I'm going to be doing a lot of outdoor events and busking this summer and I am looking for better battery options for my mini amps. I've been using a Fender Mustang Mini for several months now, I am pleased with the sound, but the battery life is very low. 3 hours max with 8 C batteries. I recently bought a Vox Mini 5 because the battery life is longer and you can set it to low -wattage modes, I got it with the hopes that I could find a sound that I enjoy with that amp but I still like the sound of the Mustang Mini better. So I looked around a bit and found that some folks have modified their AC powered amps to run off of Gel Cell batteries. Does anyone know how to go about doing this? I'm a complete noob at any of this, btw
How to modify mini amp to run off Gel Cell batteries?
- Thread starter jcarlos
- Start date
I have done something similar with a video camera setup, and also separately with a mobile DJ setup, so maybe my experience can help you.
My first impression is that these amps with 8 batteries are all looking at a 12 volt power source. You can confirm this if you have the AC adapter and look at the OUTPUT voltage specification of the adapter. Either that, or look at the label plate on the back of the amp where the AC adapter plugs in.
If this is true for 12 volts, there are a few simple things you can put together that will give you what you want. Heck, you can even use a car battery - but we'll get to that later...
Basically you need to match the plug end that is on the AC wall adapter, not the part that goes into the wall, but the part that goes into the AMP. These are called 'barrel plugs', and if you look at it and the mating receptacle in the amplifier you will see that there is an INNER contact and an OUTER contact, one is positive and one is negative and this is important to know which is which, because this is the POLARITY of the plug, typically referred to as 'center-positive' or 'center-negative' and there is no absolute standard, and if you get it wrong, and your amp does not have a blocking diode in the power circuit, you can actually fry the power circuit of your amp, so this is the first thing to figure out.
The next step is to decide if you want to fabricate a custom solution, mostly buying all the parts online, and are comfortable with using a soldering iron, or you want to strap together a few pre-made items that will give pretty much the same end result, all of which should be available off-the-shelf locally.
For the sake of brevity and simplicity I will go with the latter, pre-made solution, and if you need the custom one instead, let me know.
Once you have identified the polarity and size of the DC barrel plug on the AC adapter, you need to source another cable or plug of the same specifications. However, exactly what that cable is depends upon the next part.
For a gel-cel or seal-lead-acid (SLA) battery that lasts a long time (with lower amperage draw), comes with it's own charger and even has a cigarette lighter socket or two for powering accessories, you might want to consider a 'portable jump start unit'. The items have the features I mentioned but also have a pair of jumper cables attached and can typically help to start a car with a low battery. This all works to your advantage since most of the time these are 12 volts and at least 7, 10 or 15 amps continuous output possible with about 150 amps in burst output (of which you'd get maybe 3 shots before the battery's energy is spent and needs to be recharged - typically overnight).
These unit can be had at most stores for like $50 for a basic model and can typically be recharged/discharged about 1,000 time before the internal battery is too sulfated to be used any more. Replacement batteries can be had online for about $20, and you have to open the unit with a screwdriver, and void the warranty to replace the battery, but it's up to you.
A few examples can bee seen on Amazon here, and if you scroll down a bit there is a Schumacher Xp400 for $39 which is maybe a starting point:
I had one of these, with a cigarette lighter 4-way splitter running a video rig, powering a video camera, portable LCD monitor, 50 watt halogen spot light, and wireless mic receiver for 6 hrs continuously before the battery was spent. I dont remember exactly but I think that total power consumption was around 80 watts. I was very impressed. I actually had a fully charged second unit as a backup, but never needed it that day.
I also used a car battery fixed to a video trolley, with a cigarette lighter 4-way splitter to power a much larger setup when taping a parade years ago, and that rig was in use for 9 hrs straight and never ran out of power. For DJ equipment I had build a wooden box to hold 4 deep-cycle Marine batteries, and each one had a 400-watt DC-to-AC converter to run an entire huge DJ rig for a block party for 4 hrs, with power left over.
