Power for amp at outdoor gig

[1958Bassman]

I don’t think you are understanding how this works.

If a bass amp is rated to draw 3 amps at 1/8 power (fairly large amp), the sizing for battery life is based on this long term average by multiplying the current by the line voltage giving 360 watts, then multiplying by the inverter efficiency of say 80% or 420 watts.

Now you look at the battery capacity. Multiply the AH by the voltage and you get watt-hours. Say your battery is 12V and 100 AH, that would be 1200 Watt-hours but a standard lead acid car battery has discharge limits of about 50% which gives you 600 watt-hours of capacity.

Now, divide the capacity by the load and you end up with the hours of run time, or in this case 600WH/420W or about an hour and a half.

For inverter SIZING, it must be capable of supporting the dynamic load which includes the short term peak currents. A good rule of thumb for class D bass amps is roughly 50% of the audio power, converted back to AC line current. So if the amp was rated at 800 watts into the load being driven, that would be 400 watts, which is the minimum the inverter would need to be rated for independent of the battery side of things.

I have worked with audio, AV, musical instrument/PA amplification and 12V audio for over 45 years- I also repair boats, including the electrical systems- I'm pretty aware of real world applications for this.

I have a 400W inverter- it's not very big and it wouldn't like to power a bass amp for long. I use it for charging batteries for my power tools and sometimes, for my laptop. Its rating might be called 'optimistic', but I haven't tested it- I don't expect it to do hard work for that price.

We actually agree on some of this- the load side needs to be known before the battery side.

Battery reserve capacity is rated in Amp-Hours- it's right there on the label. You can't use a battery until it's dead and reserve capacity reflects the battery type's ability to maintain its voltage under load.

The link is for a company that works with marine electrical systems and the company owner is an Electrical Engineer-

Battery Bank Capacity Calculation | Pacific Yacht Systems

 

[Plain Old Barry]

After seeing all the replies, I think you should post what is your spending limit, how long is the gig/s, how many times will you be doing this. I can see some of the options are getting expensive, but more info is needed to give you the best option.

Excellent point.

Generator Rentals - Tool Rental - The Home Depot

Lots of locally owned options, too. This is also a good idea when not sure of what you want or really need.

I'm not normally a fan of big box stores, but my two local Home Depot locations have far newer power equipment in far better condition than the locals. They seem to turn it over a lot more often. For example, every spring for the last 15+ years, I rent a large rototiller to prep my wife's garden. The rear tine Honda I rent seems to be brand new every three years or so.

 

[agedhorse]

I have worked with audio, AV, musical instrument/PA amplification and 12V audio for over 45 years- I also repair boats, including the electrical systems- I'm pretty aware of real world applications for this.

I have a 400W inverter- it's not very big and it wouldn't like to power a bass amp for long. I use it for charging batteries for my power tools and sometimes, for my laptop. Its rating might be called 'optimistic', but I haven't tested it- I don't expect it to do hard work for that price.

We actually agree on some of this- the load side needs to be known before the battery side.

Battery reserve capacity is rated in Amp-Hours- it's right there on the label. You can't use a battery until it's dead and reserve capacity reflects the battery type's ability to maintain its voltage under load.

The link is for a company that works with marine electrical systems and the company owner is an Electrical Engineer-

Battery Bank Capacity Calculation | Pacific Yacht Systems

Marine batteries, deep cycle batteries, car batteries and he’ll cells/AGM’s are all rated differently. The AH rating is very much dependent on both the design of the cells and the discharge rate. The discussion started out with car batteries which are very different in construction and rating. That’s what the derating of capacity is for, though it may be a bit high for low amperage loads.

 

[lug]

So, what's the best battery technology for Metal?

 

[Al Kraft]

So, what's the best battery technology for Metal?

I'm going to guess nickel metal hydride, for what I hope is an obvious reason.

 

[1958Bassman]

Marine batteries, deep cycle batteries, car batteries and he’ll cells/AGM’s are all rated differently. The AH rating is very much dependent on both the design of the cells and the discharge rate. The discussion started out with car batteries which are very different in construction and rating. That’s what the derating of capacity is for, though it may be a bit high for low amperage loads.

