Say folks; I've noodled on this dilemma for a bit, and keep getting thwarted (either by cost or feasibility) - so will outline my thoughts versus "what am I missing"?!

I need a 12v-14v DC supply at 150 Amps, from Lead-Acid (not LiPo - the obvious choice - due to cost consideration) batteries: With Pb cell sag, most deep-cycles drop below 12v quickly - even in parallel - and the inverter that it's powering is intolerant of over 15v nor under 11. So, I was going to go "up" in B+ (in series, nominally to 16v-18v; e.g. 3x 6v cells), then regulate back down to just over 12v., since "15v batteries" aren't really a thing. Even seeking a 2vdc, high current capacity cell to put in series with a standard 12v lump is oddly cost-prohibitive. Similarly switching boost converters would be great - but again, 'not seeing high current versions out there.

If it was an order of magnitude less current, I'd use a 3-terminal linear regulator and a pass transistor; voila! I don't much care about power loss/dissipation, but don't seem to find affordable collector-current bi-polar or FETs that fit the bill... Perhaps I could parallel an array of NPNs in pass, but (although potentially inexpensive) I'd wonder about matching and somewhat distributing the current paths across several xistors <?>.

Alternatively, since I have power to squander, I considered an easier approach by use of diode drops: There are 150A rectifiers at under $10@, so I could string some of these, forward biased, to expend the excess voltage ".7v-at-a-time". This is certainly inelegant, and not exactly cheap, as I would need five or so of them :-( ...There you have it! I'd love to hear about an angle that I have not explored yet; so T.I.A.!!

 

The diodes also have a negative temperature coefficient.
They cannot be used reliably as ballasts for bipolar transistors.

 

At those power levels, approximately 1.8 kW, your choices are limited. I suggest you look into various SMPS (Switch Mode Power Supply) alternatives that might be compatible with your objectives. I don't think there will be ANY cost-effective solutions, all of them will probably require components on the expensive side. It is not dissimilar from the desire of many hams to have 1.5 kW linear amplifier. Those are hardly cheap, and your objective won't be either.

 

It seems to me the inverter voltage range is ok. A 12V Lead acid battery should not go to 15V or be run to under 11V anyway. If the voltage is dropping to 11V when the battery is charged, the battery is probably too small a capacity for the job and/or the leads are not heavy enough.
It may be better to get a new inverter that runs at a higher input voltage like 24V or even 48V for those power levels.

 

How about using a series of dropping resistors (heavy gauge wire for 150 amps) and a batch of contactors to act as shunt relays (starter solenoids?) actuated by comparator-ladder network to switch out the segments one by one (maybe 1/2 volt each) to maintain a reasonably level voltage input to the inverter? Crude, but potentially very effective.

 

Say folks; I've noodled on this dilemma for a bit, and keep getting thwarted (either by cost or feasibility) - so will outline my thoughts versus "what am I missing"?!

I need a 12v-14v DC supply at 150 Amps, from Lead-Acid (not LiPo - the obvious choice - due to cost consideration) batteries: With Pb cell sag, most deep-cycles drop below 12v quickly - even in parallel - and the inverter that it's powering is intolerant of over 15v nor under 11. So, I was going to go "up" in B+ (in series, nominally to 16v-18v; e.g. 3x 6v cells), then regulate back down to just over 12v., since "15v batteries" aren't really a thing. Even seeking a 2vdc, high current capacity cell to put in series with a standard 12v lump is oddly cost-prohibitive. Similarly switching boost converters would be great - but again, 'not seeing high current versions out there.

If it was an order of magnitude less current, I'd use a 3-terminal linear regulator and a pass transistor; voila! I don't much care about power loss/dissipation, but don't seem to find affordable collector-current bi-polar or FETs that fit the bill... Perhaps I could parallel an array of NPNs in pass, but (although potentially inexpensive) I'd wonder about matching and somewhat distributing the current paths across several xistors <?>.

Alternatively, since I have power to squander, I considered an easier approach by use of diode drops: There are 150A rectifiers at under $10@, so I could string some of these, forward biased, to expend the excess voltage ".7v-at-a-time". This is certainly inelegant, and not exactly cheap, as I would need five or so of them :-( ...There you have it! I'd love to hear about an angle that I have not explored yet; so T.I.A.!!

Consider high-current voltage regulator ICs like LM138 or LM338, or consult a professional engineer for a custom solution. Explore online electronics communities for specific advice. Prioritize safety in your design.

