DC / DC Converter or Equalizer ?

[Beausoleil]

I've got a dock neighbor who has a 24V house system in his sportfisherman, with a smallish 24/12Vdc converter for his radios and other 12V electronics. He just purchased a couple of big 12V electric trolling reels, and has temporarily tapped directly off his batteries to use them, but now wants to do it right.

He showed me the quote he got from a marine electrician and asked my opinion. I thought it was a little high and could be done for less money, but I don't think he was being gouged. The electrician proposed to use a Vanner 24/12 equalizer (military-grade). I was wondering which is preferred in the marine environment - an equalizer or a dc/dc converter?

Not being a power guy, I'd assume that all things being equal, a dc/dc converter would be preferred because the output would be held at 12V (or 13.8V), whereas the equalizer's 12V output would be actually just half of whatever the battery bank voltage would be - under the assumption that the electronics in an equalizer were simpler than the switch-mode design of an actual DC/DC converter. And since this is for trolling reels in an exposed environment, I'm guessing the ground should be isolated in either case...

Any recommendations for him?

[David M]

Most electronics you put on a boat should be rated for a marine environment....mostly for corrosion reasons, safety reasons or ignition source reasons.

Given it is a 24 volt system, there are probably at least two pairs of 12 volt batteries in his boat that are wired in series. Unless he has four 6 volt batteries which are wired in series, which would also solve the problem. If it is a big powerboat chances are likely that it has more than two 12 volt batteries in series.

You can get 12 VDC across the POS and NEG terminal of any single 12 volt battery even with it being charged by a 24 volt charger as a 24 volt battery bank. Get a multimeter and check it out.

The reason for this is a batteries internal resistance.

The potential problem here is that the battery you are drawing off of will be at a lower voltage and therefore lower charge state than the battery it is connected to in series. If it is an intermittent draw, like a powered fishing reel would be, then I would not worry about it. If it is a constant draw then you would probably want to install an equalizer which is a device that converts a higher DC down to a lower DC...so that the battery being drawn from can be kept topped up.

Only with an application that has a much higher draw would you want to consider installing a 12 VDC charger to keep the one 12V battery with the greater load topped up. The downside to this idea is it would require the genset to be running to power the charger.

[Beausoleil]

As I (indirectly) said, that's how it's set up now. I should have been more specific: the DC systems are 24V - engines, alternators, charger, etc. He tapped 12V from one half of the 24V bank, and now wants a permanently wired system which would meet ABYC recommendations. So which would be the preferred route: an equalizer or a dc/dc converter?

I guess the question is: which is better in the long run - replacing chronically overworked 12V batteries in a 24V bank, or doing the proper thing and installing a true 24/12V system. The boat's a recent vintage Hatteras sport-fisherman, so I'd think he's decided to do it right rather than keeping jury-rigged.

Edit: my statement about me not being a power guy meant that I don't do power electronics and such for a living, although as an EE I have more than just a passing knowledge of it. Telecom and computer networks are my specialty. I'm sure there are members of this board who do this stuff for a living... IOW - don't keep the responses simple, I'm a big boy and can handle it!

[speciald@ocens.]

I have a 24v. supply for my house, winches, inverter, etc. And a separate 12v. supply for my electronics and engine starting. Requires 2 separate battery chargers and alternators. Expensive, but probably the best way to do it.

[David M]

Does the boat have a genset that is normally on while cruising?

If this is the case then I would buy a single 12 volt battery that is dedicated to the purpose of powering the fishing reel and whatever other 12 volt loads need to be powered on board. This is better than compromising his 24 volt system by drawing power from one of the two batteries in series causing a reliance on an equalizer working.

My philosophy about this is to isolate as many systems from each other as is practical so that if one system fails, it does not bring down another system.

[Beausoleil]

Originally Posted by David M

Does the boat have a genset that is normally on while cruising?

If this is the case then I would buy a single 12 volt battery that is dedicated to the purpose of powering the fishing reel and whatever other 12 volt loads need to be powered on board. This is better than compromising his 24 volt system by drawing power from one of the two batteries in series causing a reliance on an equalizer working.

My philosophy about this is to isolate as many systems from each other as is practical so that if one system fails, it does not bring down another system.

The reels would be used while trolling under power - the boat is a sportfisherman, not a sailboat. So the 24V bank would be continuously charging.

I was leaning towards recommending he go with the equalizer setup, since the loads are non-critical motors (he might disagree when if he ever charters!). My thinking was that a DC/DC converter was more for truly voltage-critical loads like sensitive electronics like an SSB, not electric motors.

And I'd want to make sure that anything I recommend won't come back to bite him later, like the possibility of a non-isolated system causing problems like electrolysis or a floating ground/negative on the 12V side.

