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Old 16-11-2019, 01:42   #1
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Series and Parallel impossible? 6 batteries, 72 Vdc, One charger

I am simply not finding step up DC to DC transformers to run a 72 VDC 3000 watt device and am now heading down path....

6-12VDC batteries in series.

Which is fine until I come to how to charge. Is there a way to charge all 6 from the same source at the same time while the 72V device still operates?

I have seen solutions where switches change the batteries from series to parallel however this is a manual switch and the motor must stop during charging.

Ideally I want one large solar charger that charges all six batteries at the same time while the 72VDC device is operating. Are my only two possible routes

1. All batteries in parallel and massive stepup convertor which I have yet to find? Or

2. Batteries in series and 6 separate battery chargers connected to 6 isolated solar banks?
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Old 16-11-2019, 02:12   #2
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Re: Series and Parallel impossible? 6 batteries, 72 Vdc, One charger

1, Six batteries of 12 Volt connected parallel, is still 12 Volt; one charger providing 12 Volt, can charge all of them at the same time
2. Six batteries of 12 Volt in series, indeed gives you 72 volt nominal. Again, one charger set at 72 Volt can charge all of them at the same time.

The latter would give you what you want: charging and using the device at the same time.

If you have only a 12 Volt charger, then you need seven batteries. The 12 Volt charger connected to the single 12 Volt battery, and then a DC to DC charger from 12 to 72 volt, to charge the six other batterers in series. Hmmm, or is it that finding that kind of DC-DC charger difficult? Maybe check with Rich in Taiwan, talk/email with Martina (sales manager), she might be able to help you: https://www.rich-electric.com/index....wer-inverters/
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Old 16-11-2019, 03:54   #3
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Re: Series and Parallel impossible? 6 batteries, 72 Vdc, One charger

Quote:
Originally Posted by HankOnthewater View Post
1, Six batteries of 12 Volt connected parallel, is still 12 Volt; one charger providing 12 Volt, can charge all of them at the same time
2. Six batteries of 12 Volt in series, indeed gives you 72 volt nominal. Again, one charger set at 72 Volt can charge all of them at the same time.

The latter would give you what you want: charging and using the device at the same time.

If you have only a 12 Volt charger, then you need seven batteries. The 12 Volt charger connected to the single 12 Volt battery, and then a DC to DC charger from 12 to 72 volt, to charge the six other batterers in series. Hmmm, or is it that finding that kind of DC-DC charger difficult? Maybe check with Rich in Taiwan, talk/email with Martina (sales manager), she might be able to help you: https://www.rich-electric.com/index....wer-inverters/

Thanks for the idea. It never occurred to me that a 72 Volt solar charger exists. I found they do.

So I can just use one large charge controller.

Of course it is such an unusual animal that 6, 12-Volt charters is 1/5th the price.

The big down side with the six separate controllers is finding the room to mount them and protect them from the weather.
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Old 16-11-2019, 09:47   #4
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Re: Series and Parallel impossible? 6 batteries, 72 Vdc, One charger

Boosting voltage is very inefficient.

The usual practice is to rectify AC mains-style input, whether genset or shore power, to a high "backbone" buss voltage, from 250-370Vdc range

270Vdc is very common now in industrial, medical/scientific, aviation & military applications, so excellent equipment can be found in the aftermarket very cheaply.

And then step down (buck conversion) to multiple lower "normal" voltages either with discrete/modular converters at PoL (point of load), or to intermediate buss voltages, say 96V or 48V in some applications

Called distributed power architecture (DPA)

3000W is a fair bit of juice, often accomplished with an array of converters, the main "driver" unit with the control circuitry, paralleled with dumb booster modules to increase the amps output.

Vicor is a leading vendor in OTS versions of such system components, Lambda (now TDK) as well.

Elcon is a quality vendor of high-voltage chargers running directly off mains. Also Brusa and Manzanita, high amps and very high quality obviously not cheap.

At lower amps, from the eBiking world, check out the Grin Tech "Satiator" charger, only 300W but can be stacked in parallel.

Note LFP would be a more suitable bank chemistry for less voltage sag at higher C-rates, quicker re-charging.