If you go with the portable jump start, the only thing you really need to do is find a cable that has the matching DC barrel plug that is wired at the other end to a cigarette lighter socket plug. Radio Shack used to have many pre-made ike this, and also had one where the DC barrel plug was changeable, what they called the 'tip' and you would get one 'tip' free with the cable, and could buy others if/when needed - the only thing is to pay attention to the polarity when installing the 'tip' to the cable..
So once you get the right 'power cable' from Radio Shack (maybe like $8-$10), you plug one end into your portable amp, and then the other end into the portable jump start in the 12v 'accessory socket' and you are good to go.
What I did on mine was to tape up the big alligator clips first with electrical tape and then duct tape over that, and some folks either just cut them off (and tape up really well the bare ends of thick wire), or open the unit and disconnect them from the inside, and you want to make sure that these alligator clips do not have the positive and negative touching each other because you can get a really nasty 400 amp spark that will stop your heart and knock you flat on your back (ever touch a fresh 9volt battery to your tongue? it's like that but a million times stronger), and also the battery can explode if they make contact with no electrical resistance such as a car battery attached to the ends.
The only other thing to be aware of is the AMPerage draw of your amplifier. This is important for to reasons:
1) fuse: If you amp is pulling say 5 amps or 5,000 mA from the DC adapter, you need to make sure that you have at least a fuse of that spec for the power cable. if you have a 2 amp fuse, once the amp pulls more than 2 amps from the battery, the fuse will blow and you have no power. Mind you, this amperage is NOT the AUDIO circuit which might be 5 watts or 10 watts, which is totally different, this is DC current going from the battery into the amp's DC power plug in the back. You can see what amperage it has in 2 places, one is on the AC wall adapter, where is shows DC OUTPUT VOLTAGE it should also say something in amps, which is either like 5A, or 5,000 mA, which is the same, the latter being milliamps - the other location is on the back of the amplifier where the wall adapter plugs in, and the same markings might be on the label plate near the power plug jack.
2) runtime: how many amps, watts, volts etc determines the approximate run time of your power source based upon load.
This comes from Ohm's Law. The simple application is that you have 12 volts, and you know both the DC wattage and amperage draw of the amplifier (listed on the AC adapter and on amp) so you can calculate the approximate runtime as in HOW LONG will the battery run and still be effective buy calculating for AMPS or amp-hours.
I'll spare you the lengthy explanation and theory, this page can go deeper if you want more details, for now lets go with this:
I went to this calculator
and for Voltage, I put in 12 (volts)
for Power, I put in 60 (watts)(get this off the back of the amp, or the power adapter)
and hit calculate, and it gives me back 5 amps.
This means that all other things being equal, while also dependent upon things like ambient temp, and battery 'health' you might get as much as 5 hours of use for the battery at this continuous load of 60 watts draw from the amp, and there are variables that we cannot account for in the electronics involved that relate to 'efficiency', which is basically just electrical resistance such that a small amount of energy from the battery is not converted 100% for use by the amplifier and is basically wasted as heat.
For the most part, this is not really something you can control in a consumer-level device and because of that we should figure that 5 hours is the 'maximum potential' runtime, whereas real world use will probably be somewhere about 10-15% less.
So you have a cable and a battery pack. These jump start units come with their own wall adapter for charging, which typically takes overnight.
[due to message size limitation I've continued this in my next post]
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[continuing from first post]
If you need MORE runtime that a single one of these provides, you can buy two of them, and go the second one when the first one runs out. Or to lower the power draw and load on the first one, maybe use the second one that has a different cable that includes internally what is a called a BUCK converter, which is a circuit that has a 7805 voltage regular or similar that will step-down the DC voltage from 12 volts from the battery to 9 volts for your guitar pedals if you use them. Radio Shack also used to sell such a cable that goes from the cigarette lighter plug to the adapter tips that has a switch to select the output voltage from 3v, 4.5v, 6v, 9v, etc, but you need to get one that is also capable of at least 2 AMPS, as the cheaper ones are typically only around 200mA which is enough to charge a cel phone, or maybe power 1-2 guitar pedals, but if you have a multi-effect pedal it may have higher current requirements.
