Possible consequences of dropping battery voltage - Page 1
Forum section: electronics / beginners

author: Damn The Man
author_rank: Newbie
timestamp: August 07, 2023, 09:51:05 am
content: Hello all, first post here!I have a question that I cannot seem to get a straight answer to so this seems like the right place to ask.I have been running a guitar amplifier (model Spark 40) on a drill battery for a while now. This is a fairly standard thing that people seem to do. The amp requires 19v DC and will work happily on an 18-20v battery as far as I can tell. My question is to do with the voltage dropping off as the battery discharges. If the battery had built in undercharge protection I assume it would not be a problem, but I have been using an old Milwaukee battery and just out of interest I hooked it up to a multimeter and a big 33ohm resistor the other day to see when it would shut off. I guessed about 16v.I was a little surprised when it got down to 15.4v and called the experiment off.Could this drop in voltage cause damage to the amplifier? Sorry if this is a bit of a broad question, please let me know if this is not enough information.Thanks in advance!.

author: Psi
author_rank: Super Contributor
timestamp: August 07, 2023, 09:57:42 am
content: Lithium battery have low voltage cutouts, but if it's a NiMH or NiCa I doubt it will have a low voltage cutout.It's pretty uncommon for a lower than normal voltage to cause damage to things.I don't know how a Spark 40 works inside, so I cant really say. But it's unlikely to damage anything.

author: RoGeorge
author_rank: Super Contributor
timestamp: August 07, 2023, 10:07:30 am
content: It depends of the power tool model + its battery type.If the battery pack is Li-Ion, it must have over discharge protection. Li-Ion are irreversibly damaged by low voltage, they usually come with a battery management board that disconnect the load automatically. The BMS is usually inside the battery pack, but could be possible to be inside the power tool instead (though highly unlikely), I'm not familiar with the model you are using.If the battery pack is a much older technology, for example a NiCd battery pack, that usually doesn't have any under voltage protection, though it won't get damage either.

author: Damn The Man
author_rank: Newbie
timestamp: August 07, 2023, 10:34:30 am
content: Thank you both for the information. It is a lithium battery pack, I will have to look up the model number later to see what the deal is with the under-voltage protection.Just to continue the train of thought, if the voltage was to continue to drop (for example if using a variable power supply) would this be likely to damage electrical devices in general? I'm only talking about DC, for example a laptop?Sorry if this is basic stuff but I have googled this many times and only ever get conflicting information and usually about AC power.

author: Shonky
author_rank: Frequent Contributor
timestamp: August 07, 2023, 10:41:53 am
content: An "18v" pack is 5 cells in series. So 15V is still 3V per cell assuming the BMS is doing its job. Li Ion can go down as far as 2.7 or even 2.5 but most BMSes will drop out by about 3V if not earlier. So you're probably pretty close.

author: Psi
author_rank: Super Contributor
timestamp: August 07, 2023, 12:15:41 pm
content: yep, the low voltage cut-off on lithium batteries is usually a last-resort/failsafe sort of thing. It doesn't kick in until things are really bad. Not something you want to reach often, or at all.

author: u666sa
author_rank: Frequent Contributor
timestamp: August 07, 2023, 02:21:39 pm
content: You can use 160 watt lenovo notebook power supply to power it.

author: BeBuLamar
author_rank: Super Contributor
timestamp: August 07, 2023, 10:11:18 pm
content: Running the battery voltage to real low would hurt the battery rather than the amplifier. At low voltage the amplifier would distort and deliver low volume but it's not going to be damaged.

author: Damn The Man
author_rank: Newbie
timestamp: August 08, 2023, 08:01:01 pm
content: Thank you to everyone for the answers. I knew this was the right place for the information!

author: Manul
author_rank: Super Contributor
timestamp: August 08, 2023, 08:37:44 pm
content: Quote from: Damn The Man on August 07, 2023, 09:51:05 amSome think that lower than nominal voltage can never hurt. It is not completely true. FYI there is one scenario which is not unheard of. It is the issue of undervolting stepdown switching converters. For example, in a buck converter input current is roughly proportional to input/output voltage ratio. So given a constant load at the output, when input voltage is lower, input current is higher. If the design is marginal, higher current might blow the switching mosfet. Same applies to some other topologies, like isolated converters. But all this is rare and is a sign of a bad design.

author: Damn The Man
author_rank: Newbie
timestamp: August 09, 2023, 11:42:55 am
content: I was considering a buck/boost converter to keep the voltage constant. Good to know the possible limitations .

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: August 09, 2023, 02:35:37 pm
content: There are battery boosters around, such as this one used by radio hams to give a rock solid 13.8 Volts from a lead acid battery.https://mfjenterprises.com/products/mfj-4416cThe construction of similar inverters and protection circuits is not particularly difficult, although a little over the top to drive a battery powered guitar amp.SJ