rationalising battery voltage for misc accessories

Batteries, Chargers, and Battery Management Systems.
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alsmith   100 kW

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rationalising battery voltage for misc accessories

Post by alsmith » Dec 08 2015 1:52am

I'm trying to rationalise batteries a little on my bike- I have Cree lights with 2S generally specced at around (but I've seen some variations around the figures) 7.2/8.4V, and also a 12V alarm and a few misc lights etc. Rather that run different voltages I'd like to rationalise to one (in addition to the motor cattery). 12V things are generally specced for car systems so would probably be something like 12 - 15V, but what can I safely run Cree lights at?
The alarm spec says minimum voltage is 12 but haven't actually tested it yet.
I'd prefer to set it up without any voltage converters if possible but it seems like I'll have to go 4S with Voltage Converters.
I have LiPo's which I'd to use but the operating voltage ranges seem to make them not a convenient choice -

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Has anyone any experience or advice that they can share? What kind of Voltage should the Cree T6/U5 lights be safe to operate on? At the moment it seems like buying new LiFePO4 cells (and probably using a Voltage Converter) is the way to go.

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Re: rationalising battery voltage for misc accessories

Post by amberwolf » Dec 08 2015 2:17am

What I would do is use two DC-DCs: one for the 12-15V stuff, and one for the Crees. Both of them would run off your main pack, rather than a separate battery. Probably it would be lighter and smaller to do that, and probably wouldn't eat significantly into your range.


For an example, this is what I do:

I use various LED lighting that is either automotive/motorcycle types, or other 12-15V DC input. All of that on CrazyBike2 runs off a 15V "wallwart" AC-type power supply that has it's wall prongs wired to the main 14s EIG NMC motor battery, and it's output wired to the lights. There's a switch on the input so I can turn the lights off while charging the bike.

The only things not running off that wallwart are my car headlight and the car horns, because each of those uses a whole lot of current. The horn uses so much current that it causes the rest of the lights to dim and isn't very loud. The headlight, if it's on when I turn on the light power, sometimes prevents the wallwart's SMPS from starting up (this has happened with all of the ones I've tried out so far). So both of these are still running off a 4s EIG NMC pack--but I could do without it, if I needed to.


One other issue is that my compressor to re-air up tires if I have to fix a flat or wahtever, also won't run off the wallwart, and needs the battery to do that. :/


The SB Cruiser does not yet have a single wallwart running the lights, as I haven't run across one as good as the one on CB2, and I might need a better one because on SBC the turn signals are still incandescent, if I was to use the headlight on it too. I do have the rear cargo area LED lighting running off it's own wallwarts, wired to the main motor battery just like on CB2.



I *have* used just a regular DC-DC off the motor battery (traction pack) for a bike, DayGlo Avenger, for it's LED lighting and incandescent turn signals and headlight, but it didnt' run any of it as brightly as it could have, and turn signals were "slow" and caused headlight to dim quite a lot on each blink.


Before I went with the wallwarts running my lights off the main pack, I used to just use a separate lighting battery all the time. DayGlo Avenger was my first experiment with not doing that, and CB2 was run that way for a while but started using hte separate battery for horn and headlight just because of the "little issues" with running them off the same DC-DC/wallwart as the rest of it.

I have some significantly larger "12V" power supplies that I've worked on getting to run from DC instaed of AC, but not had luck yet; when I do I'll finally be able to skip the lighting battery entirely, even for teh compressor. One is an XBOX power supply, but so far can't get past the problem taht it seems to require a negative-going voltage on one pin to trigger things for startup, and it derives that from the AC input...so it wont' start on DC without some additional "help".

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alsmith   100 kW

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Re: rationalising battery voltage for misc accessories

Post by alsmith » Dec 09 2015 5:32am

Thanks for the thoughts. The problem I kept coming back to was the 'low' voltage of Cree lights and the high current they need. It seems to come down to using separate batteries just for them, dumping them in favor of 12V lights, or just put them on 12V and see if/how long they last but the thought of potentially unreliable lights isn't a good one. Looks like the decision is deferred again but I'll have another hunt around the pages of the internet to try and find any experiences- I'm quite sure I've seen something somewhere.

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