diy solar

diy solar

DC-DC charger (B2B) options and general discussion

pajarojo said:
Right you are. Looks like I would need to plan on 1200W+12 to24v DC converter.
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If you find something keep me posted, I've been looking for some time. Most likely end up with Victron, could always parallel them to get 30a 24v. Even with a 165a alternator, it might be marginal with 2 in parallel with accessories on like AC and high blower fan speed.
 
pajarojo said:
To add to the confusion and intrigue, Kisae has removed the DMT-2430 from their website but if you google it, there's now a spec. sheet floating around for a DMT-2450 charger. If this is a forthcoming product it would be great for my needs if I could input ~14ish V 100A from my van's customer connection point and have it charge an 8s 280Ah EVE battery at 24v/50A and quit when the current drops to 10A.
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Last I spoke with Kisea @ the end of June 2020:

'Thank you for writing to KISAE.

At this time, the only 24V DC-DC charger model that we have available is the DMT2430 (datasheet attached).

No, the DMT2430 has always been our only 24V DC-DC charger product.

Hopefully this can be suitable for your application. Please let us know if you do have any questions.

Best regards,
Lawrence
KISAE Technology'

From the manuals it only does one or the other as far as charging:

'With two inputs available, the house battery will be charged from either the engine while underway, or via the solar panels when stationary. The process to choose either engine or solar is fully automatic and both functions are controlled from within the unit itself without the need for external relays.'
 
Renogy makes 20A, 40A, and 60A versions of their DC-DC charger. I'm using the 40A version to charge a 400Ah LiFePO4 battery. The Victron Orion is only 30A. I have a 220 amp alternator on my RV, and I was tempted to get the Renogy 60A version to charge the battery faster, but the terminals are the same for all three versions, and the 60A version's terminals start to get warm when used at max capacity. You need at least 4AWG cables for 60A. No Bluetooth, but it does have an ignition interlock which prevents it from turning on until the engine has been started. I would have like to see an voltage autosense feature, but maybe in the future.
If you want any more than 40A charging from your vehicle alternator, you really need to go to a separate 24V alternator and install a 24V battery pack/BMS. Then get a 24V-12V converter to power your RV's 12Volt bus. This in turn means you can use thinner cables making it easier (and cheaper) to install.
 
Is there a dc-dc charger that can work as an inverter as well? Like 1500W inverter etc. I am only looking for dc-dc and inverter as single unit. Thanks everyone!
 
Pashich said:
Hey guys!
Has anybody bused this charger from AE?
Im waiting for my cells and later on want from time to time charge lifepo4 from truck alternater/starter battery
a.aliexpress.com

87.3US $ 10% OFF|Telun 4s 4 String 14.6v 15v 1a-30a Adjustable Car Charger Lithium Iron Phosphate Battery Solar Constant Current Voltage - Solar Battery Chargers & Charging Kits - AliExpress

Smarter Shopping, Better Living! Aliexpress.com
a.aliexpress.com a.aliexpress.com
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Requires a manual shut off/on. Do you really want that? The higher end chargers will sense when the engine is on. The output voltage is too high. They say it's for Lithium, but it's OK for Lithium when you're actively managing it.
 
HRTKD said:
Requires a manual shut off/on. Do you really want that? The higher end chargers will sense when the engine is on. The output voltage is too high. They say it's for Lithium, but it's OK for Lithium when you're actively managing it.
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No problem with manual switch since I dont want to have my LIFEPo4 always connected to starter battery. Generally I have an old Toyota 199x truck used for camping. Portable solar pannels and mppt. And dc compressor freezer. This system has been working for me for several years. Now want to use lfp instead of starter battery. As far as I understand this charger from AE is cc/cv charger suitable for lfp .
 
Pashich said:
No problem with manual switch since I dont want to have my LIFEPo4 always connected to starter battery. Generally I have an old Toyota 199x truck used for camping. Portable solar pannels and mppt. And dc compressor freezer. This system has been working for me for several years. Now want to use lfp instead of starter battery. As far as I understand this charger from AE is cc/cv charger suitable for lfp .
Click to expand...

Technical parameter:
Product performance: DC to DC (constant current and constant voltage)
Application: 4 series (14.6V) lithium iron phosphate batteries
Input voltage: DC 10V ~ 15V
Maximum input power: 470W
Output voltage: DC 14.6V ~ 15V (± 0.2)
Output current: 1 ~ 30A (adjustable)
Maximum output power: 440W
Conversion efficiency: 93% ~ 97%
No-load current: ≈0.02A
Product size: 210mm × 110mm × 90mm
Applicable environment: -30 ℃ ～ + 60 ℃

With a voltage range like that, the chance of overcharging of the cells seems high to me.
 
