Printer Friendly Forum Posts - clean 12v from battery?

Hi, first post here.

I'm relatively new to electronics and I could do with a bit of help with my project. My goal is to install a front and rear facing camera system on my motorcycle, but, I'm a bit worried about plugging the cameras and DVR straight to the motorcycle's electrics. Specifically the high voltage (+14V) when the engine revs up and the potential for surges.

First question; is it OK to plug in my cameras and DVR which run on 12V without regulation or surge suppression to the battery (also 12V)? Ok, not straight to the battery but via a relay switched by the ignition key.

If not, what sort of circuit would I need to regulate the voltage and supress surges?

I did a bit of research and I've designed a circuit around the LT1185 LDO regulator (below). It has a drop out of about 600mV at 2A which should be good for the cams and DVR. Finally, how can I adapt the circuit to deal with surge? If necessary that is.

posted_image

Many Thanks,
Dave

Image didn't upload, didn't read :(

Anyway, uploaded to imageshack;

https://img571.imageshack.us/img571/3857/dsc09770medium.jpg

You are reading way too deep into it. 14 volts is the norm.

i am an idiot wrote:

You are reading way too deep into it. 14 volts is the norm.

I'm aware lead acid batteries are normally around 14V, my worry is the alternator which pushes the voltage up over 14V, closer to 15V. Not only that, what about surges? e.g. the surge from the starter motor?

I forgot to mention in case it's relevant, this stuff will be fitted to a Honda CBF125, a cheap bike.

Ditto.

To clarify, if they are for a 12V automotive or battery system, then they will (should!) handle typical 12V system fluctuations including voltage spikes (typically 100V - 400V). Such designs typically handle up to 16V and down to maybe 8V. (Typical voltages are 14.4V max long term charging voltage; 12.7V full battery; ~11.5V for a 100% discharged battery; and during cranking down to 10V or 9V and maybe 8V for a bad battery.)

If it is for a "regulated 12V" supply, that's different. It may only tolerate say 11.5V - 12.5V.
But a 12V automotive camera etc means the typical 8 or 10V to 15 or 16V variation, plus normal spikes.

oldspark wrote:

...
If it is for a "regulated 12V" supply, that's different. It may only tolerate say 11.5V - 12.5V.
But a 12V automotive camera etc means the typical 8 or 10V to 15 or 16V variation, plus normal spikes.

In that case the camera I've chosen should be ok but the DVR looks like it could be a problem, look up "C-DVR", it doesn't look like it's designed for automotive use.

The C-DVR is the cheapest DVR I could find which can continuously record when it's powered on. DVR's designed for automotive use are too expensive for me, hence, the trouble of stitching together a cheaper alternative.

I'm still waiting for the C-DVR to turn up, when it does, would it be possible to find out if it's good to run without regulation by examining the circuitry?

When you get the DVR, if it comes with a 110 volt wall wart to power it, plug that in and read the voltage getting to the DVR.

i am an idiot wrote:

When you get the DVR, if it comes with a 110 volt wall wart to power it, plug that in and read the voltage getting to the DVR.

It should be 12V, which I neglected to mention in my OP.

Both camera and DVR run on 12V.

When you get the unit, if it has a power supply that plugs into the wall, plug it in and use a meter and read the actual voltage that the supply puts out. It will more than likely be around 16 volts.

I'm not expecting the DVR to arrive any time soon, so to pass the time I'll make some assumptions.

Assuming the power supply is pretty much 12V, would that suggest I'd need a regulated 12V supply?

Now, let's assume I need a regulated 12V supply. Would the circuit in post 2 be ok?

The problem with a 12V regulator is that vehicle systems often dip below 12V (eg, cranking, switching headlights, brake lights, or wipers etc, or idling with other loads), hence the regulator drops out or delivers a lower voltage to the device.

Hence dc-dc converters are used. There are IMO great units available at Current-Logic (eg, here) though I recently heard some of their units have regulation problems, though I suspect that's for more critical applications.

oldspark wrote:

The problem with a 12V regulator is that vehicle systems often dip below 12V (eg, cranking, switching headlights, brake lights, or wipers etc, or idling with other loads), hence the regulator drops out or delivers a lower voltage to the device.

Hence dc-dc converters are used. There are IMO great units available at Current-Logic (eg, here) though I recently heard some of their units have regulation problems, though I suspect that's for more critical applications.

A DC-DC converter looks perfect, the example you linked is on the larger side of what I'm looking for, both physically and in power but I get the idea.This smaller one looks alright, I could stick this in an enclosure with the relay. I might as well order one, they look quite handy even if I don't need one for this project.

Thanks for the help.

Great! You found a smaller & cheaper one, though I was sure they used to have a smaller 12V cased unit for around $15.

I was blown away by their prices, hence IMO to make a robust dc-dc conv, forget it! One day I'll be getting some myself, probably even for "just in case" scenarios.
They are that cheap I reckon if in doubt about a load being "12V", or "vehicle 12V" and hence 9V-16V etc and transient protected, just get a Current-Logic and play safe, and avoid dropouts to boot (pun intended - for PC etc loads).
Plus those dc-dc convs are switchmode (SMPS) and hence far more efficient than linear regulators.

And apart from the one I mentioned, I haven't heard any complaints about them. In fact, quite the opposite (ie, praise.)

And BTW, not that I studied your now deleted pic in detail, but congrats on your research etc - ie, your low dropout regulator an its circuitry.

Do you have any idea of the current requirements of the DVR?

i am an idiot wrote:

Do you have any idea of the current requirements of the DVR?

The power consumption of the DVR isn't in the spec but the power supply is said to supply 1A at 12V. Having used many bundled power supplies from the far east I'm dubious it will actually supply anything close to 12V at 1A. Which, isn't a problem, because obviously I wouldn't be using it on the motorcycle and second I'd be very supprised (and disappointed) if the DVR drew more than 400mA on full load.

