DC-DC battery charger under hood?

[martnH]

I think dc-dc charger is a good idea when:

-cranking battery and auxillary battery are of different type
-remote distant charging
-vehicle has smart alternator.

Otherwise it may not be a good idea as

-Dc-dc may charge the battery slowly
-You will not be able to combine batteries for winching or jump start (well you can use a jump cable

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[msand1977]

I have an ArkPak with an AGM battery in back of my 2014 4runner. While driving it only charges at 6 amps, and I was thinking with a DC-DC charger I could get more like 20-40 amps. I like the simplicity of a DC-DC charger and I'm pretty sure my 4runner has smart Alternator. I like this one by Iron Man 4X4 http://www.ironman4x4.com/products/dual-battery-systems/40a-dc-to-dc-battery-charger , but its not available in the US yet.

 

[john61ct]

I have an ArkPak with an AGM battery in back of my 2014 4runner. While driving it only charges at 6 amps, and I was thinking with a DC-DC charger I could get more like 20-40 amps. I like the simplicity of a DC-DC charger and I'm pretty sure my 4runner has smart Alternator. I like this one by Iron Man 4X4 http://www.ironman4x4.com/products/dual-battery-systems/40a-dc-to-dc-battery-charger , but its not available in the US yet.

CTEK Dual may be enough, otherwise go Sterling.

If that box has a BMS or charger, make sure you bypass, go direct to batt terminals.

And charger goes right there, shorter run the better.

 

[kevman]

-- A B2B still requires the same size wiring. Amps is amps. A B2B will help with voltage drop, but you still need properly sized wires.

I thought it was common practice to use a larger gauge wire to reduce voltage drop when charging straight from the alternator. The Redarc states a 4AWG wire is required for the 1240D to run 30ft. If your alternator is at 14.7 volts, 40 amps over 30ft. reduces this to 14.1V at the battery. In order to have a charging voltage of 14.4 you would need to size up to a 1/0 AWG wire. So I thought the DC-DC charger would let you get away with a smaller, more manageable, wire.

The alternator outputs 165amps

It does, but not many peoples battery banks can take that kind of charge. If you have a 200Ah battery bank a 40A charger is right at the charging sweet spot assuming .2C.

I understand you are under the impression that dc-dc charge will charge battery faster
And this is all marketing ****************...

Not faster, but fast enough. I thought that after the battery is done the bulk stage the current to finish charging is reduced. Most of the time spent charging a battery is in the slower absorption stage which a 40A charger on a 200Ah bank would be more than adequate.

As for marketing, what about battery life? Is there truth to a 3-stage charger being better for your batteries? If so, considering the price of an ACR and MPPT is about the same as a DC-DC charger wouldn't the DC-DC charger be a better choice for your batteries longevity?

 

[john61ct]

Your wires must still be sized to safely carry the max amps.

Yes less concern about voltage drop, but tgat's with the DCDC at the target bank.

Cheapest is the Alt wired heavy to the House bank, then a little Echo Charger back to Starter.

But test the Alt puts out proper v&a, and temps don't get too high.

DCDC certainly easier for noobs, but good ones at high amps are pricey.

 

[martnH]

-- A B2B still requires the same size wiring. Amps is amps. A B2B will help with voltage drop, but you still need properly sized wires.

I thought it was common practice to use a larger gauge wire to reduce voltage drop when charging straight from the alternator. The Redarc states a 4AWG wire is required for the 1240D to run 30ft. If your alternator is at 14.7 volts, 40 amps over 30ft. reduces this to 14.1V at the battery. In order to have a charging voltage of 14.4 you would need to size up to a 1/0 AWG wire. So I thought the DC-DC charger would let you get away with a smaller, more manageable, wire.

The alternator outputs 165amps

It does, but not many peoples battery banks can take that kind of charge. If you have a 200Ah battery bank a 40A charger is right at the charging sweet spot assuming .2C.

I understand you are under the impression that dc-dc charge will charge battery faster
And this is all marketing ****************...

Not faster, but fast enough. I thought that after the battery is done the bulk stage the current to finish charging is reduced. Most of the time spent charging a battery is in the slower absorption stage which a 40A charger on a 200Ah bank would be more than adequate.

