project that monitors a battery amperage.The idea is too create a display stand that measures the current draw from a car battery through a device I have made, and I want to demonstrate the performance. I plan too use one of those Chinese Digital Ampmeters found on Ebay with a 200Amp shunt, there is not going too be any load or consumer on this circuit i.e a starter motor, so would I require a power resistor to ensure the battery wont go bang? I get the idea of the shunt which is a low resistance path and the Ameter is connected across it in parallel. However would I need a power resistor to put a load on the battery circuit if so what size would I need? 12V Battery 200Amp Draw.This is the Ampmeter I intend on usinghttps://www.ebay.co.uk/itm/DC-200A-Digital-LCD-Ammeter-amp-Meter-Monitor-battery-Charge-Discharge-DC-12V/332659117757?hash=item4d74074ebd:g:wikAAOSwX3FbAq9ZThanksJamie

author: InductorbackEMF
author_rank: Regular Contributor
timestamp: May 01, 2019, 05:37:49 pm
content: Hi,you say there is not gonna be any load on the battery, (open circuit) if so how would you measure the current draw?Also yes you would need a power resistor at 12v you need a .06 ohm resistor to limit the current to 200A a VERY big one indeed at 2.4kw!Alex.

author: InductorbackEMF
author_rank: Regular Contributor
timestamp: May 01, 2019, 05:40:56 pm
content: Quote from: InductorbackEMF on May 01, 2019, 05:37:49 pmTo get the size of the resistor you need use thisDivide the voltage by the current you want to get the resistance.And times the voltage being drop`ed by the current to get the power.

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 01, 2019, 05:48:31 pm
content: Just get a big inverter and a hair dryer. Might not be the cheapest option but it can easily be repurposed.

author: IDEngineer
author_rank: Super Contributor
timestamp: May 01, 2019, 06:45:13 pm
content: Quote from: NiHaoMike on May 01, 2019, 05:48:31 pmGood idea if he needs to pull a lot of amps for his demonstration. An even cheaper and easier approach, if he wants to pull single digit amps, would be a car headlight. Literally designed for 12VDC application, readily available, cheap, nonpolarized, graceful failure mode, and almost zero safety issues.So there you go, OP: Two good ideas, depending upon how many amps you want to draw.

author: Benta
author_rank: Super Contributor
timestamp: May 01, 2019, 06:59:22 pm
content: Headlight lamps are a good idea. They are normally rated at 55 W, giving around 4.5 A per lamp. And they're much cheaper than power resistors.But do you really want to draw 200 A continuously? Disregarding cranking, which only lasts a few seconds, it's way outside the normal operating envelope of a car battery.

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 01, 2019, 07:19:19 pm
content: Quote from: IDEngineer on May 01, 2019, 06:45:13 pmHalogen bulbs sometimes fail in a not so graceful way, hence why desk lamps using them have a glass shield. Yet another idea is an automotive heater, typically on the order of 150W.If he's really after a large load, the absolute cheapest would be a length of scrap wire (chosen for the correct resistance) in a bucket of water.

author: IDEngineer
author_rank: Super Contributor
timestamp: May 01, 2019, 07:58:02 pm
content: Quote from: NiHaoMike on May 01, 2019, 07:19:19 pmI was thinking of standard sealed beam headlights. They're everywhere, new and used.

author: Benta
author_rank: Super Contributor
timestamp: May 01, 2019, 08:10:19 pm
content: Quote from: IDEngineer on May 01, 2019, 07:58:02 pmSeeing that the OP is in the UK, that's pretty much a dead end...Standard H2, H4 and H7 automotive halogen lamps are all over the place and cheapoutside the US.

author: floobydust
author_rank: Super Contributor
timestamp: May 01, 2019, 08:23:06 pm
content: You can't pull 200A for very long before the heat ~2.4kW causes problems and the battery quickly discharges.Look at car battery load testers, these are generally drawing 1/2 battery's CCA rating down to 9.6V for 15 seconds or so. Carbon-pile testers can go to 800A, but again only for 15 seconds.

