two chargers

[gettinthere]

I have a Zantrex Freedom 40+ charger.
I was told I could wire a second one in and double the charging capacity. Zantrex confirmed this, but wouldn't supply a wiring diagram.

I'm leary of doing this without specific instructions.

Any sources for this sort of thing?

[Vasco]

Why are you doing this?

[David M]

I have both a 100 amp charger and a smaller backup 30 amp charger. It works okay to run two chargers at once but there is a downside that I will explain.

To answer your question about wiring, you wire the chargers like you would for any charger. Pos to Pos and Neg to Neg. Ideally wire both chargers directly to the battery post or to the closest place to the battery that you can. It is always best to wire directly to the post. This way you have less of a chance of getting a voltage drop from a terminal with too much resistance. The other reason I say directly to is in case you have a terminal or wire failure.

Another and slightly less desirable way that would work is to wire one charger to the other. Pos to Pos and Neg to Neg and then send one pair of charging wires to your batteries...again Pos to Pos and Neg to Neg. Electrically this is the same as my first wiring description. The difference is in the reliability of having each charger tied directly to the battery.

The downside is if you have a three stage charger, running two chargers will probably screw up the three stage charging process which really is the best way to charge your batteries. The chargers would have to communicate with each other to do this, and of course they don't do this.

If you have the money, I would buy a modern larger three stage charger that is more than capable of keeping all your batteries charged. Keep the better of your two existing smaller chargers, wire in both chargers and normally use the larger charger that you just bought. Use the backup charger for exactly that, in case your primary charger fails. Don't normally run both chargers, although it can be done, its just not the ideal thing to do.

[Vasco]

Originally Posted by David M

I


If you have the money, I would buy a larger charger instead and keep things simpler. Keep the better of the the two smaller chargers, wire it in and normally use the better-modern-larger charger that you just bought. Use the backup charger for exactly that, in case your primary charger fails.

My thoughts too. I'd get a 2000w inverter with a 100 amp charger. Their prices have come down and I've seen some for about $750.

[btrayfors]

You can buy an Iota 75A or 90A charger for a LOT less money, and these are hard to beat at any cost.

I'd forget the idea of wiring two chargers together (except for the Iotas which are designed for this, i.e., you can wire any two identical models together).

Don't forget the power requirements. A 75A charger can run OK on a 15A circuit, but the 90A model requires 20A.

Bill

[Pelagic]

With my 24v Battery upgrade I also purchased a new Victron 70/3000/24 Combi Charger/ Invertor so that this new 70amp charger would complement my existing Victron Skylla 50A charger.

Both are smart chargers and are individually wired to my HD Studs

I have been logging a number of tests which I could show you but I can’t figure out how to attach an Excel file on here.

Basically when you have a large Amp hour deficit both chargers (wired as I have them) will put out to individual temperature controlled capacity.

Then as you get closer to absorption phase (SOC 94%) the 50A drops down completely, I shut it off and if I am on shore power the 70 will keep it on Float (SOC 100%)

In a 24 hour period, I consume 10% of my House Bank capacity. So at anchor using my Genset to power chargers my optimum operating profile is to keep the batteries between 84% and 94% which translates into 3 hours of generator use for every 24 hours.

[Charlie]

I have a pair of Iota 55 amp chargers. I only have one in operation right now b/c I am not full time cruising. I emailed Iota and they recommended this mehtod of using two charger on my boat which has 4 6v batteries. Hook one charger up to two of the batteries and the other charger up to the other two batteries. My understanding of the reason for this is because -- The three stage chargers don't synch very well. I can forward you the email if you want and if I can find it.

[gettinthere]

Originally Posted by Vasco

Why are you doing this?

Already have the one charger but I want more charging capacity.
If I add a second 40+ I'll have 80 amps charging from the genset.

I've been told by a couple of sources that if the chargers are identical it is OK.
The 40+ is a 3 stage smart charger with temp sensors and equalization so I don't think it's as simple as wiring the output to the pos/neg.

I'll be upgrading the house battery to over 800 amps plus a start battery.

[CorrinaCorrina]

When placing a second charger onto your battery bank you want to attach the positive of the second battery charger as far away from the positive of the first battery charger. Ideally you would like to have them at opposite ends of the battery bank. Reason for this is that the battery bank will act like a huge capacitor and will allow for a more efficient charge. If you have a shunt in your negative, run the negative of each charger to one side of the shunt and have a significant wire size from the battery bank to the other side of the shunt. Ideally you would want to run 2/0 wire from battery charger to the batteries, both positive and negative. How big of a bank do you have, what type of batteries(wet,AGM,GEL) and at what voltage? The answer to this could change the layout of your charging system.

[gettinthere]

The bank is currently about 400 amps but I'm planning on changing to about 800+ amps.
I'll stick to wet cells. The charger I have does have settings for all three types of batteries. The batteries will all be the same type. The starting battery is wet also.