All of the above can be easily modified or adapted to your needs, if as given, this is not exactly what you want.
Please let me know if you need me to clarify anything, or have any questions, as this kind of stuff is fun for me, and if my experience can benefit you in any way, I am only too happy to be of service.
-Booli
If you need MORE runtime that a single one of these provides, you can buy two of them, and go the second one when the first one runs out. Or to lower the power draw and load on the first one, maybe use the second one that has a different cable that includes internally what is a called a BUCK converter, which is a circuit that has a 7805 voltage regular or similar that will step-down the DC voltage from 12 volts from the battery to 9 volts for your guitar pedals if you use them. Radio Shack also used to sell such a cable that goes from the cigarette lighter plug to the adapter tips that has a switch to select the output voltage from 3v, 4.5v, 6v, 9v, etc, but you need to get one that is also capable of at least 2 AMPS, as the cheaper ones are typically only around 200mA which is enough to charge a cel phone, or maybe power 1-2 guitar pedals, but if you have a multi-effect pedal it may have higher current requirements.
All of the above can be easily modified or adapted to your needs, if as given, this is not exactly what you want.
Please let me know if you need me to clarify anything, or have any questions, as this kind of stuff is fun for me, and if my experience can benefit you in any way, I am only too happy to be of service.
-Booli
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I think you are talking about an INVERTER. The problem with using an inverter is that you are taking DC from a battery, then plugging in an INVERTER to convert to AC, and then converting AC back to DC via using the AC/DC adapter to power the amplifier.
Doing so is pretty inefficient and lots of power will be lost as most consumer-level inverters are only aout 60% efficient. And the typical AC/DC wall adapter (wallwart type) are only about 40% efficient, so you are actually throwing away a lot of the energy from the battery that will get wasted as heat and never be utilized by the amplifier.
If the amplifier has a DC input, it cost less money and around 85% of the energy from the battery can be utilized by the amplifier without waste or conversion.
Your suggestion here for the inverter is useful and would be applicable if the amplifier can ONLY be powered by AC mains and not inbuilt battery pack or via an AC/DC wallwart adapter which typically has a transformer inside.
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Thanks for the info Booli, everything was super helpful. I think the best solution for me would be the jump start kit, I found this one
http://www.walmart.com/ip/Cobra-Electronics-Jump-Starter-Powerpack-500W-120V-AC-Output/14649556?action=product_interest&action_type=title&placement_id=irs_middle&strategy=PWVUB&visitor_id=66294993900&category=0%3A91083%3A1045959%3A1074767%3A1043587&client_guid=c87aa2c2-b63f-41cd-898e-63231e0c0952&config_id=0&parent_item_id=13035281&guid=4e886766-9792-421f-a8bd-d33bc7dd988f&bucket_id=irsbucketdefault&findingMethod=p13n
and it has a 100watt AC inverter built in.
The Mustang Mini and the Vox are both 5 watts. How long do you think one of those will run either amp? And usually how long do they take to recharge?
http://www.walmart.com/ip/Cobra-Electronics-Jump-Starter-Powerpack-500W-120V-AC-Output/14649556?action=product_interest&action_type=title&placement_id=irs_middle&strategy=PWVUB&visitor_id=66294993900&category=0%3A91083%3A1045959%3A1074767%3A1043587&client_guid=c87aa2c2-b63f-41cd-898e-63231e0c0952&config_id=0&parent_item_id=13035281&guid=4e886766-9792-421f-a8bd-d33bc7dd988f&bucket_id=irsbucketdefault&findingMethod=p13n
and it has a 100watt AC inverter built in.
The Mustang Mini and the Vox are both 5 watts. How long do you think one of those will run either amp? And usually how long do they take to recharge?
That Cobra unit has lots of feature that seem overkill for being a big battery source, and I dont see that it has a lighter socket plug.