HRTKD said:
With a voltage range like that, the chance of overcharging of the cells seems high to me
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Yes, agree. Not so good... Probably can be used only if not charged to soc 100%. But BMS should disconnect then if it finds overvoltage cell than.
One if the tasks for me is not to overload alternator, since the model is from 1990s without any computer on board.
 
Pashich said:
Yes, agree. Not so good... Probably can be used only if not charged to soc 100%. But BMS should disconnect then if it finds overvoltage cell than.
One if the tasks for me is not to overload alternator, since the model is from 1990s without any computer on board.
Click to expand...

The general guideline here on the forum is that you don't want your BMS to be your first line of defense. Instead, your upstream devices should be smart enough, or configurable enough, to manage the charge profile so your BMS doesn't have to step in.
 
HRTKD said:
The general guideline here on the forum is that you don't want your BMS to be your first line of defense. Instead, your upstream devices should be smart enough, or configurable enough, to manage the charge profile so your BMS doesn't have to step in.
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Thank you, makes sense to me too✌️
I'll try to contact manufacturer for this device, maybe voltage could be fixed to no more 14.6. if not than consider another dc-dc charger, maybe more or less budget ones are available.
Upd
checked sticker on their charger - it says 14.6~14.8 +/-0.2%
 
Last edited:
HRTKD said:
Technical parameter:
Product performance: DC to DC (constant current and constant voltage)
Application: 4 series (14.6V) lithium iron phosphate batteries
Input voltage: DC 10V ~ 15V
Maximum input power: 470W
Output voltage: DC 14.6V ~ 15V (± 0.2)
Output current: 1 ~ 30A (adjustable)
Maximum output power: 440W
Conversion efficiency: 93% ~ 97%
No-load current: ≈0.02A
Product size: 210mm × 110mm × 90mm
Applicable environment: -30 ℃ ～ + 60 ℃

With a voltage range like that, the chance of overcharging of the cells seems high to me.
Click to expand...
Wonder if you could put a cheap regulator or step down converter in series before the battery.
 
When it comes to charging an expensive battery bank, don't go cheap. Buy something that doesn't come directly from China. Go back to the beginning of this thread and look at the DC-DC chargers that forum members are using.
 
HRTKD said:
When it comes to charging an expensive battery bank, don't go cheap. Buy something that doesn't come directly from China. Go back to the beginning of this thread and look at the DC-DC chargers that forum members are using.
Click to expand...

The issue there is that I'm trying to follow the charging recommendations of Nordkyndesigns and none of these chargers appear to shut down properly (when current gets down to .033C) and would seem to overcharge the pack (were it not for the BMS). Well, the Kisae DMT series actually does but they max out a 10A for the low current shutoff but that would work for a battery of up to 300Ah and I plan to install 560Ah. As best I can tell, all these 'smart' chargers aren't that smart and the 100% SOC shutoff is probably happening by the BMS, which doesn't seem good to me.

The Victron BMV-712 can control a relay so at this point I'm sort of leaning toward using a 'dumb' power supply and having a BMV shut it down when it gets to the desired SOC that I program it to. (I would still have an overkill BMS on the battery as well)
 
If it's any consolation, there seems to be a fair amount of grumbling about the AC-DC converters also. I use an IOTA Engineering DLS-55 converter to charge my 560Ah of LiFePO4 from shore power. For an expensive device, it's a little goofy.

If I were to implement a DC-DC charger in my system, I would be looking at one from Victron. It fits in with the rest of my Victron equipment (color wise
biggrin.gif
) and I trust Victron. I would never trust a dumb charger in my system.
 
pajarojo said:
The issue there is that I'm trying to follow the charging recommendations of Nordkyndesigns and none of these chargers appear to shut down properly (when current gets down to .033C) and would seem to overcharge the pack (were it not for the BMS). Well, the Kisae DMT series actually does but they max out a 10A for the low current shutoff but that would work for a battery of up to 300Ah and I plan to install 560Ah. As best I can tell, all these 'smart' chargers aren't that smart and the 100% SOC shutoff is probably happening by the BMS, which doesn't seem good to me.

The Victron BMV-712 can control a relay so at this point I'm sort of leaning toward using a 'dumb' power supply and having a BMV shut it down when it gets to the desired SOC that I program it to. (I would still have an overkill BMS on the battery as well)
Click to expand...
Why don't you just buy the alternator controller from Norkyndesigns? http://nordkyndesign.com/product/nordkyn-electronics-vrc-200-charge-reference-controller/
 
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