In the real world, battery to relay switched via ignition with a 3-5 second delay would be ideal. I think you could get a 3 second delay on relay from an vehicle AC parts distributor.

-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

That depends on what the equipment is.
If it's plugpack etc supplied, it may only have an 11.5V - 12.5V tolerance.
If its designed for automotive 12V, it may handle up to 15.5V or 16V etc plus typical surges, but may not like dips below 12V, 11.5V etc.

Almost every vehicle's battery will drop below 11V during cranking, hence resetting dip-intolerant loads like PCs and uPC controlled equipment.

However direct connection to the battery (via a relay of course) has solved many such resetting/rebooting issues, and sometimes better than a diode with big capacitor does.

Certainly for PC type loads, the dc-dc converter is usually the only solution. And since DVD players incorporate uPCs, the same often applies. (Same for modern HUs etc.)
(Exceptions include 5V devices like tablets & GPS. Even if they have an ancient linear regulator, they should work down to at least 8V. But most use SMPS converters ie, dc-dc converters, and hence should be dip tolerant.)

Peter, note my delay on comment.
Unless m/bikes have a 2nd. non-cranking ignition.

-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Yeah, I did - sorry, but I did not elaborate...

Although the delay means no DVD during the cranking dips & its spikes, the after-voltage might be higher than usual (some alternators output above 14.5V just after cranking if (or when) the alternator is cold), but otherwise the usual ~14.2V.
The load (DVD) still sees ~20% higher voltage than is 12V rating (ie, 14.4V) even if the lower-voltage cranking dips are eliminated using a delayed relay.

Another consideration is how the unit should behave after engine stalls and hot cranking - continue operation, or is a break ok?

Point taken, I was just going for the KISS answer.

-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

It is also the "guaranteed" versus the chancy.

If the dc-dc conv (~$30?) isn't much more than timed relay, IMO play safe. But a 120W dc-dc conv may be >$100.

There is also the UIBI idea - the alternator charge light circuit energises an ordinary relay. In most cases, that means relay energisation AFTER the engine has started.

But otherwise, a DIY timer may only add a few $ to the relay price, hence be worth a try. (I'm not au fait with those fancy relays - the 520t's or whatever...)
Alas I often overlook such timer-delayed solutions, more so because I am unaware of those fancy relays and their prices and availability.
It is certainly a good suggestion that may fit the bill.

As usual, it depends on what the load tolerates, and what the user wants (ie, occasional reboots ok, or guaranteed ride thru).

Peter, a DEI 528t goes for about US$15-20 on fleabay.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

That's pretty good. Even though I am Mr Cheapskate DIY using common & standard parts, I'd go for that.
Why other taking the time and effort to build a circuit.
And the DEI 528t has settable 0-90sec delay and polarity options...

Put it this way, if I ever see some going cheap, I'm likely to buy a few. (Unless I build my "standard" PIC-08M2 relay etc, but the USA will have gone metric by then...)

Let me know if I forget to include delay solutions in the future! (As if my replies aren't long enough already!)

It's just occurred to me that this whole thread is pointless.
I'm just starting a project to install GPS linked cameras with SD card storage in London taxis, two cameras can be separated, look up Novus vehicle cameras, about 2 x 1/2 x 4" draws about 30 mamp.

-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

It may well be.
But as I recall, the cameras are plugging in to a DVR and there is no info about whether the DVR can power the cameras etc.
AND the issue is presented as one of voltage tolerance of the loads (DVR or cameras) as distinct from power requirements.

(The string is twice the length from its center to an end.)

All done! Took a while for everything to arrive from the far east.

I decided to use the DC-DC module in the end, I had nothing to lose bar a few coins. I haven't got a scope but my DMM tells me a steady 12.0V is coming out of the DC-DC convertor even with the starter motor cranking.

The camera according to the specs can take an input voltage of 8-16V and draws that power separately to the device the video signal is sent to. Despite this I hooked it up to the DC-DC module for good measure.

I'm still unsure of the input voltage range the DVR can take, I've measured the AC adapter that it came with to have a no-load voltage of 12.4V which falls to 12.2V when powering the DVR. Better to be safe than sorry I suppose, especially if there's some camera footage that I really don't want to lose.

All in all the project set me back £45, a success in my book because an equivalent off-the-shelf option would be at least £100.

Anyway, thanks for the help!

I'm glad is was a success.
I especially like the £55 saving - you could have two for one or maybe even 3 depending on the converter capability. (Maybe a rearward facing camera, and one for your GPS or speedo to prove you ~~were~~ weren't speeding.)
But that's usually the advantage of DIY - cheaper cost. Also that you may have more freedom in sourcing parts, carrying spares, or a system that better suits you.

The camera(s) could be moved off the converter since it seems designed for car 12V systems, but it's fine on the converter. Besides, the converter should ensure it works during voltage dips (assuming the converter can operate at a lower voltage then than camera) and it provides extra protection against spikes etc.
Alas for the DVR, its PSU doesn't say much about what what the DVR itself will tolerate. But you played safe. I can only reiterate that there is a big difference between a 12 volt device and an "automotive 12V" device. (If it comes standard with a cig-socket power lead, then it is (or should be!!) automotive 12V compatible.)

FYI - some convertors can be noisy. They use high-frequency switching that can interfere with radio & video etc (the M2 & M4 ATX supplies are renowned for that). But they shouldn't - they should be fully metal enclosed and have appropriate input & output filtering.

I'm glad the12volt could assist.
Maybe let us know if the setup saves you conviction or claims in the future, or if our - I mean your - video hits "World's Worst Drivers" or youtube etc.