[Sailboats Rock]

Hello again!
With my Morgan, I only have an 8hp Johnson with no alternator. However, I want to be able to operate a microwave and heater at the same time or maybe heater and tv at the same time. What are the best ways to recharge the batteries while out on the water? All of my lighting has been converted to portable LED lighting. So, there is no drain on the batteries there. I am thinking most you may tell me solar panels. With that said, I guess I would need to know more about the sizes to get and possibly the best place to mount them for the best response.

[Beausoleil]

Originally Posted by Sailboats Rock

Hello again!
With my Morgan, I only have an 8hp Johnson with no alternator. However, I want to be able to operate a microwave and heater at the same time or maybe heater and tv at the same time. What are the best ways to recharge the batteries while out on the water? All of my lighting has been converted to portable LED lighting. So, there is no drain on the batteries there. I am thinking most you may tell me solar panels. With that said, I guess I would need to know more about the sizes to get and possibly the best place to mount them for the best response.

That would best be answered under its own thread - very different from the preferred method of deriving 12V from 24V...

[foggysail]

Originally Posted by speciald@ocens.

I have a 24v. supply for my house, winches, inverter, etc. And a separate 12v. supply for my electronics and engine starting. Requires 2 separate battery chargers and alternators. Expensive, but probably the best way to do it.

Just a comment--- an alternator's output is controlled by the field excitation. A 12v alternator should work fine outputting 24vdc with the right regulator. Unfortunately, most alternators today use internal regulators that force their usage to particular voltages.

I have both 12 and 24vdc systems for similar usage as you use yours. The 24v bank relies on an inverter/charger (one of the old Freedoms). The 12V bank accepts charge from both alternators and a 50 ampere 3 stage charger.

Foggy

[David M]

Originally Posted by Beausoleil

The reels would be used while trolling under power - the boat is a sportfisherman, not a sailboat. So the 24V bank would be continuously charging.

I was leaning towards recommending he go with the equalizer setup, since the loads are non-critical motors (he might disagree when if he ever charters!). My thinking was that a DC/DC converter was more for truly voltage-critical loads like sensitive electronics like an SSB, not electric motors.

And I'd want to make sure that anything I recommend won't come back to bite him later, like the possibility of a non-isolated system causing problems like electrolysis or a floating ground/negative on the 12V side.

Yes, I realize it's a power boat. I also understand that when his engines are turning his alternators are producing 24 VDC.

Avoiding tapping off a single 12 volt battery is not so much for the benefit of the electric reel. The real benefit is to avoid dropping the voltage to the 24 volt loads.

How much current does the electric reel draw?

My question still is, does the boat have a genset that is normally in operation producing 120 VAC or 240 VAC or both while he is underway? This makes a difference in how he could keep dedicated 12 volt battery(s) charged.

A correctly engineered electrical load will be able to tolerate some voltage changes to a 12 VDC system that are not extreme...extremes like going above 14.5 volts or below 11 volts as an example.

I think the bottom line here in this situation is that the electric reel is going to be such an intermittent load that I would not worry about tapping off one of the 12 volt batteries in the 24 volt bank, especially if it is a larger battery like an 8-D. If it were a constant load off of one of the 12V batteries then I would be concerned.

If you want to completely avoid possible dirty DC caused by an electric reel then you will need a dedicated 12V battery which is powered by a dedicated charger whose only load is the battery and the reel. As I said though, well designed DC electronics can handle some degree of dirty DC power.

In general, you want your DC system to be what is called a floating system which avoids stray DC currents running through the boats metal causing potential electrolysis problems. I realize this is impossible with the engines but something is better than nothing.

I have to get to work. Talk to you this evening Jon.

[Beausoleil]

Originally Posted by David M

...My question still is, does the boat have a genset that is normally in operation producing 120 VAC or 240 VAC or both while he is underway? This makes a difference in how he could keep dedicated 12 volt battery(s) charged.

...

I think the bottom line here in this situation is that the electric reel is going to be such an intermittent load that I would not worry about tapping off one of the 12 volt batteries, especially if it is a larger battery like an 8-D. If it were a constant load off of one of the 12V batteries then I would be concerned.

If you want to avoid possible dirty DC caused by an electric reel then you will need a dedicated 12V battery whose only load is the reel.

He's got a genset for use at anchor - the house AC normally comes off a 24V/4800VA inverter/charger

Simplicity is why I was considering recommending the dedicated DC-DC converter option. My thoughts were that the increased cost of the converter might be more than offset by the savings of the increased labor costs required to install a dedicated 12V battery and charging system, or less so the extra wiring required for a battery equalizer (three wires, +24V/+12V/return) from the battery bank versus just two wires from a breaker in the 24Vdc panel. IOW, the total installed cost of a DC-DC converter system may be less than a dedicated 12V system, or a battery equalizer system. Am I over-thinking this?