The reserve capacity is totally dependent on those factors but the reason I mentioned marine batteries is due to their having higher reserve than most car batteries and the ability to discharge more deeply than a cranking battery. The OP asked about using batteries- car batteries aren't the best choice for this application.

 

[agedhorse]

The reserve capacity is totally dependent on those factors but the reason I mentioned marine batteries is due to their having higher reserve than most car batteries and the ability to discharge more deeply than a cranking battery. The OP asked about using batteries- car batteries aren't the best choice for this application.

Agreed.

My choice would be one of the Lithium ion chemistries, similar to what’s being used in the new battery powered lawnmowers. The (useable) power density and practicality is beyond impressive IMO.

 

[seamonkey]

So, what's the best battery technology for Metal?

I'm going to say Flywheel Batteries
The Big Heavy Metal Flywheels

 

[1958Bassman]

Agreed.

My choice would be one of the Lithium ion chemistries, similar to what’s being used in the new battery powered lawnmowers. The (useable) power density and practicality is beyond impressive IMO.

Pacific Yacht Systems guy talks about Carbon Foam batteries- haven't seen one yet, but they sound interesting.

 

[Passinwind]

Agreed.

My choice would be one of the Lithium ion chemistries, similar to what’s being used in the new battery powered lawnmowers. The (useable) power density and practicality is beyond impressive IMO.

By any chance did you pay any attention to the slew of one-off electric race cars VW were doing a couple of years ago? They chose two extremely challenging venues to run record attempts at, Pikes Peak and the Nordschleife circuit at the Nürburgring. Really cool stuff.

 

[Plain Old Barry]

By any chance did you pay any attention to the slew of one-off electric race cars VW were doing a couple of years ago? They chose two extremely challenging venues to run record attempts at, Pikes Peak and the Nordschleife circuit at the Nürburgring. Really cool stuff.

A few years ago, someone ran two electric exhibition cars in a Formula 2000 race I attended at Lime Rock Park. The electrics were spec'd to the same weight as the 2 liter IC cars and had to meet the same rules. On LRP's short 1.5 mile road course, the electrics actually did really well, especially in the higher torque areas like an uphill and through short chutes between corners. This was maybe 4-5 years ago, and I'm sure today's tech would probably destroy the exhibition cars.

It was just a bit weird that they sounded like R/C cars as they ran the circuit.

Personally, I've been in the R/C airplane hobby since the early 90's, and I've only flown LiPo powered electrics for at least five years. Plenty of power, super dependable, quiet and clean.

If anyone gets a chance to drive a Tesla, I'll only say... try it!

 

[Passinwind]

A few years ago, someone ran two electric exhibition cars in a Formula 2000 race I attended at Lime Rock Park. The electrics were spec'd to the same weight as the 2 liter IC cars and had to meet the same rules. On LRP's short 1.5 mile road course, the electrics actually did really well, especially in the higher torque areas like an uphill and through short chutes between corners. This was maybe 4-5 years ago, and I'm sure today's tech would probably destroy the exhibition cars.

It was just a bit weird that they sounded like R/C cars as they ran the circuit.

Cool, I attended several races at Lime Rock back in the classic Trans-Am and Can-Am era. The VW didn’t just break the Pikes Peak electric record, they took the all time overall mark to boot. Electric cars don’t care about a 14,000 finish and big torque is a huge bonus for a hillclimb. And yep, Formula E cars sound like sewing machines to me, pretty much. Weird, but maybe not quite as weird as the old Howmet turbine cars I saw run at Watkins Glen, which you could hear nearly wherever they were on the track.

 

[seamonkey]

If anyone gets a chance to drive a Tesla, I'll only say... try it!

They are cool, but hold off buying one until the "Right to Repair" acts are in place.
The Teslas have very little moving parts and will last forever, but the batteries won't.
A few cells in the huge battery arrays are going to fail after the warranty ends. A few broken cells will render the whole battery pack as broken. You'll want a competent local independent shop to be able to reach in an replace the bad individual cells. Tesla would want to replace the whole 1000lbs battery pack and charge you shipping.

