Amateur radio voltage booster circuitry

[cowana]

I have an IC-7000 radio, which I use when mobile (running from a gell cell battery).

However, a limitation of the radio is that it is designed to be run from an inverter at 13.8v. Once the voltage of a gell cell starts to fall, the output power of the radio falls very quickly. The radio gives out 100w at 13.8v, but only 70w at 12v.

This is an issue, as gel cells spend most of their discharge cycle between around 12.5 and 11.5v. The radio uses a maximum of 25A at 13.8v.

There I two solutions I can see:
1) Use two batteries in series, giving 24v. Then use a switching regulator such as **broken link removed** to reduce the voltage 13.8v.
2) Use one battery, then a boost regulator **broken link removed** to up the voltage to 13.8v.

Any thoughts or suggestions? Obviously two batteries in series would result in a longer run time as the current being taken out the batteries would be greatly reduced. The second product I linked to above seems like a very simple circuit - any ideas what the part number of the ICs used might be?

Thanks for any thoughts,

Andrew

 

[tronitech]

Why not use 7 x 2V 25Ah cyclons?

 

[ronsimpson]

I would use a boost regulator. It would boost the 12V to 13.8V. So any voltage below 13.8 will get boosted up. Any voltage above 13.8 will pass through. One battery is simple. Using two batteries brings up more problems, like balancing the batteries so they discharge and charge at the same rate.

Batteries should not be discharged all the way down. I would set the PWM to shut down at 11 volts. (Or maybe 10 volts) It is possible to boost 6 volts to 13.8 but the battery will not like that.

The ebay boost converter is what I would do. It is only good for about 10A???

 

[cowana]

I would use a boost regulator. It would boost the 12V to 13.8V. So any voltage below 13.8 will get boosted up. Any voltage above 13.8 will pass through. One battery is simple. Using two batteries brings up more problems, like balancing the batteries so they discharge and charge at the same rate.

Agreed- that's the issue to avooid that was concerning me.

Batteries should not be discharged all the way down. I would set the PWM to shut down at 11 volts. (Or maybe 10 volts) It is possible to boost 6 volts to 13.8 but the battery will not like that.

The simplest protection is just a low voltage buzzer - that way I can swap to a new battery when needed.

The ebay boost converter is what I would do. It is only good for about 10A???

Well noticed! I saw the 'up to 25A current' part and was convinced - while in reality it'll only do about 10A constantly. I'm quite happy to make my own boost regulator instead of making one - many switching regulator datasheets even have sample PCB layouts.

 

[ronsimpson]

Try this.

 

[rumpfy]

Something is not quite right.
Lead acid cells have a maximum voltage per cell of around 2.15 Volt. Times 6 gives 12.9 volt as a maximum.
For battery charging, a voltage around 14.4 volt is used.
Presumably the radio is SSB, and if so the current drain is a function of the PEP of the radio. Thus the average current drawn from the supply is quite variable.
You say the unit is used 'mobile' and presumably this means in a motor vehicle. If so, then with the motor running, the vehicle system voltage would be over 14 volt and this would relate reasonably well with the 13.8 volt source. Given the power of the radio and from what you say, it seems that you have a separate battery to power your radio. If so, you must obviously charge it somehow.
One matter I notice is the often overlooked effect of the power lead resistance and the quality of the connections. It is truly amazing to see the conductor gauge of the wire used to supply these car audio amps; you know, the 500 watts units.
Can I suggest you do a detailed examination of your set up with the primary goal of eliminating voltage drop in the supply cables and I would consider to run the radio from the vehicle electrical system.
Hope I'm not trying to teach you to suck eggs, but the approach to use boosters etc seems to me to be the wrong approach because the radio is designed (presumably) to operate off 12 battery systems.
If this was your preferred option(to use a regulator), my preference would be to use 24 volt and chop it down to 13.8. With the boost approach, the peak current in the switching transistor is twice the average DC current and could be up to 50 amp going by your figures. Designing switching regulators at this current level is not easy and requires close attention to heatsink design. Your observation about a proprietary booster unit and its inability to run at 100% of the time is EXACTLY what I'm saying. It aint easy; I've done a switching regulator to run a 12 volt water pump from a 24 volt system in a Toyota bus, and the heatsink and the winding design was critical. For a transformer core, I used a yoke ring from a 110 degree colour TV. The conductor gauge you would need would be around 3 to 4 mm diameter and the overall conversion efficiency is rather low due to the saturation voltage of the switching device.
The cyclons are nice batteries and I have used them in a calibrator, but they are a bit too small for your needs. Seven big ones will cost at least $200 to $250 (probably more). I dont think that is the way to go.
Hope this helps.