Also that trying to go cheap for this kind of setup risks wasting a lot of money on gear turns out later to not be suitable.

Anything over 60V gets lethal, best to at least consult with experienced professionals, have them sign off on the design and component selection, and inspect the final implementation.

Will you be trying to get insurance?

I assume this is a propulsion application?

If so you will need a huge array of solar panels, a generator would be more practical.

How many Ah per day at nominal 72V do you expect to consume?
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Old 17-11-2019, 12:36   #5
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Re: Series and Parallel impossible? 6 batteries, 72 Vdc, One charger

Never tried this, but...

1. Connect 24V PV via 24V charge controller to 24V seriesed 12V.
2. Connect 24V PV via 24V charge controller to 24V seriesed 12V.
3. Connect 24V PV via 24V charge controller to 24V seriesed 12V.
4. Connect the three in series to get 72 V.

To enforce there being relatively equal charge levels on each 24V set, a fourth PV panel would need to be switched to the weak sister via 3 pairs of solid state relays. The V sensing could a programmable relay with 3 analog inputs. Three programmable relay outputs would drive the six SSR inputs. The sensing + switching hardware would run ~ U$500.
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Old 17-11-2019, 12:57   #6
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Re: Series and Parallel impossible? 6 batteries, 72 Vdc, One charger

What is the 3KW 72 volt device? Inquiring minds want to know.
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Old 17-11-2019, 13:54   #7
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Re: Series and Parallel impossible? 6 batteries, 72 Vdc, One charger

Quote:
Originally Posted by pbmaise View Post
I am simply not finding step up DC to DC transformers to run a 72 VDC 3000 watt device and am now heading down path....

6-12VDC batteries in series.

Which is fine until I come to how to charge. Is there a way to charge all 6 from the same source at the same time while the 72V device still operates?

I have seen solutions where switches change the batteries from series to parallel however this is a manual switch and the motor must stop during charging.

Ideally I want one large solar charger that charges all six batteries at the same time while the 72VDC device is operating. Are my only two possible routes

1. All batteries in parallel and massive stepup convertor which I have yet to find? Or

2. Batteries in series and 6 separate battery chargers connected to 6 isolated solar banks?
Out of curiosity what is the " device".
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Old 17-11-2019, 14:10   #8
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Re: Series and Parallel impossible? 6 batteries, 72 Vdc, One charger

Really is not needed if it's a secret.

But we do need to know how many amps it pulls for what sort of burst times if high

as well as total Ah per 24hrs,

in order to help with decent advice.
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Old 17-11-2019, 14:24   #9
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Re: Series and Parallel impossible? 6 batteries, 72 Vdc, One charger

Try here. I don’t know if they can help

https://power.murata.com/products/dc-dc-converters.html
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Old 18-11-2019, 01:01   #10
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Re: Series and Parallel impossible? 6 batteries, 72 Vdc, One charger

Quote:
Originally Posted by john61ct View Post
Really is not needed if it's a secret.

But we do need to know how many amps it pulls for what sort of burst times if high

as well as total Ah per 24hrs,

in order to help with decent advice.
I received more specifications from the manufacturer today as well as their recommendation I go up to the 4kw motor. Yes this is propulsion application.

The good news is the detailed specifications indicate I can buy this brushless DC motor in 48 V or 60 V versions as well. That means instead of 6 primary batteries to provide the high amp current for short bursts of speed I only need 4 or 5.

My thinking is to go with 4 or 5 sealed 40ah or 45aH 12volt lead acid batteries featuring 50A or 65A high current demand while at full load (3kw motor) . These will be hopefully exhausted to no lower than 50% remaining charge before the high demand for power has been satisfied.

I will use a second set of splash proof portable lithium battery packs to charge each primary battery using one charge controller per primary battery.

The lead acids will remained fixed within a rain proof vented box in the vehicle and the portable lithium batteries will be charged either on land or aboard.

I anticipate I will need two sets of lithium batteries so one set can always be charging while the other set is recharging the lead acid batteries. This prevents downtime waiting for charging.
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Old 18-11-2019, 01:43   #11
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Re: Series and Parallel impossible? 6 batteries, 72 Vdc, One charger

Quote:
Originally Posted by pbmaise View Post
I received more specifications from the manufacturer today as well as their recommendation I go up to the 4kw motor. Yes this is propulsion application.