From strictly a safety point of view, the dedicated 12V system would be preferred, but probably the most expensive to install. The battery equalizer system would probably be the most robust (fewer points of failure). The DC-DC converter is requires fancier electronics, but the wiring is simpler, and one with an isolated ground would probably be safer (assuming the electric reels have a three-wire system with an isolated ground - I'll have to ask him for the reel specifications...)

[Beausoleil]

Originally Posted by David M

Yes, I realize it's a power boat. I also understand that when his engines are turning his alternators are producing 24 VDC.

Avoiding tapping off a single 12 volt battery is not so much for the benefit of the electric reel. The real benefit is to avoid dropping the voltage to the 24 volt loads.

How much current does the electric reel draw?

Talked to the reel manufacturer - 7A no load, 12-15A under typical loads, has an electronic cut-off when it senses 55A.

Originally Posted by David M

My question still is, does the boat have a genset that is normally in operation producing 120 VAC or 240 VAC or both while he is underway? This makes a difference in how he could keep dedicated 12 volt battery(s) charged.

Yes - two gensets, about 12kVA each

Originally Posted by David M

A correctly engineered electrical load will be able to tolerate some voltage changes to a 12 VDC system that are not extreme...extremes like going above 14.5 volts or below 11 volts as an example.

The reel manufacturer's tech person I talked to gave me an example where a customer tried to run two reels off a single Newmar 24/12-50A converter and could only get good performance with one reel at a time. Makes perfect sense to me.

I also talked to my neighbor, and he'd like to not have to run a genset while trolling - and I agree: running a 12kVA genset to drive a 30A 12V charger is horrendously inefficient. His fuel bills are bad enough...

Originally Posted by David M

I think the bottom line here in this situation is that the electric reel is going to be such an intermittent load that I would not worry about tapping off one of the 12 volt batteries in the 24 volt bank, especially if it is a larger battery like an 8-D. If it were a constant load off of one of the 12V batteries then I would be concerned.

If you want to completely avoid possible dirty DC caused by an electric reel then you will need a dedicated 12V battery which is powered by a dedicated charger whose only load is the battery and the reel. As I said though, well designed DC electronics can handle some degree of dirty DC power.

In general, you want your DC system to be what is called a floating system which avoids stray DC currents running through the boats metal causing potential electrolysis problems. I realize this is impossible with the engines but something is better than nothing.

I have to get to work. Talk to you this evening Jon.

When I talked to the tech with the reel manufacturer, he said people tend to use these things heavily, so use isn't really "intermittent". I don't do much deep-sea fishing, so I won't argue that one... I guess the reels would work a lot more than his windlass does!

I definitely like the idea of having isolation on the ground side, but I couldn't find a isolated marine converter which could handle even 30 amps for more than a few milliseconds.. A tech rep with one of the equalizer vendors (Vanner) said that's one nice thing about an equalizer - since they can draw from the batteries "directly" they can handle peak loads better...

I did a quick design using two Victron 24/12-60A DC-DC converters, each running off an available 30A breaker on the 24V distribution panel in the engine room (there's a dedicated 24V panel up at the bridge, with a 24/12 DC converter there for the electronics). Using 6AWG cable, it looks like I get about .6V drop in a 25ft run to the port (and starboard) converter location - looks good, since with a nominal 27V on the 24V bus with the engine alternators running, we have plenty of leeway. Then a short run (5 ft) of 8AWG cable for the 12V from the converter to a water-resistant Hubbell 24Vdc connector under the gunwale. The reel's power pigtail would connect to it. Total retail cost of the hardware and cable would be about $1400.

My concern about the Victron (Orion line) is that it's not IP-65 rated - says install in a cool, dry location. Yeah, right - in a boat's engine room? Mastervolt doesn't have one large enough - I guess he could go with a Newmar 50A one (current limited to 50A...) and install a 40A breaker on the 12V side, and hope it doesn't trip under heavy load very often...

If he went the DC equalizer route, the cable runs would be shorter (he could run off the engine batteries), but the 12V side would be longer (equalizer needs to be pretty much co-located with the batteries), necessitating bigger cables - more money. Probably a wash with the converter configuration.

I'd guess the dedicated 12V battery route would be roughly the same up-front cost: either bigger cables from a centrally located 12V battery and a 30-50A charger, or dedicated smaller port/starboard batteries, chargers, and cables...

Too many ways to skin a cat - I'm just trying to help him design an idiot-proof system which is still robust...