Buck-Boost converter 12V battery to 13.8V 5A?

[augustinetez]

After the mention of these 5A DC-DC XL4005 adjustable step-down module in another thread, has anybody seen a 5A rated Buck/Boost converter outputting 13.8V?

Input would be a 12v battery (and possibly attached charger), so input volts would be in the range of ~10v - 16V.

Usage is for low power portable transceiver if they weren't overly noisy/easily suppressed.

 

[Nigel Goodwin]

To do that you would obviously need a step-up/step-down module, as you need to do both.

Exactly what are you trying to do?, the mention of 13.8V looks like you've seen the nominal voltage of a lead acid 12V battery and are wanting to maintain that for some reason?. A low power transceiver should be designed to work from the battery 'as is', no need to do anything - just connect it to the car battery.

 

[rjenkinsgb]

Something like this is about as near as you will get in an all-in-one unit.

That can take vehicle 12V in and give stabilised 12V, 15V or various other voltages out.

100W 12-24V UNIVERSAL NOTEBOOK LAPTOP CAR CHARGER AC POWER SUPPLY ADAPTER BLACK | eBay

Power: 100W. 1 x Laptop Power Adapter. Adapter Size: 20cm x 10cm/7.87" x 3.94" (Approx.). Due to the light and screen setting difference, the item's color may be slightly different from the pictures.

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[augustinetez]

Exactly what are you trying to do?, the mention of 13.8V looks like you've seen the nominal voltage of a lead acid 12V battery and are wanting to maintain that for some reason?. A low power transceiver should be designed to work from the battery 'as is', no need to do anything - just connect it to the car battery.

Some older stuff, while yes, designed to used "in a car", was not designed to used on top of a mountain where there are no cars - possible use #1 - I'm assuming you've heard of SOTA operation?

Other stuff is designed to be battery powered, but falls miserably short with just a small drop in battery voltage - possible use #2.

#3 - why do I need a reason, other than just out of curiosity?

There are several circuits for DIY jobs in QST/QEX/CQ magazines etc and I was curious as to whether there were any cheap modules around already built.

 

[Nigel Goodwin]

Some older stuff, while yes, designed to used "in a car", was not designed to used on top of a mountain where there are no cars - possible use #1 - I'm assuming you've heard of SOTA operation?

Other stuff is designed to be battery powered, but falls miserably short with just a small drop in battery voltage - possible use #2.

#3 - why do I need a reason, other than just out of curiosity?

There are several circuits for DIY jobs in QST/QEX/CQ magazines etc and I was curious as to whether there were any cheap modules around already built.

If your power requirement actually that high?, or would lower be OK - if so cheap modules are available:

3pcs DC-DC Boost Buck Adjustable Step Up Step Down Automatic Converter XL6009 Module Suitable For Solar Panel

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You're considerably limited by your requirement for step up and step down.

One easy option would be to step UP (to say 18V) then step DOWN from there to 13.8V - but that's essentially what the step up/down converters are doing anyway.

Here's a 5A step up:

LM2587 DC DC Boost Converter 5A 3-30V Step Up to 4-35V Power Supply Module

Only US$7.99, buy best lm2587 dc dc boost converter 5a 3-30v step up to 4-35v power supply module sale online store at wholesale price.

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And a 5A step down:

Geekcreit® 5A XL4005 DC-DC Adjustable Step Down Module Power Supply Converter

Only US$1.39, buy best geekcreit® 5a xl4005 dc-dc adjustable step down module power supply converter sale online store at wholesale price.

www.banggood.com

 

[augustinetez]

Most low power rigs would get away with 2-3A, I prefer to be a little cautious and leave a little headroom 'just in case'.

A trawl through Ebay and the likes throws up plenty of 3A ones like your first one and I did come across a 5A one but it needed an input voltage of min 15V to supply the current and voltage, so kinda defeats the purpose.

 

[Nigel Goodwin]

Most low power rigs would get away with 2-3A, I prefer to be a little cautious and leave a little headroom 'just in case'.

A trawl through Ebay and the likes throws up plenty of 3A ones like your first one and I did come across a 5A one but it needed an input voltage of min 15V to supply the current and voltage, so kinda defeats the purpose.

As I've repeatedly told you, your requirement needs BOTH a step-up and a step-down, either a single module, or (as it more likely for 5A) a pair of modules. You can't step down from a car battery to maintain 13.8V.

 

[sagor1]

A portable transceiver will probably get lots of hash noise from any buck/boost converter, they are all switching power supplies. From what I've seen, most portable transceivers (ie 5W to 10W) will operate ok down to about 11V, so a regular battery will do as-is. Put on a small solar charger if you want to maintain the voltage a bit longer...