12V ups system for audio

[brxxthe]

Hello

I am building a 12v system to power a cart full of audio gear that also has ups backup to lead acid. I am using a samlex 1235 power supply to create 14v which feeds all of the 12v audio gear and a samlex bbm 1225 which steps down the 14v to trickle charge the lead acid (33ah) and seamlessly connect the system to the battery if the power supply loses A/C input. Make sense?

Firstly, I want to be able to use two batteries and be able to 'hot swap' them. For example let's say 1 battery is connected and is being trickle charged. Then I connect a low battery. I don't want the dead battery to suck all the juice from the charged one, or from the rest of the system (if running off the batts,) yet I still want it to begin charging from the 13.5 volts from the power supply. Make sense?

Secondly, the audio gear can handle up to 16v. Problem is, I'm getting quite a voltage drop when feeding from the battery and not the 14v power supply. What can I do to make the transition from 14v to batt backup, so that my voltage suddenly doesn't drop from 14 to 11? I want to be able to run 15 to 20 amps of 12vdc from this 30amp power supply and a single OR pair of 33ah batteries (1 batt for shorter run time and less weight) and I want the voltage at the gear to stay around 13-14 Volts from 10 to 20 amps.

 

[tcmtech]

Without getting complicated you are basically stuck with the voltage drop issue. Lead Acid batteries charge at around 13.8 - 14.5 volts and once the charging system is removed they will allways drop to below there 12.6 volt unloaded voltage if they have any power draw on them.

Also as the load increases the internal resistance of the battery will creat more internal voltage drop and at some point a smaller highly loaded battery can drop below 11 volts and less despite being fully charged.

Why do you need a hot swappable power source for an audio system?

 

[brxxthe]

This power system is for my mobile sound recording rig for film work. I only have space on my cart for two 33ah batteries. If I am to be running on battery power all day, I want to be able to have 4 more batteries which are fully charged on a camera or equipment truck 5 minutes away. This way as I lose charge on my batts, they can be swapped out with full ones every few hours - if I'm not going to have access to AC.

 

[mneary]

You just need a BBM-1225 for each battery. Connect the input terminals of both of them in parallel to the 1235 power supply. Connect the output terminals of both BBM-1225s in parallel and to your load. Connect each battery to the battery terminals of its own BBM-1225.

The diodes inside the BBM-1225 give your load the best voltage from the 3 possible sources: If the 1235 is on, it will be 14V because that's more than either battery. If there's no 14V, then the diodes in the 1225's will choose the best battery. When you hot-swap. the new battery will take over seamlessly (assuming it is better). If the new battery is low, the circuit may try to charge it, but it will be limited to a factory preset of about 4A through the resistors.)

When the AC power is restored, the 1235 will be 14V and will supply the loads. The resistors in the BBM-1225's will trickle charge the batteries if they can.

You might want to run this by the service people at Samlex.