You'll save $15,000 if a qualified tech can replace just the individual bad cells.

 

[agedhorse]

Since the battery pack is a safety certified assembly (anjd for VERY good reasons), I believe you will find that it's not economical to replace individual cells once the pack is out of warranty (8 years and ~150k miles for the model 3) anyway. The cells are closely balanced and monitored (the control system for EV battery packs is complicated) as well as active management (electronic and thermal) on a cell by cell (there are thousands of individual cells) or grouping of cells (module) basis. Same for the inverter drive units and the motors, just too involved for some shade tree mechanic to "wing". Tesla has a program in place to remanufacture battery packs rather than outright replacement as much of the cost if the battery pack is in the containment structure, cooling and management system. Once this is in place (most Tesla failures outside of mechanical damage) are still covered under warranty), it's expected that a remanufactured pack will run under $10k installed. Teslas are starting to show up with 200k miles with good battery packs, so IMO they have done their homework.

Battery chemistry is constantly being fine tuned, costs are declining. I think it will be less dramatic than it seems.

 

[Al Kraft]

Since the battery pack is a safety certified assembly (anjd for VERY good reasons), I believe you will find that it's not economical to replace individual cells once the pack is out of warranty (8 years and ~150k miles for the model 3) anyway. The cells are closely balanced and monitored (the control system for EV battery packs is complicated) as well as active management (electronic and thermal) on a cell by cell (there are thousands of individual cells) or grouping of cells (module) basis. Same for the inverter drive units and the motors, just too involved for some shade tree mechanic to "wing". Tesla has a program in place to remanufacture battery packs rather than outright replacement as much of the cost if the battery pack is in the containment structure, cooling and management system. Once this is in place (most Tesla failures outside of mechanical damage) are still covered under warranty), it's expected that a remanufactured pack will run under $10k installed. Teslas are starting to show up with 200k miles with good battery packs, so IMO they have done their homework.

Battery chemistry is constantly being fine tuned, costs are declining. I think it will be less dramatic than it seems.

Interestingly enough Toyota and Toyota Prius owners (including fleets) were quite surprised at the longer than anticipated/projected life the battery packs their early cars got. I recall reading an article where several folks who tracked this across fleets of vehicles (like company cars) had very convincing log book evidence.

 

[Old Fart]

 

[okcrum]

I've played the PHX Rock 'n Roll Marathon and Heart Walk for the last 7 years (other than 2020) and the organizers of both events quickly realized they needed a 5-7 kVA Honda generator on every street corner where they had a band setting up (dozens) along the routes. No muss, no fuss, no science fair power projects, no noise.

 

[seamonkey]

It's kind of interesting to see towing company logos on pickup trucks hauling around gas generators. They give a quick charge to get you 40 miles to the next charging station.

 

[Plain Old Barry]

Interestingly enough Toyota and Toyota Prius owners (including fleets) were quite surprised at the longer than anticipated/projected life the battery packs their early cars got. I recall reading an article where several folks who tracked this across fleets of vehicles (like company cars) had very convincing log book evidence.

I don't claim this as statistically significant, but my BIL's beater car is a 2002 first generation Prius with 150,000+ miles, still on the original drive battery. The engine start battery has been replaced twice, at a higher cost than a typical car battery but not horrendously expensive.

The large corp I work for has a decent number of G2 and 3 Prius' nationwide, mainly in large metro areas like NYC and Chicagoland, and I've not heard of really any battery issues. Some have incredibly high miles on them, others spend lots of time sitting and have extremely low miles. The only real complaint is service times are extended due to in-house mechanics not trained on hybrids having to take them to dealers.

 

[1958Bassman]

A few broken cells will render the whole battery pack as broken. You'll want a competent local independent shop to be able to reach in an replace the bad individual cells. Tesla would want to replace the whole 1000lbs battery pack and charge you shipping.

You'll save $15,000 if a qualified tech can replace just the individual bad cells.

Battery banks need the cells to be similar and new cells mixed with old isn't a good way to go if some are out of acceptable range. They need to come up with a decent exchange program in order for out of warranty battery replacement to be viable.