[Beausoleil]

I'm currently fine tuning our charging system for our 800 A-hr AGM bank: a Magnum Energy MagnaSine 2800 inverter/charger (125A charger), a Balmar 190A dual-output alternator with a Balmar MaxCharge MC-612 regulator, and an Iota DLS-75/IQ4 charger. The chargers are driven by either a Westerbeke 7.6 BTD genset, or 2 x 30A/125V shorepower connections.

I haven't run the engine alternator simultaneously with any of the chargers. But I can say that while bulk charging - with almost identical charging profiles - I've seen the Magnum's battery monitor register as much as 179 Amps going into the battery bank. Without detailed testing, I can't confirm (but I do expect) that if the bank was discharged more deeply, I'd see the full output of both chargers when in bulk mode - 200A.

Since the two chargers aren't synchronized, I shut down one once either goes into the absorption phase. Since absorption is voltage-limited (14.5-14.9V @ 77°F/25°C for our Fullriver 6V AGM bank) and typically the currents are less than 75A, I usually just shut off the Magnum charger. And it appears that the Iota charger, with its PWM charging technology, can actually maintain a higher current output into the battery bank for a longer period, reducing the time it takes to get the SOC to 100%.

Of course, all that's moot when you're on the hook and don't want to run the genset for hours to ensure a full charge. And we do have a wind generator (SWWP Air Breeze Marine), but it typically goes into regulation early in the absorption phase.

One problem I have seen (and I'm starting to work with Magnum Energy's tech support on this), is that when on shorepower, unless the charging voltages of the MagnaSine and the Iota DLs are matched, the MagnaSine will actually switch to invert mode (stopping charging), even though the AC input is still well within spec for a 125V/30A service. What's got me scratching my head is that the MagnaSine is running off one 125V/30A shorepower service, and the Iota is running off the other I've got it tweaked to where it doesn't happen anymore, the the problem seems to a bit more pronounced when running off the genset (which also has two 30A service legs).

I know this has wandered off topic a bit, but my main point is that when a bank is depleted enough, charging from two unsychronized charging sources is one way to quickly get the bank through the bulk charging phase.

[CarlF]

I also have two chargers set up and have slowly come to understand how they interact (I think). Please note - I am no expert at this. This is just trial and error observation.

Both chargers will charge fine during the bulk phase (when the battery bank voltage is below the charger's absorption voltage setting). The problem comes when one charger goes into float because the other charger has a slightly higher absorption voltage and the battery bank has now risen to the higher voltage. This leaves you with one charger at a low float voltage providing almost no amperage. If you tweak the absorption voltage set point you can impact which charger drops out.

I believe that some chargers (but not mine) can be set to have a minimum amount of absorption time (like two hours). If you set this charger to have a slightly lower absorption voltage, then both chargers will stay at an absorption voltage charging normally at a slowly declining amperage. I don't believe that this would hurt the batteries since the amperage will decline as normal and staying at an absorption voltage for a few extra hours does no damage to the bank.

Or one could also simply decide that you like to have one charger drop out when the bank get's to absorption voltage.

A real advantage to two chargers is redundancy. You can have a charger fail without serious inconvenience. I've seen that the cost of two lower amperage chargers is not much more than one high amperage charger.

Any real experts out there who actually understand this stuff?

Carl

[gettinthere]

Carl
Are your two chargers identical?

[CarlF]

Not identical chargers - different amperage and different models - but both are 3 stage smart chargers with temperature compensation.

I really don't think the chargers need to be identical as long as the charge voltage and amperage doesn't go too high for the battery type - which a smart charger will look after assuming it's set up right.

I think chargers are different than alternators. If you have two alternators, I think you're supposed to have the same type and size - but I don't really know. Maybe it's just if you are running two alternators off one regulator.

Beausoleil doesn't mention his battery type or bank size. If it's a traditional flooded lead acid, I've always been told that you don't want the charge amperage to exceed 15% of the bank amperage. Many AGM's batteries can take a substantially faster charge.

Nigel Calder wrote a piece on new battery chemistry in last February's Professional Boatbuilder magazine (which is available on line). While I found this really interesting, I also think I might keep the topic in reserve at this year's holiday parties. Sometimes I like to clear out a little space around me at these parties. Talking about "Battery chemistry" should do the trick.

Carl

[Beausoleil]

Originally Posted by CarlF

Beausoleil doesn't mention his battery type or bank size. If it's a traditional flooded lead acid, I've always been told that you don't want the charge amperage to exceed 15% of the bank amperage. Many AGM's batteries can take a substantially faster charge.

Originally Posted by Beausoleil;

I'm currently fine tuning our charging system for our 800 A-hr AGM bank:

They're a bank of four Fullriver DC400-6 AGMs. Conservatively, at a 40% charge rate, I should be able to bulk charge at 320A. I should also mention that while the Magnum is temperature-compensated, the Iota isn't. Iota basically claims that with PWM charging, they can dispense with monitoring battery temperature because by pulse charging, the batteries temperature doesn't rise enough to begin gassing.