author: IDEngineer
author_rank: Super Contributor
timestamp: May 01, 2019, 08:42:31 pm
content: Quote from: Benta on May 01, 2019, 08:10:19 pmI did notice he was in the UK, but did not know that sealed beams are unavailable there. Really? There aren't any older cars on the road for which replacements are available? Halogens are generally standalone bulbs that insert into a reflector assembly; when replacement is required, the reflector remains and only the bulb is replaced. How do the British replace a failed sealed beam headlight on an older car?

author: Gyro
author_rank: Super Contributor
timestamp: May 01, 2019, 09:15:01 pm
content: The last time I saw sealed beams was on my Dad's Ford Zodiac back in the '70s. It was pretty old by the time he bought it!P.S. When the dipped beams failed he used to make lead acid powered camping lights with them (main beam filaments), very handy for finding the toilet block in the dark!

author: Benta
author_rank: Super Contributor
timestamp: May 02, 2019, 08:40:32 am
content: Quote from: IDEngineer on May 01, 2019, 08:42:31 pmNobody in Europe has been using sealed beams for decades. In fact, they are not allowed and must be replaced with E-codes. This is always done when someone imports a car from the US, otherwise it will fail inspection.H2, H4 or H7s don't need a reflector for this application, just a socket is enough.

author: BradC
author_rank: Super Contributor
timestamp: May 02, 2019, 01:19:56 pm
content: Quote from: NiHaoMike on May 01, 2019, 07:19:19 pmThat glass is there more for UV than mechanical contact/failure.

author: Gyro
author_rank: Super Contributor
timestamp: May 02, 2019, 02:56:24 pm
content: Yes, they're pretty tough if you don't contaminate the envelope. Check out the shape of the one being used for IR reflow in the video - 2:58, after it's been abused at 16V for a while!https://www.eevblog.com/forum/testgear/use-car-halogen-bulb-as-infrared-desolder-tool/

author: IDEngineer
author_rank: Super Contributor
timestamp: May 02, 2019, 05:13:49 pm
content: Quote from: Benta on May 02, 2019, 08:40:32 amRemarkable. I wonder what the "logic" is behind this edict.Sealed beams are an entire form factor. There's no "socket" to hold a standalone halogen bulb even if the connectors were compatible. If the UK compels you to replace sealed beams with standalone bulbs, there must be a market for some sort of retrofit "body" with the same form factor as the original sealed beam unit. Then the halogen bulb would screw into this body. That's how halogen bulbs are done in the USA... the body is semi-permanent and includes the reflector and lens. The replaceable bulb inserts from the back and has an o-ring to keep the interior of the body clean and dry.How do you replace a full-sized sealed beam body with a standalone halogen bulb, while maintaining alignment and shaping the beam and whatnot?

author: Benta
author_rank: Super Contributor
timestamp: May 02, 2019, 05:37:33 pm
content: Quote from: IDEngineer on May 02, 2019, 05:13:49 pmEasy. In the US, the sealed beam is a replacement part. In Europe, the reflector/glass assembly is part of the car. Only the bulb is replaceable.The reason for banning sealed beams in Europe is their miserable beam pattern and low light output.If you follow US car forums, you'll see that a favorite modification is replacing the sealed beams with E-codes (although not allowed in all states).When replacing sealed beams or Hx bulbs, the headlights should be re-aimed afterwards. No difference there, but the European lamps probably need less or no adjustment (the Hx bulbs are very precise).