 

[ronsimpson]

Something is not quite right.

With the boost approach, the peak current in the switching transistor is twice the average DC current and could be up to 50 amp going by your figures.

(boost) No! If the battery is at 6.5 volts and the output is at 13 volts then the "twice" comment is true. If the battery is at 12 volts the input current is 1.08x. The switch current is 1.08x.

(buck) It is true the current from a 24 volt battery is 1/2 that from a 12 volt battery. While the average current from a 24 volt battery is 0.5x the peak current through the switch is 1X.

 

[cowana]

Try this.

That looks like a great circuit - I'll give it a try!

Something is not quite right.
You say the unit is used 'mobile' and presumably this means in a motor vehicle. If so, then with the motor running, the vehicle system voltage would be over 14 volt and this would relate reasonably well with the 13.8 volt source. Given the power of the radio and from what you say, it seems that you have a separate battery to power your radio. If so, you must obviously charge it somehow.

That's the issue. If I use the radio from a running motor vehicle, there is no issue as the alternator keeps the battery at ~13.8v. However, I tend to use the radio from separate (smaller) batteries, such as 11Ah gel cells. I charge these from a trickle charger, which isn't able to supply the current required for the radio. When not charging, as you say, the maximum is around 12.9v (although this falls quite quickly).

One matter I notice is the often overlooked effect of the power lead resistance and the quality of the connections. It is truly amazing to see the conductor gauge of the wire used to supply these car audio amps; you know, the 500 watts units.

I agree about the audio amp comment - people often seem to use very thin wires for connecting big amps and speakers up! My radio has 12AWG wires and gold plated bullet connectors - you get less than 100mV drop over the two meter power lead (measured under load).

Andrew

 

[unclejed613]

you don't need the trickle charger, or the gel cells if you're running this in a vehicle.

 

[rumpfy]

The circuit provided by ron is OK as far as it goes.
The critical design and construction points are with the inductor, switching transistor and the forward diode and the heatsinking. I'm not familiar with the selected IC. You should refer to OnSemi application note AN920-D and read the advice starting on page 19.
The operating frequency of rons design is around 70 to 100 KHz and this is probably too high. At these frequencies, the winding wire for the inductor should be litz wire, and due to the low input/output voltage, the diode should be high current (>30 Amp) Schottky type and similarly with the switching transistor.
I calculate the peak current to be around 27 Amp where the operating frequency is around 50KHz.
You should carefully note the advice in AN920-D concerning construction techniques. construction would be easier at lower frequencies (< 50 KHz).
Heat sinking of the semiconductors is necessary and the 30 Volt /60 Amp rating for the switch seems OK but you need to be sure that the saturation Voltage of this device is 'lower' rather than 'higher'. Much of the device dissipation is due to 'on state' voltage of the transistor(FET). Same remarks go for the diode because its forward voltage drop is important too.
Some of the commercial power supplies I see these days in TV sets etc., are quite smartly engineered from both the electrical and the thermal/mechanical point of view. they often use power factor correction but this aspect isnt relevant to you.
Good luck to you if you make rons design, but please read AN920 first.

 

[KeepItSimpleStupid]

This is a reminder to use a deep cycle battery.

 

[rumpfy]

As a postscript, and out of interest, I downloaded a copy of the manual and the brochure for the radio.
The brochure says that the radio uses 22 Amp at max transmit power. In my previous posting, I quoted 27 Amp peak current in the booster circuit. I based this 27 Amp figure on a 10 Amp average input current. if the correct value is actually 22 Amp, then the peak current in the booster is 60 Amp. Based on this information, I go back to my original posting where I said to consider the battery and the power installation. With 60 Amp peak current flowing around the place, the booster would be an engineering nightmare. The use of the radio away from a high current power source (like a vehicle battery) is going to be a problem for you. The gel cells you use, are no doubt under rated for the job they are being asked to do. 22 Amp from a 10 Amp Hr battery is just flogging the batteries.

 

[unclejed613]

the difference between 100W and 70W is only about 1db. but i still think you would be better off eliminaying the trickle charger and gel cells, unless you intend that this radio is also a pack portable. in that case ditch the trickle charger...