Ask HN: Fellow dads, I need help with a baby monitor (electronics question) | Hacker News Reader

Ask HN: Fellow dads, I need help with a baby monitor (electronics question)

4 pointsherodoturtle7 comments

Fellow dads,

Our baby monitor is rated for 6 volts, and comes with an appropriate adaptor.

In my part of the world, electricity supply is unreliable (we get cut off for a couple hours at a time).

As such, we've gotten used to using these little Lithium Ion battery kits to power small appliances (such as the WiFi router) - they work great!

I have a spare little battery kit as described above, and it has two voltage output options, namely 5 volts and 7 volts (I can select between the two with a switch).

The baby monitor is rated for 6 volts, so I'm wondering - can I use this battery kit? And if so, should I switch it to 5 volts or to 7 volts?

Any significant risks at such low voltages given that it won't be exactly 6 volts?

My knowledge of electronics is minimal, so apologies in advance if this is an ignorant question ^_^

Thanks a bunch!

View on HN

We need some more info to get a clear picture. But I am going to assume the following: your baby monitor takes a 6 Volt DC input at around 0.4 to 1 Amps (like usual Vtech models). which means the power it consumes is from 3 Watts to 6 Watts.

I would definitely not plug in the 7 Volt adapter as if the current is too high it might damage the circuit.

Whether the 5 volt source can be used would depend on the current. If its a standard USB 5 Volt output most modern day ones are 2 Amps, which would mean the power output is 10 Watts, which may be too much for the circuit. If its 5 Volt, 1 Amp output then it might be okay to connect and test out without damage to the circuit.

What I would recommend is a DC to DC regulator or converter. Something like the following from amazon that would take an input of the 5 Volts and give you 6 Volts out. Make sure to test the output voltage and current with a multimeter before plugging into the monitor.

DC to DC buck converter from amazon: https://a.co/d/9jiA7Ls

Well, first of all, nothing is impossible. But, you are likely ok. However, the risk with the 5 volt is more likely that it just won't power up and function at all, whereas the risk with the 7 volt is more likely that it could blow something (damage the electronics).

There is also a current rating, but it seems likely that the monitor would not have a huge requirement for current. IANABME (I am not a baby monitor engineer).

So, if getting a 6 volt source is not an option, I would try the 5 volt first, and if it doesn't work then try the 7 volt, with the knowledge that there is a small chance it could break the monitor. But (in the USA anyway) anything made for 6 volts would normally be able to handle 7 volts. Normally.

There's not much risk trying it at 5V. Low voltage may result in poor perfomance, but probably won't result in damage; although it's not technically impossible.

Higher voltage may result in damage, but if it won't run at 5v, or it runs poorly, and the baby monitor wasn't too expensive or hard to replace, I'd personally take the chance at 7v. But I'm just some internet person. You're unlikely to have an exciting failure at 15% over spec voltage if it normally runs from a wall wart; those things often don't have great voltage regulation, especially if they're runnig from iffy utility service anyway.

Does the baby monitor accept alkaline batteries? If so, it will work on 5V. That’s equivalent to 1.25V/cell, well within the next expected voltage range of a typical partly-discharged alkaline battery.

Good insight here IMO

I bet it won't make much difference whether you select 5v or 7v. But I'd rather under volt something than over volt. So I'd see if it works at 5v.

It's probably unlikely but an over voltage could result in some component going through its breakdown voltage level (although I think 7v rather than 6v makes this unlikely). And from Ohm's law (V=IR) current and voltage are proportional and so more volts and you'll get more current and that could burn something up.

It might be fine with either 5 or 7 volts, but if you’re worried, search online for 12v to 6v DC converters. You could put two of the battery packs in parallel (one set to 5v, one set to 7v) to get 12v input. Then connect the 6v output of the converter to the baby monitor. There are probably other converter options that would work with just one 5 or 7 volt input but 12 to 6 is very common.

Reply on news.ycombinator.com