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48v DC Generator to 48v Battery Bank

At 2400 cycles, those are actually better than most in that application. Given how you plan to use them, it sounds like a good choice.
 
Going to update this thread since the generator arrived today. It was a T-Mobile surplus and there quite frankly wasn't a whole lot of information on it, but it all turned out well so far. So maybe this will help someone else some day.

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It was a brand new/old unit from 2015. It was a unit that was packaged for holding, no oil or fluids stored in it of any kind. It even came with an unopened manual, pad mounting templates, and the schematics necessary to get my permits.

Once I cracked the crate open, I did what any normal person would do when opening a brand new item. I took it apart. Ok so not quite apart but I wanted to see more than just the casing. I'll post the pictures at the very end but some interesting bits to this thing.

1. Surge protected load panel
2. On board DC/DC converter
3. Extended run oil tank. 500 run hours before maintenance
4. Start/Exercise only needed every 6 months via the engine. It uses the onboard batteries to exercise every 30 days without motor start.
5. Onboard storage for (4)12V/100Ah batteries. These are considered it's "starting battery" for 48V/100Ah. This was a really neat feature as I happen to use 12V/100Ah batteries now and I'll be able to slide them right in instead of discarding them.
6. "Auto" mode that is voltage based. Kicks on when voltage drops below 48V. Kicks off when voltage exceeds 52.5V. No it won't fully top of my batteries, but this ensures that when the grid kicks back on, the SI's won't end up charging the generator. This is also a plus as I was originally planning on using my SIs as a controller. This might also allow me to keep the batteries at a steady state and essentially power the SI's via this generator alone.

The last thing I was happy about is the consumption. It isn't fixed load as I originally thought. So with what my batteries would draw to charge I'm looking at roughly half a gallon of propane per hour. On a standard bbq tank (4 gallons) I'd be able to run for 8 straight hours of battery charging.

My conclusion so far is that this thing seems to be made as a perfect compliment to either a offgrid/hybrid 48V system. I'll post more once I get my permits, pour some concrete, do some trenching, lay some pipes, and run some electrical. Easy peasy.

For the visually excited:

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With nine phase alternator it doesn't need much if any DC supply filtering.

Question that you should find out is how it is doing regulation. There are several possible ways depending if it is permanent magnet rotor or slip ring field winding current regulation. It can be a combination of motor speed and electronic regulator.

From a fuel consumption point of view you don't want a fixed engine speed. It will usually get less fuel efficiency if loaded less then 40-50% of engine hp rating.

If I was to take a guess, I would say it probably works like an inverter generator in ECO mode. They have permanant magnet alternator that produces DC voltage from rectified multiphase AC alternator output. The DC voltage depends on engine speed and electrical load. The regulator likely keeps engine speed high enough with some amount of overhead DC voltage margin that fine voltage regulation to output is done with switching power supply regulator.

The generator DC output is smooth enough to run your inverter directly without any batteries connected, as long as you don't go over 150A's.

Question is whether it is just a fixed limiter current (150A). You have to be sure when your battery is low the generator does not put excessive charging current to your batteries. Make sure you monitor charge current. If it is fixed at 150A (until voltage regulation) you are pretty much screwed for small capacity battery. Check around the electronic regulator to see if it has a current limit adjustment.

The application of this generator was for grid backup of cell site so may not have been intended to charge batteries. In the worse case the generator shuts down if load exceeds 150A and it cannot maintain the regulated voltage output.

It you destroy your batteries the generator won't be such a good deal.
 
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With nine phase alternator it doesn't need much if any DC supply filtering.

Question that you should find out is how it is doing regulation. There are several possible ways depending if it is permanent magnet rotor or slip ring field winding current regulation. It can be a combination of motor speed and electronic regulator.

From a fuel consumption point of view you don't want a fixed engine speed. It will usually get less fuel efficiency if loaded less then 40-50% of engine hp rating.

If I was to take a guess, I would say it probably works like an inverter generator in ECO mode. They have permanant magnet alternator that produces DC voltage from rectified multiphase AC alternator output. The DC voltage depends on engine speed and electrical load. The regulator likely keeps engine speed high enough with some amount of overhead DC voltage margin that fine voltage regulation to output is done with switching power supply regulator.

The generator DC output is smooth enough to run your inverter directly without any batteries connected, as long as you don't go over 150A's.

Question is whether it is just a fixed limiter current (150A). You have to be sure when your battery is low the generator does not put excessive charging current to your batteries. Make sure you monitor charge current. If it is fixed at 150A (until voltage regulation) you are pretty much screwed for small capacity battery. Check around the electronic regulator to see if it has a current limit adjustment.

The application of this generator was for grid backup of cell site so may not have been intended to charge batteries. In the worse case the generator shuts down if load exceeds 150A and it cannot maintain the regulated voltage output.

It you destroy your batteries the generator won't be such a good deal.

So when I saw the Alltrax DC Motor Controller onboard, I assumed it would control it. Is that not the case?