The good news is the detailed specifications indicate I can buy this brushless DC motor in 48 V or 60 V versions as well. That means instead of 6 primary batteries to provide the high amp current for short bursts of speed I only need 4 or 5.

My thinking is to go with 4 or 5 sealed 40ah or 45aH 12volt lead acid batteries featuring 50A or 65A high current demand while at full load (3kw motor) . These will be hopefully exhausted to no lower than 50% remaining charge before the high demand for power has been satisfied.

I will use a second set of splash proof portable lithium battery packs to charge each primary battery using one charge controller per primary battery.

The lead acids will remained fixed within a rain proof vented box in the vehicle and the portable lithium batteries will be charged either on land or aboard.

I anticipate I will need two sets of lithium batteries so one set can always be charging while the other set is recharging the lead acid batteries. This prevents downtime waiting for charging.
I hope that you realize that the size batteries you are talking about means extremely short range. 3KW at 48 volts translates to 62 amp draw. 4KW is an 83 amp draw. As you said lead acid batteries should not be discharged more than 50 percent meaning that you have full power for a maximum of 30 minutes. Why would you use lead acid batteries as intermediate power if you have lithium batteries. Lead batteries charge much more slowly than lithium. How are you going to charge the lithium batteries? Is this is going to push a 65 foot catamaran. 4KW is a little over 5 horsepower. Even if you are planning two 4KW motors your best horsepower is only about 10.7 HP. Even a light headwind will stop all forward progress of that size boat with only 10 horsepower. You really need a propulsion engineer before proceeding.
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Old 18-11-2019, 02:00   #12
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Re: Series and Parallel impossible? 6 batteries, 72 Vdc, One charger

A schematic diagram showing the all components is going to be helpful here. Are the PV panels still on the table?
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Old 18-11-2019, 02:14   #13
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Re: Series and Parallel impossible? 6 batteries, 72 Vdc, One charger

First off, primary battery means used once and discarded, cannot be recharged with electricity and reused.

Lead batteries as you describe just do not exist.

It is foolish to charge one set of batteries from another.

Your application will require ICE power generation in any case, might as well be running that to support your electric motor(s) directly

Of you're thinking recharging from solar, the wait will be days or weeks, not hours.

These "short bursts of speed" are for what? avoiding a Kraken that will then sink back into the depths, never to be seen again, so you can resume rowing?

Sorry but that's just how fantastical all this is.

Back to the drawing board.

https://upload.wikimedia.org/wikiped...e_Montfort.jpg
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Old 18-11-2019, 04:11   #14
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Re: Series and Parallel impossible? 6 batteries, 72 Vdc, One charger

Think dinghy size vehicle this application is not for my trimaran.

Solar is still in the mix only to recharge the portable batteries and solar regulators are a really cheap way to control charging of the lead acid batteries.

While my vessel can be outfitted with as much as 7kw of solar panels, my plan is to put solar on land.

I looked into all lithium approach.

I found some higher performance portable lithium packs. For example Ryobi packs a big punch at 40 volts or 19 volts. Their larger packs hold up to 240 watts each. The problem is price. Even the knock off brand Powilling comes in at 48.5 cents per watt.

Accepting the compromise of low amperage high storage volume lithium batteries along with lead acid equates to less 1/2 the price per available watt.

I use the term "available watt" since about 50% of lead acid capacity will not be tapped.

I apologize for inventing terms as I go like "primary battery" and agree there are undoubtedly other applications of the same term applied differently.
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Old 18-11-2019, 09:37   #15
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Re: Series and Parallel impossible? 6 batteries, 72 Vdc, One charger

LI chemistries other than LFP are much more likely to explode into flames at the least convenient time.

The smaller the boat the less appropriate lead's extra weight and space taken.

If cost is such a big factor make sure to get the design right or much of the money will be wasted.

What is the motivation for using electric rather than a basic outboard?

In addition to the required data above, add

How many kW of panels?
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