 

While a 48V solution is truly much more practical to have... here's a 12V approach. Consider that the whole semiconductor industry is built on "lots of same", so follow that approach. To build a 10A buck regulator is pretty easy these days, and they can be had to permit external synchronization of the switching frequency. I'll assume for a current-mode regulation scheme that there is a way to enforce reasonable current sharing among a group of identical buck stages. Maybe even use only one (or two) voltage sensing stages to simplify that amount of the design. Add a master oscillator and a 1-of-16 decoder so that you can generate a 16 phase signal set to clock 16 of these identical little 10 Amp buck stages.

Or make a single board with 4 each 10 A buck stages, although this will take some beefy copper to handle 40A and the appropriate caps needed to make it work right. If the board has an added 1-to-4 decoder on the synchronizing signal then a simple master oscillator with (1-to-4 decoder) 4-phase output keeps four such boards humming nicely, with 160A capacity. Good luck testing this!

 

What is the application?

 

Say folks; I've noodled on this dilemma for a bit, and keep getting thwarted (either by cost or feasibility) - so will outline my thoughts versus "what am I missing"?!

I need a 12v-14v DC supply at 150 Amps, from Lead-Acid (not LiPo - the obvious choice - due to cost consideration) batteries: With Pb cell sag, most deep-cycles drop below 12v quickly - even in parallel - and the inverter that it's powering is intolerant of over 15v nor under 11. So, I was going to go "up" in B+ (in series, nominally to 16v-18v; e.g. 3x 6v cells), then regulate back down to just over 12v., since "15v batteries" aren't really a thing. Even seeking a 2vdc, high current capacity cell to put in series with a standard 12v lump is oddly cost-prohibitive. Similarly switching boost converters would be great - but again, 'not seeing high current versions out there.

If it was an order of magnitude less current, I'd use a 3-terminal linear regulator and a pass transistor; voila! I don't much care about power loss/dissipation, but don't seem to find affordable collector-current bi-polar or FETs that fit the bill... Perhaps I could parallel an array of NPNs in pass, but (although potentially inexpensive) I'd wonder about matching and somewhat distributing the current paths across several xistors <?>.

Alternatively, since I have power to squander, I considered an easier approach by use of diode drops: There are 150A rectifiers at under $10@, so I could string some of these, forward biased, to expend the excess voltage ".7v-at-a-time". This is certainly inelegant, and not exactly cheap, as I would need five or so of them :-( ...There you have it! I'd love to hear about an angle that I have not explored yet; so T.I.A.!!

How long do you need to be able to draw 150A from your batteries? Realize that even with deep discharge lead acid cells, you can't use more than 50% of the batteries capacity or you will kill the battery.

In my opinion, you are dismissing LiPO4 batteries too quickly since they eliminate your problem entirely. Lithium batteries have a very flat discharge curve and the output voltage varies from 12V (10% of capacity) to 12.8V (Fully charged). Lithium cells are also capable of output an astounding amount of current. For example, Headway 38120 cells are typically rated at 8AH, but are capable of sourcing 200A for short periods of time (~2 minutes). The price of prismatic cells has also come down a lot in the last year. For example 3.2V, 280AH LiFePO4 cells are now selling for $65 each on Alibaba. I built a 25.2V, 280AH battery for my RV out them, and they were $100 each 2 years ago.

 

I have seen circuits that use an inverter/diodes scheme in series with a load to hold the voltage up, so that the load device wll operate correctly. But at 150 amps that will be a challenge, the design I saw was good for ten amps max.
With a lot more information about the application and the inverter this group may come up with a solution, it has happened before. The big challenge is that not enough information supplied leads to a lot of guesses.

 

Consider high-current voltage regulator ICs like LM138 or LM338, or consult a professional engineer for a custom solution. Explore online electronics communities for specific advice. Prioritize safety in your design.

I'm curious about the note above; as those are low current devices (5A), we'd still be looking at at pass transistor/array. I am a retired E.E., so the safety factor is a given; it's the cost/performance situation with which I'm dealing. Thx for the reply, nonetheless!

 

I have seen circuits that use an inverter/diodes scheme in series with a load to hold the voltage up, so that the load device wll operate correctly. But at 150 amps that will be a challenge, the design I saw was good for ten amps max.
With a lot more information about the application and the inverter this group may come up with a solution, it has happened before. The big challenge is that not enough information supplied leads to a lot of guesses.

I can provide a bit more; my standard 2000W <nominal; 2500W-peak> 12vdc-120vac automotive inverter is being fed by "some" form of battery: At the 1440W draw level, even a parallel pair of new 12vdc healthy lead-acid car batteries (or even deep cycle marine) batteries very quickly drop below their initial charge level, causing the low-voltage protection circuit of the inverter to cut-out, then restart: It's not an inrush-surge issue, but rather a very fast depletion of the nominal 12v needed by the inverter.