I'm thinking there has to be something that limits, because it has a 48V/100Ah capability onboard. So it needs to have the ability to limit that charging with either the controller board or another battery charge controller - which I haven't found yet.

Edit:
Ok found the wiring diagram.
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The controller has web access with settings according to the manual. It looks like engine speed, and converter current output is read only, so it is not user configurable. But it was the description of the "Auto" mode that gave me some confidence that it should work.

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The way I read that, it sounds like that's how my SI system would be set up as well, and "Genset output is actively limited to prevent battery recharge current" gives me the impression that something acts as an active limiter. The problem is, I don't know what or if it's configurable yet - still pouring over the manual. Not sure how it knows my battery charge rates or size. Any ideas?
 
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Does it have provision for a remote current sensor?
Without one, it couldn't know if it was charging battery at 100A, or if load was pulling 90A and battery was charging at 10A.
Sunny Island knows when power comes from AC, because it decides how much to push or pull from DC.
When a DC charge controller is used, Sunny Island knows either from battery shunt or data link if the charge controller supports one. But, Sunny Island doesn't tell DC charge controller to adjust current during bulk charging; it only switches bulk/absorption/float mode and voltage limits.
So as I add DC charging I'll limit available current by the amount of PV attached to charge controller. Sunny Island can see that and provide additional charging from grid or AC coupled GT inverters.

Propane, and 4 gallon tank for 8 hours. More money than I'd like to spend if ongoing on a monthly basis, OK for power failures. Natural gas cost is preferable. Does it run on both?

Now if you can just capture waste heat, use for water and domestic heating in the winter ...
 
Does it have provision for a remote current sensor?
Without one, it couldn't know if it was charging battery at 100A, or if load was pulling 90A and battery was charging at 10A.
Sunny Island knows when power comes from AC, because it decides how much to push or pull from DC.
When a DC charge controller is used, Sunny Island knows either from battery shunt or data link if the charge controller supports one. But, Sunny Island doesn't tell DC charge controller to adjust current during bulk charging; it only switches bulk/absorption/float mode and voltage limits.
So as I add DC charging I'll limit available current by the amount of PV attached to charge controller. Sunny Island can see that and provide additional charging from grid or AC coupled GT inverters.

I don’t see anything about a remote current sensor, only a voltage sensor.

But, Sunny Island doesn't tell DC charge controller to adjust current during bulk charging; it only switches bulk/absorption/float mode and voltage limits.

So is it possible the generator doesn't care about the current and only switches it based on the voltage?

One more question. Is it possible that my understanding of how batteries charge is incorrect? I've been reading more about charge controllers and it seems a lot of them are sized according to the panels. Anything that references regulation points back to voltage regulation and not current regulation. With one exception - the Sunny Island, which has a charge rate (A)

So that's throwing me for a loop a little. Does amperage only matter when applying to loads and not for a battery? I mean, I know a battery can hold 100Ah, but it doesn't draw at 100A. So if there's no load demand from the battery itself, is there even amperage? Or is it a mathematical formula in which the current is determined by the voltage?

Propane, and 4 gallon tank for 8 hours. More money than I'd like to spend if ongoing on a monthly basis, OK for power failures. Natural gas cost is preferable. Does it run on both?

Now if you can just capture waste heat, use for water and domestic heating in the winter ...

I don’t have natural gas by me, but it does run on the stuff. There’s enough space the theoretically put a heat exchange coil in there, but the cost of the copper and water pump might be more expensive than just going with a heat pump water heater.
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Batteries definitely care about charge current, and it is up to you to stay within what they can handle. Excess current can harm them, and overheating does too. Charge controllers usually have a temperature sensor, because charge voltage needs to vary with temperature. Even in cars - the old regulators for generators adjusted according to ambient temperature.

You should find some way, perhaps a maximum RPM, to keep the generator from charging your batteries at higher current than their data sheet allows.
My SunXtender data sheet says initial inrush current has no particular limit, could even be 5C, if other limits are observed. Some people here question whether that is valid, suggest the battery could be harmed by high current.
The voltage setpoints of the generator may also limit current enough.
 
Batteries definitely care about charge current, and it is up to you to stay within what they can handle. Excess current can harm them, and overheating does too. Charge controllers usually have a temperature sensor, because charge voltage needs to vary with temperature. Even in cars - the old regulators for generators adjusted according to ambient temperature.

You should find some way, perhaps a maximum RPM, to keep the generator from charging your batteries at higher current than their data sheet allows.
My SunXtender data sheet says initial inrush current has no particular limit, could even be 5C, if other limits are observed. Some people here question whether that is valid, suggest the battery could be harmed by high current.
The voltage setpoints of the generator may also limit current enough.

The web access allows a max amperage setting on the controller. The DC/DC converter has that setting as well so I can set that.