If you used the amplifier's wall adapter and go into the inverter on this one, you may find that your runtime is about 25%-30% shorter than if you go from 12v DC lighter socket to the dc barrel plug on the back of your amplifier. Also the jumpstart unit is going to get really hot, too hot to touch, near the area where you plug in to the inverter due to energy being wasted as heat
It's because of 'efficiency' or lack thereof. Look up 'electrical efficiency' to find out more. It's the main reason your electric bill is much lower when you use fluorescent or LED lighting as opposed to incandescent lighting. Incandescent bulbs waste LOTS of energy as heat and are only typically 15% efficient.
To get AC power from a DC source such as a battery, you are using a circuit that has both a rectifier and a transformer, because of the inherent resistance of each, you will lose some POWER (in watts) and CURRENT (in amperes)
now if you use the amplifier's wall adapter INTO the inverter, you are in fact converting power, now a SECOND time, from the AC plug of the inverter to the amplifier's wall adapter, out the barrel plug to the jack on the back of the amplifier, so again you are using a circuit that has both a rectifier and a transformer, because of the inherent resistance of each, you will lose some POWER (in watts) and CURRENT (in amperes)
because of the POOR efficiency of each conversion, and the fact that you are needlessly converting electricity twice this way (DC to AC, then AC back to DC), you are LOSING what is typically about 30% of the POWER of the battery, dissipated as heat, measured in WATTS, which will shorten runtime, and reduce the load it can handle at one time. The increased heat inside the jumpstart enclosure will also significantly shorten the effective useful service life of the battery inside.
You said the amplifiers are 5 watts - is that AUDIO power to the speaker, or the power it pulls from the wall - these are different things entirely.
Audio power that drives the speaker at a certain volume level measured in decibels, when they say 'its a 10 watt amplifier' that is in fact COMPLETELY different than the electrical power to run the electronics, which is a factor of amperage and voltage, from Ohm's Law:
amps x volts - watts, so 5 amps x 12 volts = 60 watts, this is NOT the speaker watts, but the electrical watts required from the power source.
Before I keep going in this direction, please let me know if this makes any sense to you...
Also, on Fender's web site, they say the Mustng Mini takes 6 x C batteries, so this is 9 volts (6 x 1.5=9), and you need a cable like I said in the other post above that has a selector switch for the output voltage so you can easily go from the 12v of the jumpstart down to the 9v that the Mustang Mini needs. Some energy will be dissipated as heat (typically via a single nickel-sized heatsink that is fixed to the back of a 7805 integrated circuit inside the fat end of the cable), but not a lot, and typically will only impact the battery runtime about about 5-8%.
Ok, battery life is really the main goal of me spending more money on a thing like this, and 8% loss is waaay better than the 35% if I use the inverter. Can you send me links to the parts that I would need to get things going. Im a bit confused about the fuse part. Where does the fuse go exactly? Do I need to make modifications to any of the parts(the jump starter, or the cigarette lighter) to get it working? I might eventually use a couple of pedals that I would also like to power.
Here are the pics of the Mustang Mini, I dont know what the actual power draw is.
http://jestergallery.com/pics/20140307_195646.jpg
http://jestergallery.com/pics/20140307_195828.jpg
Also how long did it take to recharge your jump starter once the battery was drained?
Here are the pics of the Mustang Mini, I dont know what the actual power draw is.
http://jestergallery.com/pics/20140307_195646.jpg
http://jestergallery.com/pics/20140307_195828.jpg
Also how long did it take to recharge your jump starter once the battery was drained?
sorry for the delay in responding...
ok, those pictures help a lot.
Can you post pictures of the VOX amp as well, for the same areas of the VOX?
Sometime today or tomorrow, I'll try to put together a shopping list for you, with direct links to the items...
-Booli
ok, those pictures help a lot.
Can you post pictures of the VOX amp as well, for the same areas of the VOX?
Sometime today or tomorrow, I'll try to put together a shopping list for you, with direct links to the items...
-Booli
Here are the Vox pics
http://jestergallery.com/pics/VoxPic 2.jpg
http://jestergallery.com/pics/VoxPic 1.jpg
http://jestergallery.com/pics/VoxPic 2.jpg
http://jestergallery.com/pics/VoxPic 1.jpg