To combat that (and not have to buy a new/expensive 2000W 24vdc-in inverter), I "just" need to boost the vdc-in to the 12-15v level desired by the inverter: So - per 'commodity' parts - either I series the batteries to 24, and 'chop' off ~10v <trying to avoid PWM/Smoothing, but could>...without wasting all of that in heat. Non-commodity cells (of 3v, 100Ah) do exist, but are obscenely expensive as compared with readily available battery configurations. Oddly a trio of 6v batt's in series presents less-to-lose (e.g. drop 4v), so that form of forklift traction battery might be a reasonable surplus alternative. ...'Hope the above helps.

 

Your Batteries are grossly under-rated for the job at hand,
possibly the connecting Cables as well.

The solution will NOT be inexpensive.
.
.
.

 

Here is a radical suggestion that should work: Replace all, or maybe just most, of the existing inverter with a circuit that can work with a lower supply voltage. a duty-cycle regulated PWM inverter. What is the output voltage of the present inverter, and how well does it need to be regulated?? There may be a different design that can work very well with a widely changing supply voltage.

OR is the inverter the high voltage supply for a tube-type linear amplifier for dominating some CB radio channel. (This is just an unfounded wild guess, so please do not be offended by it). Just let us know what the inverter is powering, there may be a better approach.

 

Rather effective IC for 100-200 A step-down tiny voltage muliphasic (thatswhy so large amperage) converter are used in all computer core feeding. Just inspect the standard circuitry. The typical solution is Intersil HIP6301--> HIP6602--> bunch of FETs. https://html.alldatasheet.com/html-pdf/67183/INTERSIL/HIP6301CB/1635/5/HIP6301CB.html

 

Your Batteries are grossly under-rated for the job at hand,
possibly the connecting Cables as well.

The solution will NOT be inexpensive.
.
.
.

As I have tested with two feet of 1/0 (and checked IR drop across), I'm less concerned with the short run of copper. I'd agree that - at this point - the battery pile is the source of the issue. I am now, in fact, considering looking for an inexpensive 6v battery to series, having only (dis/re)charged it to around 3v. Thanks for inputs - and if affordable LiPo's come my way...*problem-solved*!

 

As I have tested with two feet of 1/0 (and checked IR drop across), I'm less concerned with the short run of copper. I'd agree that - at this point - the battery pile is the source of the issue. I am now, in fact, considering looking for an inexpensive 6v battery to series, having only (dis/re)charged it to around 3v. Thanks for inputs - and if affordable LiPo's come my way...*problem-solved*!

That's not a good solution, sorry. A 6V battery that supplies only 3V is critically undercharged and will be hazardous to use normally in that state.

 

As I mentioned in post #4, the 12V battery should never be discharged to 11V and a 6V defiantly to 3V. That is the way to kill the battery very quickly.
You really are trying to do this the wrong way.
Either you need a number of new 12V batteries in parallel to increase the capacity, (not just one or two batteries but many for that load for more than a few miniuts. For batteries, more is better I think! ) or a similar number in series to boost the voltage and go to a higher voltage inverter. To try to draw 150Amps from a car battery for any length is a great way to kill it.
It is like you are trying to run a car on a lawnmower motor.

 

Here is a radical suggestion that should work: Replace all, or maybe just most, of the existing inverter with a circuit that can work with a lower supply voltage. a duty-cycle regulated PWM inverter. What is the output voltage of the present inverter, and how well does it need to be regulated?? There may be a different design that can work very well with a widely changing supply voltage.

OR is the inverter the high voltage supply for a tube-type linear amplifier for dominating some CB radio channel. (This is just an unfounded wild guess, so please do not be offended by it). Just let us know what the inverter is powering, there may be a better approach.

Fair inputs - and appreciated: The inverter is tasked with feeding a 120vac EVSE (Electic Vehicle Level-1 Charger). Its max consumption (during intial "pre-stepdown" charging power decrements) is stated to be ~1.4KW, reducing with charge level of the EV. ...One of the compromises that I'm trying to avoid is swapping EVSE's for a lowered-trickle version; e.g. rather than initially run at 12A-15A, it can be throttled to 8A. The good news is that it should drop the load on the inverter/batteries such that it won't cut out - with the bad news of protracted recharging duration! - - 'Continued appreciation for the inputs, folks!

 

That's not a good solution, sorry. A 6V battery that supplies only 3V is critically undercharged and will be hazardous to use normally in that state.

So I surmised; so why I was (half-heartedly) considering a trio of 6v cells running at a "less depleted" ~5v or so: Just under 15v doesn't ostensibly upset the inverter's over-voltage cut off <fingers-crossed>.