As for marketing, what about battery life? Is there truth to a 3-stage charger being better for your batteries? If so, considering the price of an ACR and MPPT is about the same as a DC-DC charger wouldn't the DC-DC charger be a better choice for your batteries longevity?

If I run 3*100ah batteries, they will pull 100amps. Now the little baby dc-dc will not +be able to do that.

If I run 1*100ah battery, then it may pull 40amps. Again the little baby dc-dc maybe able to do it. Yes like you said for bulk charging.

I don't get it why would you need your second battery to maintain the cranking battery. Just use a battery charger......It will not prolong the battery lifespan. Just don't discharge the lead acid completely

So yeah.dc-dc is a waste of money (in most cases But I will give you that their marketing is pretty good

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[john61ct]

If I run 3*100ah batteries, they will pull 100amps.

How do you know?

Even if true, would only be for a very short time.

A properly sized DCDC is very effective.

I agree that they are expensive, and many people think they are required when they could do without.

 

[john61ct]

Investing in DC electrics infrastructure has two goals.

A. Don't flatten the Starter batt from House loads.

B. Get House bank recharged, ideally back to 100% Full as quickly and as often as possible.

The alt is rarely a significant contributor to the latter, except for 5-7 hour driving days.

Solar is usually the best place to start spending money.

Solar alone is ideal if you can do that, if not then a small quiet genny can help give an hour or two Bulk start early in the morning, solar completing the long tail at lower amps.

Regular access to mains of course reduces the need for other sources, then it's just the bank capacity vs the consuming loads.

 

[DiploStrat]

I thought it was common practice to use a larger gauge wire to reduce voltage drop when charging straight from the alternator. The Redarc states a 4AWG wire is required for the 1240D to run 30ft. If your alternator is at 14.7 volts, 40 amps over 30ft. reduces this to 14.1V at the battery. In order to have a charging voltage of 14.4 you would need to size up to a 1/0 AWG wire. So I thought the DC-DC charger would let you get away with a smaller, more manageable, wire. ...

The primary purpose of a B2B is to change the voltage from whatever your alternator puts out to whatever your battery needs. Typically, you want a B2B on a vehicle with a low charging voltage (e.g. Toyota at 13.9v) when charging an AGM or FLA that wants 14.2v+. In order to do this, the wiring has to be large enough for the B2B to lose some amps boosting the voltage. Thus REDARC, for example, fuses their 40A B2B at 60A. CTEK and Sterling are also very clear about their wiring requirements. (This ignores, for the moment, LiFePO4 which may actually want a voltage drop.) Since most of the largest B2B's put out less than 50A, their wiring requirements will be smaller than might be optimal for a direct connection through a relay. But even here there is a dirty secret - even with the largest cables, the charge rate on most rigs will quickly drop to around 50A as the camper battery builds up a surface charge.

...
As for marketing, what about battery life? Is there truth to a 3-stage charger being better for your batteries? If so, considering the price of an ACR and MPPT is about the same as a DC-DC charger wouldn't the DC-DC charger be a better choice for your batteries longevity?

A three stage charger is "best" but almost all chargers out there, including your car's alternator, are multi-stage of some sort. Basically, most chargers start out with high voltage and high amperage. The amperage that a lead acid battery will take is largely determined by its internal voltage - as that rises, the amp flow drops off naturally. This produces the transition from bulk to absorb charge. Once the battery forces the amp flow down to a pre-determined level, the charger will drop the voltage to its float level. So it is partly a natural result of rising voltage and partly the design of the charger.

As an aside, this is why most B2B's drop the voltage of the starter battery down to 13v - to trick the vehicle's alternator into remaining at full output until the camper battery is fully charged.

So no, a B2B isn't automatically going to make your battery last longer. The secret to long lead acid battery life is achieving a full charge and, as most batteries require hours of absorb charge, this is very hard to do without solar or shore power to complete the process. Your vehicle is great for the first, bulk stage of charging, but you will probably need solar or shore power to finish the job.

So, except for differing on the value of the alternator, I agree with john61ct, above. (That's why I have 600w of solar and two solar controllers.)