What I still don't understand though is how it would carry it out. Because the load panel supplies power to both the loads/batteries as well as the batteries on board. It would need to monitor and regulate both sets of voltages and currents right? The motor controller comes before the load panel, so aside from a couple of breakers how would it do that? I would imagine any setting I change in the controller would affect both battery banks. So how would it be able to tell the difference and regulate the charge current of it's onboard batteries? via the load and battery solenoids? (I can't even pretend to know what those do)
 
My familiarity is with AC generators as DC generators seem pretty rare to start with, but I just found some surplus ones that put out 48v DC. It just happens to match my battery bank perfectly; which is feeding the house via SMA Sunny Islands.

Before I jump on the purchase, I just wanted to confirm as there seems to be conflicting information. My plan is to utilize the Sunny Islands to control the generator - on/off and prevent overcharging. Since they're the same voltage as the battery bank, I don't need any step up or step downs. Do I need anything to control that charge rate?

Is there anything I'd need specifically? Or is it really as simple as - hook it to the battery to replenish the bank?

Thank you,


I bought a Kohler 6SVG couple years back.


I have never even hooked it up yet
 
Your Sunny Island wants to control the generator based on it's calculated SOC measurements - won't your system which appears to be triggered only by voltage, just crank up every time you put 4kw or better load on your SI because it sees a voltage drop? Most of the 48VDC generators I found were 48V power supplies and not regulated battery chargers. I did see a few that were, but they cost more than my Onan 8kw Quiet Diesel inverter generator! I suppose you could shut down the on-board system and control it with one of the relays on the SI and an Atkinson GSCM generator start module, to keep the SI happy.

We tried something similar to this with our system and found that all the juice needs to go thru the shunt attached to the SI, but ultimately found the lack of regulated 4-stage charging to be a deal-breaker. The Sunny Island is a sophisticated battery charger when fed with 120VAC. We did look at an alternative - using solar charge controllers and feeding them with a PM generator end (Onan HDZAA) and a rectifier bridge. The charge controllers could deal with the variable voltage, and most of them are very good 4-stage battery chargers. In the end, we let the SI6048 deal with it but we do still have the parts on hand to affect a quick system if need be in an emergency. Charging the batteries with the SI6048 and a generator gives you more power on hand than the SI can make by itself (plus the SI will crank the generator to deal with high continuous loads), with the 48V generator you're limited to what the SI can make.

Nice looking unit by the way!
 
This little 1-cylinder air-cooled diesel (Hatz) with a PM pancake flywheel generator (Lombardini) made a great DC generator and burn't about a pint of diesel per hour. In the end, our QD8000 runs for a shorter amount of time and made for a better system - both modern PM inverter units are just about the same at turning diesel fuel into electricity, with no clear advantage as to specific fuel consumption. With the QD8000 we have the advantage of running additional loads, and provide 100% of our power needs should the Inverter/Battery system fail.
 

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Sorry, didn't see this thread was old and that you had already taken delivery. Please keep us updated as to your success with this. Curious, how much did it cost if you don't mind me asking?
 
Your Sunny Island wants to control the generator based on it's calculated SOC measurements - won't your system which appears to be triggered only by voltage, just crank up every time you put 4kw or better load on your SI because it sees a voltage drop? Most of the 48VDC generators I found were 48V power supplies and not regulated battery chargers. I did see a few that were, but they cost more than my Onan 8kw Quiet Diesel inverter generator! I suppose you could shut down the on-board system and control it with one of the relays on the SI and an Atkinson GSCM generator start module, to keep the SI happy.

We tried something similar to this with our system and found that all the juice needs to go thru the shunt attached to the SI, but ultimately found the lack of regulated 4-stage charging to be a deal-breaker.

Those are all very good points, and I haven't been able to find any more information as to if there's an on-board charge controller or not but there is an onboard BMS with HVC and LVC. Contact with SMA has confirmed that the SI will do very little with a DC charger and won't control it the same way it does with an AC generator, but as long as I use a shunt then the SI will be able to account for the generator kicking on but it won't be able to control the charging patterns.

On that note, I decided to forgo the VRLA telecom bank. The generator typically powers an AGM bank when used by the telecoms, but reading the manual more and more; I can't help but wonder if LifePo4 is the way to go. Especially with the voltage regulation. Those seem to be much more dependent on voltage and a 16s 3.2v cell bank fits perfectly into those ranges (51.2V Nominal, 48V min voltage as best practice, 54.4V max as best practice). It's something I'm considering now but admittedly it's a lot more complex than just dropping in some VRLAs.

The other problem I had was my setup. An AC generator works really well with a single SMA system. I have one SMA system, one non SMA system, and a sunny island only panel. Getting all of them to stay on without back feeding into the generator was a bit of a challenge. Something I don't have to deal with when it's charging the batteries directly.

Sorry, didn't see this thread was old and that you had already taken delivery. Please keep us updated as to your success with this. Curious, how much did it cost if you don't mind me asking?

The generator was $1500 delivered. There aren't a whole lot of brand new generators available at that price point, lots of used ones in unknown condition though. I felt it was worth the risk at that price point.
 
The generator was $1500 delivered. There aren't a whole lot of brand new generators available at that price point, lots of used ones in unknown condition though. I felt it was worth the risk at that price point.
That is a fantastic price! Good score!
 
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