author: IDEngineer
author_rank: Super Contributor
timestamp: May 02, 2019, 07:48:56 pm
content: Quote from: Benta on May 02, 2019, 05:37:33 pmYes, that's how it works in the USA too. Older cars with sealed beams replace the entire assembly - bulb, reflector, and lens are one integrated unit with connectors on the back. Newer cars have the reflector and lens as a standalone component, "part of the car" as you put it, and the bulb replaces in the back. That's why I said:QuoteMy question, again, is: How do you replace a sealed beam in the UK with a halogen bulb? To be excruciatingly explicit, when you remove the sealed beam you remove the reflector and lens too. Now you have your nice new fancy LEGALLY COMPELLED halogen bulb, and you screw it into... what? The car doesn't have a reflector nor a lens anymore. Do they also sell aftermarket reflector+lens bodies that match the form factor of the now-missing sealed beam? There are a lot of different form factors for sealed beams, so they'd need a whole lot of aftermarket reflector+lens assemblies to match. Is that how they do it? If not, to what do you attach the halogen bulb when there is no reflector nor lens in the car anymore?QuoteInteresting that they compel replacement even in older cars. I can't think of an equivalent requirement here in the States. Old engines can still drive around just fine, they're not required to install EFI or a new engine or anything. Old products are sort of grandfathered in, you're not punished due to the whims of some recently passed law.QuoteYes, swapping out for halogens or xenon or, more recently, LED's is popular. But not compulsory. You must have operational headlights of course, that's always been true, but the ones that came with the car (which, by definition, were compliant with requirements at the time of production) remain legal forever and you simply maintain them to the original specs or better.

author: Benta
author_rank: Super Contributor
timestamp: May 02, 2019, 08:06:58 pm
content: Quote from: IDEngineer on May 02, 2019, 07:48:56 pmEasy. You install OEM or aftermarket E-code headlamps (reflector, lens etc.) which will then stay in the car in the future. Into those you mount the H2/H4/H7 bulbs. Usually, you don't even need to replace the connector/socket.

author: Gyro
author_rank: Super Contributor
timestamp: May 02, 2019, 09:30:54 pm
content: Quote from: IDEngineer on May 02, 2019, 07:48:56 pmI think you're getting a bit tangled here - we're talking newly manufactured cars - or newly imported cars from the US (of which there are very few). If an EU car was manufactured long enough to have had sealed beam lamps, there is no compulsion to retrofit them with modern replacements - it's the same as airbags or seatbelts, although most owners of such old vehicles would of course want to retrofit seatbelts, mandatory annual safety tests do not require items that were not standard back when they were manufactured.As I said, the last car I had experience of with sealed beams was getting on for 50 years ago, it really is averysmall problem. The US seems very behind in headlamp optics technology, we went through the standard tungsten versions of the Hx bulbs fitted in 'permanent' headlamp assemblies for many years (decades?) before moving to halogen [Edit: actually Halogen for several decades too], HID, and now LED, replacements on more recent vehicles.

author: cs.dk
author_rank: Unknown
timestamp: May 03, 2019, 03:16:27 am
content: Diesel glow-plugs are also cheap power resistors.

author: jmaja
author_rank: Frequent Contributor
timestamp: May 03, 2019, 06:47:00 am
content: Amazing! I had never even heard of a sealed beam light before. My first car was made in 1973 and it had H4 halogens. Some even older cars and motorcycles had changable non-halogen bulbs. I have not known about headlights that must be changed as a complete unit instead of changing just a bulb.Has these ever been used in Europe? Sounds like a stupid idea and I learned today they were compulsory until 1983 in the US. All imported cars had to change from Hx to sealed bea

author: GreyWoolfe
author_rank: Unknown
timestamp: May 03, 2019, 11:22:49 am
content: My 1970 Datsun 510 and 1978 Chevy Nova had sealed beam headlights. Fun to aim to pass inspections. Find a blank wall, park the car about 10 feet away, adjust height of first bulb to about knee level and then adjust 2nd bulb to be even with the first. Never failed for lights.

author: IDEngineer
author_rank: Super Contributor
timestamp: May 03, 2019, 02:54:12 pm
content: Quote from: jmaja on May 03, 2019, 06:47:00 amYes, I thought it was crazy when the USA kept requiring them for a while. Well before 1983 there were better alternatives. I believe for a while they required at least one headlight to be sealed beam, and I recall seeing cars driving along whose headlights were obviously different in color temperature, intensity, etc. Crazy times. That's the "logic" of government regulation for you. Not a whole lot different from requiring perfectly good sealed beams to be swapped out for "something else".

author: HighVoltage
author_rank: Super Contributor
timestamp: May 03, 2019, 04:21:28 pm
content: I have used 24V H7 light bulbs in parallel to drain 100A from a 12V car battery to test a charging system.Using 24V light bulbs on 12V has the benefits: last longer, don't get as hot and not so bright.And the current draw stays pretty stable over time.