 

[kevman]

I agree that they are expensive

To me though, when redesigning a system from scratch, they don't seem that expensive. Considering they replace both the MPPT controller and the ACR they're not far off.

 

[john61ct]

I agree that they are expensive

To me though, when redesigning a system from scratch, they don't seem that expensive. Considering they replace both the MPPT controller and the ACR they're not far off.

I have no idea why anyone would think a DC-DC charger would replace a solar controller.

Unless you're buying some combined unit and think that'll be enough for you?

Totally different functionality, multi-purpose gadgets are rarely best of breed.

And they are one-way only, so if you have a different charge source on the DCDC B side you want to keep A bank charged, you'll still need an combiner.

Or God forbid, a second DCDC

 

[big_willy_wanderer]

Lot of misinformation in this thread.
Alot of AGM batteries (high performance) and some deep cycle and even hybrids like higher chargeing voltages than modern alternators can put out. So, using the ctek d250sa and smart pass120. Her are some if the benefits:
1. Isolation of the two batteries (starter and service)
2. Over current protection
3. Low voltage protection
4. If the starte battery doesnt have enough juice to start the vehicle....the smartpass will use the service battery to administer 10 second doses of highpower to allow the vehicle to start
5. You can connect non-critical electrical consumers like fridge and led lights to the smartpass- while the alternator is running they will charge off that rather than siphoning draw from the service battery that you are trying to charge. If the voltage onthe service battery gets below 11.5 volts , those non-critical consumers are auto disconnected until the service battery is charged up past 11.5 volts again. Meanwhile, critical items like beer coolers and HAM radios are run directly off the battery....lol

 

[martnH]

Lot of misinformation in this thread.
Alot of AGM batteries (high performance) and some deep cycle and even hybrids like higher chargeing voltages than modern alternators can put out. So, using the ctek d250sa and smart pass120. Her are some if the benefits:
1. Isolation of the two batteries (starter and service)
2. Over current protection
3. Low voltage protection
4. If the starte battery doesnt have enough juice to start the vehicle....the smartpass will use the service battery to administer 10 second doses of highpower to allow the vehicle to start
5. You can connect non-critical electrical consumers like fridge and led lights to the smartpass- while the alternator is running they will charge off that rather than siphoning draw from the service battery that you are trying to charge. If the voltage onthe service battery gets below 11.5 volts , those non-critical consumers are auto disconnected until the service battery is charged up past 11.5 volts again. Meanwhile, critical items like beer coolers and HAM radios are run directly off the battery....lol

Any old tech voltage sensing relay can do that....You do not need a dc-dc charge to do that.


Dc-dc's biggest marketing point is that it can charge battery faster and many ppl buy dc-dc for its "performance". And this is simply false advertisement. Especially when ppl buy 25amps baby dc-dc.

Why pay more for mediocre gain?

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[john61ct]

Again, all depends on the context many variables involved.

It isn't rocket science to use an ammeter to test what charging volts you're getting at the target location, and compare to the bank's specs.

If too low, see if going to heavier gauge wire will help. Over very high amps and long distances, sometimes buying a DCDC is actually not much more than the rewiring job.

If one bank is LFP and all the other infrastructure is designed for lead, higher voltage than you want, then a DCDC is a good solution.

Just because many (most) are purchased unnecessarily, does not mean they aren't ever useful.

 

[DaveInDenver]

Dc-dc's biggest marketing point is that it can charge battery faster and many ppl buy dc-dc for its "performance". And this is simply false advertisement. Especially when ppl buy 25amps baby dc-dc.

Why pay more for mediocre gain?

That's also a generalization. It might be faster to have a constant 25 A rather than a potential 100 A that doesn't have sufficient forcing voltage to achieve a significant proportion of it. The advantage of a DC-to-DC charger is decoupling one side from the other so that constant power is transferred rather than a current that is a function of voltage.

It's true they may often be used unnecessarily but there are also plenty of cases where they do add value, mainly predictability. You can more reliably say it will take 'x' amount of time to recover 'y' amount of energy into a battery regardless of what percentage of their theoretical max at which your sources are performing.